moduleNameResolver.ts

import {
    append,
    appendIfUnique,
    arrayFrom,
    arrayIsEqualTo,
    changeAnyExtension,
    CharacterCodes,
    combinePaths,
    CommandLineOption,
    comparePaths,
    Comparison,
    CompilerHost,
    CompilerOptions,
    concatenate,
    contains,
    containsPath,
    createCompilerDiagnostic,
    Debug,
    deduplicate,
    Diagnostic,
    DiagnosticMessage,
    DiagnosticReporter,
    Diagnostics,
    directoryProbablyExists,
    directorySeparator,
    emptyArray,
    endsWith,
    ensureTrailingDirectorySeparator,
    every,
    Extension,
    extensionIsTS,
    fileExtensionIs,
    fileExtensionIsOneOf,
    filter,
    firstDefined,
    forEach,
    forEachAncestorDirectory,
    formatMessage,
    getAllowJSCompilerOption,
    getAnyExtensionFromPath,
    getBaseFileName,
    GetCanonicalFileName,
    getCommonSourceDirectory,
    getCompilerOptionValue,
    getDeclarationEmitExtensionForPath,
    getDirectoryPath,
    GetEffectiveTypeRootsHost,
    getEmitModuleKind,
    getEmitModuleResolutionKind,
    getNormalizedAbsolutePath,
    getOwnKeys,
    getPathComponents,
    getPathFromPathComponents,
    getPathsBasePath,
    getPossibleOriginalInputExtensionForExtension,
    getRelativePathFromDirectory,
    getResolveJsonModule,
    getRootLength,
    hasProperty,
    hasTrailingDirectorySeparator,
    hostGetCanonicalFileName,
    inferredTypesContainingFile,
    isArray,
    isDeclarationFileName,
    isExternalModuleNameRelative,
    isRootedDiskPath,
    isString,
    lastOrUndefined,
    length,
    MapLike,
    matchedText,
    MatchingKeys,
    matchPatternOrExact,
    ModuleKind,
    ModuleResolutionHost,
    ModuleResolutionKind,
    moduleResolutionOptionDeclarations,
    moduleResolutionSupportsPackageJsonExportsAndImports,
    noop,
    normalizePath,
    normalizeSlashes,
    PackageId,
    packageIdToString,
    Path,
    pathIsRelative,
    Pattern,
    patternText,
    perfLogger,
    readJson,
    removeExtension,
    removeFileExtension,
    removePrefix,
    ResolutionMode,
    ResolutionNameAndModeGetter,
    ResolvedModuleWithFailedLookupLocations,
    ResolvedProjectReference,
    ResolvedTypeReferenceDirective,
    ResolvedTypeReferenceDirectiveWithFailedLookupLocations,
    some,
    sort,
    SourceFile,
    startsWith,
    stringContains,
    supportedDeclarationExtensions,
    supportedJSExtensionsFlat,
    supportedTSImplementationExtensions,
    toPath,
    tryExtractTSExtension,
    tryGetExtensionFromPath,
    tryParsePatterns,
    Version,
    version,
    versionMajorMinor,
    VersionRange,
} from "./_namespaces/ts";

/** @internal */
export function trace(host: ModuleResolutionHost, message: DiagnosticMessage, ...args: any[]): void;
export function trace(host: ModuleResolutionHost): void {
    host.trace!(formatMessage.apply(undefined, arguments));
}

/** @internal */
export function isTraceEnabled(compilerOptions: CompilerOptions, host: ModuleResolutionHost): boolean {
    return !!compilerOptions.traceResolution && host.trace !== undefined;
}

function withPackageId(packageInfo: PackageJsonInfo | undefined, r: PathAndExtension | undefined): Resolved | undefined {
    let packageId: PackageId | undefined;
    if (r && packageInfo) {
        const packageJsonContent = packageInfo.contents.packageJsonContent as PackageJson;
        if (typeof packageJsonContent.name === "string" && typeof packageJsonContent.version === "string") {
            packageId = {
                name: packageJsonContent.name,
                subModuleName: r.path.slice(packageInfo.packageDirectory.length + directorySeparator.length),
                version: packageJsonContent.version
            };
        }
    }
    return r && { path: r.path, extension: r.ext, packageId, resolvedUsingTsExtension: r.resolvedUsingTsExtension };
}

function noPackageId(r: PathAndExtension | undefined): Resolved | undefined {
    return withPackageId(/*packageInfo*/ undefined, r);
}

function removeIgnoredPackageId(r: Resolved | undefined): PathAndExtension | undefined {
    if (r) {
        Debug.assert(r.packageId === undefined);
        return { path: r.path, ext: r.extension, resolvedUsingTsExtension: r.resolvedUsingTsExtension };
    }
}

/** Result of trying to resolve a module. */
interface Resolved {
    path: string;
    extension: string;
    packageId: PackageId | undefined;
    /**
     * When the resolved is not created from cache, the value is
     *  - string if it is symbolic link to the resolved `path`
     *  - undefined if `path` is not a symbolic link
     * When the resolved is created using value from cache of ResolvedModuleWithFailedLookupLocations, the value is:
     *  - string if it is symbolic link to the resolved `path`
     *  - true if `path` is not a symbolic link - this indicates that the `originalPath` calculation is already done and needs to be skipped
     * Note: This is a file name with preserved original casing, not a normalized `Path`.
     */
    originalPath?: string | true;
    resolvedUsingTsExtension: boolean | undefined;
}

/** Result of trying to resolve a module at a file. Needs to have 'packageId' added later. */
interface PathAndExtension {
    path: string;
    // (Use a different name than `extension` to make sure Resolved isn't assignable to PathAndExtension.)
    ext: string;
    resolvedUsingTsExtension: boolean | undefined;
}

/**
 * Kinds of file that we are currently looking for.
 */
const enum Extensions {
    TypeScript  = 1 << 0, // '.ts', '.tsx', '.mts', '.cts'
    JavaScript  = 1 << 1, // '.js', '.jsx', '.mjs', '.cjs'
    Declaration = 1 << 2, // '.d.ts', etc.
    Json        = 1 << 3, // '.json'

    ImplementationFiles = TypeScript | JavaScript,
}

function formatExtensions(extensions: Extensions) {
    const result: string[] = [];
    if (extensions & Extensions.TypeScript) result.push("TypeScript");
    if (extensions & Extensions.JavaScript) result.push("JavaScript");
    if (extensions & Extensions.Declaration) result.push("Declaration");
    if (extensions & Extensions.Json) result.push("JSON");
    return result.join(", ");
}

function extensionsToExtensionsArray(extensions: Extensions) {
    const result: Extension[] = [];
    if (extensions & Extensions.TypeScript) result.push(...supportedTSImplementationExtensions);
    if (extensions & Extensions.JavaScript) result.push(...supportedJSExtensionsFlat);
    if (extensions & Extensions.Declaration) result.push(...supportedDeclarationExtensions);
    if (extensions & Extensions.Json) result.push(Extension.Json);
    return result;
}

interface PathAndPackageId {
    readonly fileName: string;
    readonly packageId: PackageId | undefined;
}
/** Used with `Extensions.DtsOnly` to extract the path from TypeScript results. */
function resolvedTypeScriptOnly(resolved: Resolved | undefined): PathAndPackageId | undefined {
    if (!resolved) {
        return undefined;
    }
    Debug.assert(extensionIsTS(resolved.extension));
    return { fileName: resolved.path, packageId: resolved.packageId };
}

function createResolvedModuleWithFailedLookupLocationsHandlingSymlink(
    moduleName: string,
    resolved: Resolved | undefined,
    isExternalLibraryImport: boolean | undefined,
    failedLookupLocations: string[],
    affectingLocations: string[],
    diagnostics: Diagnostic[],
    state: ModuleResolutionState,
    legacyResult?: string,
): ResolvedModuleWithFailedLookupLocations {
    // If this is from node_modules for non relative name, always respect preserveSymlinks
    if (!state.resultFromCache &&
        !state.compilerOptions.preserveSymlinks &&
        resolved &&
        isExternalLibraryImport &&
        !resolved.originalPath &&
        !isExternalModuleNameRelative(moduleName)
    ) {
        const { resolvedFileName, originalPath } = getOriginalAndResolvedFileName(resolved.path, state.host, state.traceEnabled);
        if (originalPath) resolved = { ...resolved, path: resolvedFileName, originalPath };
    }
    return createResolvedModuleWithFailedLookupLocations(
        resolved,
        isExternalLibraryImport,
        failedLookupLocations,
        affectingLocations,
        diagnostics,
        state.resultFromCache,
        legacyResult,
    );
}

function createResolvedModuleWithFailedLookupLocations(
    resolved: Resolved | undefined,
    isExternalLibraryImport: boolean | undefined,
    failedLookupLocations: string[],
    affectingLocations: string[],
    diagnostics: Diagnostic[],
    resultFromCache: ResolvedModuleWithFailedLookupLocations | undefined,
    legacyResult?: string,
): ResolvedModuleWithFailedLookupLocations {
    if (resultFromCache) {
        resultFromCache.failedLookupLocations = updateResolutionField(resultFromCache.failedLookupLocations, failedLookupLocations);
        resultFromCache.affectingLocations = updateResolutionField(resultFromCache.affectingLocations, affectingLocations);
        resultFromCache.resolutionDiagnostics = updateResolutionField(resultFromCache.resolutionDiagnostics, diagnostics);
        return resultFromCache;
    }
    return {
        resolvedModule: resolved && {
            resolvedFileName: resolved.path,
            originalPath: resolved.originalPath === true ? undefined : resolved.originalPath,
            extension: resolved.extension,
            isExternalLibraryImport,
            packageId: resolved.packageId,
            resolvedUsingTsExtension: !!resolved.resolvedUsingTsExtension,
        },
        failedLookupLocations: initializeResolutionField(failedLookupLocations),
        affectingLocations: initializeResolutionField(affectingLocations),
        resolutionDiagnostics: initializeResolutionField(diagnostics),
        node10Result: legacyResult,
    };
}
function initializeResolutionField<T>(value: T[]): T[] | undefined {
    return value.length ? value : undefined;
}
/** @internal */
export function updateResolutionField<T>(to: T[] | undefined, value: T[] | undefined) {
    if (!value?.length) return to;
    if (!to?.length) return value;
    to.push(...value);
    return to;
}

/** @internal */
export interface ModuleResolutionState {
    host: ModuleResolutionHost;
    compilerOptions: CompilerOptions;
    traceEnabled: boolean;
    failedLookupLocations: string[] | undefined;
    affectingLocations: string[] | undefined;
    resultFromCache?: ResolvedModuleWithFailedLookupLocations;
    packageJsonInfoCache: PackageJsonInfoCache | undefined;
    features: NodeResolutionFeatures;
    conditions: readonly string[];
    requestContainingDirectory: string | undefined;
    reportDiagnostic: DiagnosticReporter;
    isConfigLookup: boolean;
    candidateIsFromPackageJsonField: boolean;
}

/** Just the fields that we use for module resolution.
 *
 * @internal
 */
export interface PackageJsonPathFields {
    typings?: string;
    types?: string;
    typesVersions?: MapLike<MapLike<string[]>>;
    main?: string;
    tsconfig?: string;
    type?: string;
    imports?: object;
    exports?: object;
    name?: string;
}

interface PackageJson extends PackageJsonPathFields {
    name?: string;
    version?: string;
}

function readPackageJsonField<TMatch, K extends MatchingKeys<PackageJson, string | undefined>>(jsonContent: PackageJson, fieldName: K, typeOfTag: "string", state: ModuleResolutionState): PackageJson[K] | undefined;
function readPackageJsonField<K extends MatchingKeys<PackageJson, object | undefined>>(jsonContent: PackageJson, fieldName: K, typeOfTag: "object", state: ModuleResolutionState): PackageJson[K] | undefined;
function readPackageJsonField<K extends keyof PackageJson>(jsonContent: PackageJson, fieldName: K, typeOfTag: "string" | "object", state: ModuleResolutionState): PackageJson[K] | undefined {
    if (!hasProperty(jsonContent, fieldName)) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.package_json_does_not_have_a_0_field, fieldName);
        }
        return;
    }
    const value = jsonContent[fieldName];
    if (typeof value !== typeOfTag || value === null) { // eslint-disable-line no-null/no-null
        if (state.traceEnabled) {
            // eslint-disable-next-line no-null/no-null
            trace(state.host, Diagnostics.Expected_type_of_0_field_in_package_json_to_be_1_got_2, fieldName, typeOfTag, value === null ? "null" : typeof value);
        }
        return;
    }
    return value;
}

function readPackageJsonPathField<K extends "typings" | "types" | "main" | "tsconfig">(jsonContent: PackageJson, fieldName: K, baseDirectory: string, state: ModuleResolutionState): PackageJson[K] | undefined {
    const fileName = readPackageJsonField(jsonContent, fieldName, "string", state);
    if (fileName === undefined) {
        return;
    }
    if (!fileName) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.package_json_had_a_falsy_0_field, fieldName);
        }
        return;
    }
    const path = normalizePath(combinePaths(baseDirectory, fileName));
    if (state.traceEnabled) {
        trace(state.host, Diagnostics.package_json_has_0_field_1_that_references_2, fieldName, fileName, path);
    }
    return path;
}

function readPackageJsonTypesFields(jsonContent: PackageJson, baseDirectory: string, state: ModuleResolutionState) {
    return readPackageJsonPathField(jsonContent, "typings", baseDirectory, state)
        || readPackageJsonPathField(jsonContent, "types", baseDirectory, state);
}

function readPackageJsonTSConfigField(jsonContent: PackageJson, baseDirectory: string, state: ModuleResolutionState) {
    return readPackageJsonPathField(jsonContent, "tsconfig", baseDirectory, state);
}

function readPackageJsonMainField(jsonContent: PackageJson, baseDirectory: string, state: ModuleResolutionState) {
    return readPackageJsonPathField(jsonContent, "main", baseDirectory, state);
}

function readPackageJsonTypesVersionsField(jsonContent: PackageJson, state: ModuleResolutionState) {
    const typesVersions = readPackageJsonField(jsonContent, "typesVersions", "object", state);
    if (typesVersions === undefined) return;

    if (state.traceEnabled) {
        trace(state.host, Diagnostics.package_json_has_a_typesVersions_field_with_version_specific_path_mappings);
    }

    return typesVersions;
}

/** @internal */
export interface VersionPaths {
    version: string;
    paths: MapLike<string[]>;
}

function readPackageJsonTypesVersionPaths(jsonContent: PackageJson, state: ModuleResolutionState): VersionPaths | undefined {
    const typesVersions = readPackageJsonTypesVersionsField(jsonContent, state);
    if (typesVersions === undefined) return;

    if (state.traceEnabled) {
        for (const key in typesVersions) {
            if (hasProperty(typesVersions, key) && !VersionRange.tryParse(key)) {
                trace(state.host, Diagnostics.package_json_has_a_typesVersions_entry_0_that_is_not_a_valid_semver_range, key);
            }
        }
    }

    const result = getPackageJsonTypesVersionsPaths(typesVersions);
    if (!result) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.package_json_does_not_have_a_typesVersions_entry_that_matches_version_0, versionMajorMinor);
        }
        return;
    }

    const { version: bestVersionKey, paths: bestVersionPaths } = result;
    if (typeof bestVersionPaths !== "object") {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Expected_type_of_0_field_in_package_json_to_be_1_got_2, `typesVersions['${bestVersionKey}']`, "object", typeof bestVersionPaths);
        }
        return;
    }

    return result;
}

let typeScriptVersion: Version | undefined;

/** @internal */
export function getPackageJsonTypesVersionsPaths(typesVersions: MapLike<MapLike<string[]>>) {
    if (!typeScriptVersion) typeScriptVersion = new Version(version);

    for (const key in typesVersions) {
        if (!hasProperty(typesVersions, key)) continue;

        const keyRange = VersionRange.tryParse(key);
        if (keyRange === undefined) {
            continue;
        }

        // return the first entry whose range matches the current compiler version.
        if (keyRange.test(typeScriptVersion)) {
            return { version: key, paths: typesVersions[key] };
        }
    }
}

export function getEffectiveTypeRoots(options: CompilerOptions, host: GetEffectiveTypeRootsHost): string[] | undefined {
    if (options.typeRoots) {
        return options.typeRoots;
    }

    let currentDirectory: string | undefined;
    if (options.configFilePath) {
        currentDirectory = getDirectoryPath(options.configFilePath);
    }
    else if (host.getCurrentDirectory) {
        currentDirectory = host.getCurrentDirectory();
    }

    if (currentDirectory !== undefined) {
        return getDefaultTypeRoots(currentDirectory);
    }
}

/**
 * Returns the path to every node_modules/@types directory from some ancestor directory.
 * Returns undefined if there are none.
 */
function getDefaultTypeRoots(currentDirectory: string): string[] | undefined {
    let typeRoots: string[] | undefined;
    forEachAncestorDirectory(normalizePath(currentDirectory), directory => {
        const atTypes = combinePaths(directory, nodeModulesAtTypes);
        (typeRoots ??= []).push(atTypes);
    });
    return typeRoots;
}
const nodeModulesAtTypes = combinePaths("node_modules", "@types");

function arePathsEqual(path1: string, path2: string, host: ModuleResolutionHost): boolean {
    const useCaseSensitiveFileNames = typeof host.useCaseSensitiveFileNames === "function" ? host.useCaseSensitiveFileNames() : host.useCaseSensitiveFileNames;
    return comparePaths(path1, path2, !useCaseSensitiveFileNames) === Comparison.EqualTo;
}

function getOriginalAndResolvedFileName(fileName: string, host: ModuleResolutionHost, traceEnabled: boolean) {
    const resolvedFileName = realPath(fileName, host, traceEnabled);
    const pathsAreEqual = arePathsEqual(fileName, resolvedFileName, host);
    return {
        // If the fileName and realpath are differing only in casing prefer fileName so that we can issue correct errors for casing under forceConsistentCasingInFileNames
        resolvedFileName: pathsAreEqual ? fileName : resolvedFileName,
        originalPath: pathsAreEqual ? undefined : fileName,
    };
}

function getCandidateFromTypeRoot(typeRoot: string, typeReferenceDirectiveName: string, moduleResolutionState: ModuleResolutionState) {
    const nameForLookup = endsWith(typeRoot, "/node_modules/@types") || endsWith(typeRoot, "/node_modules/@types/") ?
        mangleScopedPackageNameWithTrace(typeReferenceDirectiveName, moduleResolutionState) :
        typeReferenceDirectiveName;
    return combinePaths(typeRoot, nameForLookup);
}

/**
 * @param {string | undefined} containingFile - file that contains type reference directive, can be undefined if containing file is unknown.
 * This is possible in case if resolution is performed for directives specified via 'types' parameter. In this case initial path for secondary lookups
 * is assumed to be the same as root directory of the project.
 */
export function resolveTypeReferenceDirective(typeReferenceDirectiveName: string, containingFile: string | undefined, options: CompilerOptions, host: ModuleResolutionHost, redirectedReference?: ResolvedProjectReference, cache?: TypeReferenceDirectiveResolutionCache, resolutionMode?: ResolutionMode): ResolvedTypeReferenceDirectiveWithFailedLookupLocations {
    Debug.assert(typeof typeReferenceDirectiveName === "string", "Non-string value passed to `ts.resolveTypeReferenceDirective`, likely by a wrapping package working with an outdated `resolveTypeReferenceDirectives` signature. This is probably not a problem in TS itself.");
    const traceEnabled = isTraceEnabled(options, host);
    if (redirectedReference) {
        options = redirectedReference.commandLine.options;
    }

    const containingDirectory = containingFile ? getDirectoryPath(containingFile) : undefined;
    let result = containingDirectory ? cache?.getFromDirectoryCache(typeReferenceDirectiveName, resolutionMode, containingDirectory, redirectedReference) : undefined;
    if (!result && containingDirectory && !isExternalModuleNameRelative(typeReferenceDirectiveName)) {
        result = cache?.getFromNonRelativeNameCache(typeReferenceDirectiveName, resolutionMode, containingDirectory, redirectedReference);
    }

    if (result) {
        if (traceEnabled) {
            trace(host, Diagnostics.Resolving_type_reference_directive_0_containing_file_1, typeReferenceDirectiveName, containingFile);
            if (redirectedReference) trace(host, Diagnostics.Using_compiler_options_of_project_reference_redirect_0, redirectedReference.sourceFile.fileName);
            trace(host, Diagnostics.Resolution_for_type_reference_directive_0_was_found_in_cache_from_location_1, typeReferenceDirectiveName, containingDirectory);
            traceResult(result);
        }
        return result;
    }


    const typeRoots = getEffectiveTypeRoots(options, host);
    if (traceEnabled) {
        if (containingFile === undefined) {
            if (typeRoots === undefined) {
                trace(host, Diagnostics.Resolving_type_reference_directive_0_containing_file_not_set_root_directory_not_set, typeReferenceDirectiveName);
            }
            else {
                trace(host, Diagnostics.Resolving_type_reference_directive_0_containing_file_not_set_root_directory_1, typeReferenceDirectiveName, typeRoots);
            }
        }
        else {
            if (typeRoots === undefined) {
                trace(host, Diagnostics.Resolving_type_reference_directive_0_containing_file_1_root_directory_not_set, typeReferenceDirectiveName, containingFile);
            }
            else {
                trace(host, Diagnostics.Resolving_type_reference_directive_0_containing_file_1_root_directory_2, typeReferenceDirectiveName, containingFile, typeRoots);
            }
        }
        if (redirectedReference) {
            trace(host, Diagnostics.Using_compiler_options_of_project_reference_redirect_0, redirectedReference.sourceFile.fileName);
        }
    }

    const failedLookupLocations: string[] = [];
    const affectingLocations: string[] = [];
    let features = getNodeResolutionFeatures(options);
    // Unlike `import` statements, whose mode-calculating APIs are all guaranteed to return `undefined` if we're in an un-mode-ed module resolution
    // setting, type references will return their target mode regardless of options because of how the parser works, so we guard against the mode being
    // set in a non-modal module resolution setting here. Do note that our behavior is not particularly well defined when these mode-overriding imports
    // are present in a non-modal project; while in theory we'd like to either ignore the mode or provide faithful modern resolution, depending on what we feel is best,
    // in practice, not every cache has the options available to intelligently make the choice to ignore the mode request, and it's unclear how modern "faithful modern
    // resolution" should be (`node16`? `nodenext`?). As such, witnessing a mode-overriding triple-slash reference in a non-modal module resolution
    // context should _probably_ be an error - and that should likely be handled by the `Program` (which is what we do).
    if (resolutionMode === ModuleKind.ESNext && (getEmitModuleResolutionKind(options) === ModuleResolutionKind.Node16 || getEmitModuleResolutionKind(options) === ModuleResolutionKind.NodeNext)) {
        features |= NodeResolutionFeatures.EsmMode;
    }
    const conditions = features & NodeResolutionFeatures.Exports ? getConditions(options, !!(features & NodeResolutionFeatures.EsmMode)) : [];
    const diagnostics: Diagnostic[] = [];
    const moduleResolutionState: ModuleResolutionState = {
        compilerOptions: options,
        host,
        traceEnabled,
        failedLookupLocations,
        affectingLocations,
        packageJsonInfoCache: cache,
        features,
        conditions,
        requestContainingDirectory: containingDirectory,
        reportDiagnostic: diag => void diagnostics.push(diag),
        isConfigLookup: false,
        candidateIsFromPackageJsonField: false,
    };
    let resolved = primaryLookup();
    let primary = true;
    if (!resolved) {
        resolved = secondaryLookup();
        primary = false;
    }

    let resolvedTypeReferenceDirective: ResolvedTypeReferenceDirective | undefined;
    if (resolved) {
        const { fileName, packageId } = resolved;
        let resolvedFileName = fileName, originalPath: string | undefined;
        if (!options.preserveSymlinks) ({ resolvedFileName, originalPath } = getOriginalAndResolvedFileName(fileName, host, traceEnabled));
        resolvedTypeReferenceDirective = {
            primary,
            resolvedFileName,
            originalPath,
            packageId,
            isExternalLibraryImport: pathContainsNodeModules(fileName),
        };
    }
    result = {
        resolvedTypeReferenceDirective,
        failedLookupLocations: initializeResolutionField(failedLookupLocations),
        affectingLocations: initializeResolutionField(affectingLocations),
        resolutionDiagnostics: initializeResolutionField(diagnostics),
    };
    if (containingDirectory) {
        cache?.getOrCreateCacheForDirectory(containingDirectory, redirectedReference).set(typeReferenceDirectiveName, /*mode*/ resolutionMode, result);
        if (!isExternalModuleNameRelative(typeReferenceDirectiveName)) {
            cache?.getOrCreateCacheForNonRelativeName(typeReferenceDirectiveName, resolutionMode, redirectedReference).set(containingDirectory, result);
        }
    }
    if (traceEnabled) traceResult(result);
    return result;

    function traceResult(result: ResolvedTypeReferenceDirectiveWithFailedLookupLocations) {
        if (!result.resolvedTypeReferenceDirective?.resolvedFileName) {
            trace(host, Diagnostics.Type_reference_directive_0_was_not_resolved, typeReferenceDirectiveName);
        }
        else if (result.resolvedTypeReferenceDirective.packageId) {
            trace(host, Diagnostics.Type_reference_directive_0_was_successfully_resolved_to_1_with_Package_ID_2_primary_Colon_3, typeReferenceDirectiveName, result.resolvedTypeReferenceDirective.resolvedFileName, packageIdToString(result.resolvedTypeReferenceDirective.packageId), result.resolvedTypeReferenceDirective.primary);
        }
        else {
            trace(host, Diagnostics.Type_reference_directive_0_was_successfully_resolved_to_1_primary_Colon_2, typeReferenceDirectiveName, result.resolvedTypeReferenceDirective.resolvedFileName, result.resolvedTypeReferenceDirective.primary);
        }
    }

    function primaryLookup(): PathAndPackageId | undefined {
        // Check primary library paths
        if (typeRoots && typeRoots.length) {
            if (traceEnabled) {
                trace(host, Diagnostics.Resolving_with_primary_search_path_0, typeRoots.join(", "));
            }
            return firstDefined(typeRoots, typeRoot => {
                const candidate = getCandidateFromTypeRoot(typeRoot, typeReferenceDirectiveName, moduleResolutionState);
                const directoryExists = directoryProbablyExists(typeRoot, host);
                if (!directoryExists && traceEnabled) {
                    trace(host, Diagnostics.Directory_0_does_not_exist_skipping_all_lookups_in_it, typeRoot);
                }
                if (options.typeRoots) {
                    // Custom typeRoots resolve as file or directory just like we do modules
                    const resolvedFromFile = loadModuleFromFile(Extensions.Declaration, candidate, !directoryExists, moduleResolutionState);
                    if (resolvedFromFile) {
                        const packageDirectory = parseNodeModuleFromPath(resolvedFromFile.path);
                        const packageInfo = packageDirectory ? getPackageJsonInfo(packageDirectory, /*onlyRecordFailures*/ false, moduleResolutionState) : undefined;
                        return resolvedTypeScriptOnly(withPackageId(packageInfo, resolvedFromFile));
                    }
                }
                return resolvedTypeScriptOnly(
                    loadNodeModuleFromDirectory(Extensions.Declaration, candidate,
                        !directoryExists, moduleResolutionState));
            });
        }
        else {
            if (traceEnabled) {
                trace(host, Diagnostics.Root_directory_cannot_be_determined_skipping_primary_search_paths);
            }
        }
    }

    function secondaryLookup(): PathAndPackageId | undefined {
        const initialLocationForSecondaryLookup = containingFile && getDirectoryPath(containingFile);
        if (initialLocationForSecondaryLookup !== undefined) {
            let result: Resolved | undefined;
            if (!options.typeRoots || !endsWith(containingFile!, inferredTypesContainingFile)) {
                // check secondary locations
                if (traceEnabled) {
                    trace(host, Diagnostics.Looking_up_in_node_modules_folder_initial_location_0, initialLocationForSecondaryLookup);
                }
                if (!isExternalModuleNameRelative(typeReferenceDirectiveName)) {
                    const searchResult = loadModuleFromNearestNodeModulesDirectory(Extensions.Declaration, typeReferenceDirectiveName, initialLocationForSecondaryLookup, moduleResolutionState, /*cache*/ undefined, /*redirectedReference*/ undefined);
                    result = searchResult && searchResult.value;
                }
                else {
                    const { path: candidate } = normalizePathForCJSResolution(initialLocationForSecondaryLookup, typeReferenceDirectiveName);
                    result = nodeLoadModuleByRelativeName(Extensions.Declaration, candidate, /*onlyRecordFailures*/ false, moduleResolutionState, /*considerPackageJson*/ true);
                }
            }
            else if (traceEnabled) {
                trace(host, Diagnostics.Resolving_type_reference_directive_for_program_that_specifies_custom_typeRoots_skipping_lookup_in_node_modules_folder);
            }
            return resolvedTypeScriptOnly(result);
        }
        else {
            if (traceEnabled) {
                trace(host, Diagnostics.Containing_file_is_not_specified_and_root_directory_cannot_be_determined_skipping_lookup_in_node_modules_folder);
            }
        }
    }
}

function getNodeResolutionFeatures(options: CompilerOptions) {
    let features = NodeResolutionFeatures.None;
    switch (getEmitModuleResolutionKind(options)) {
        case ModuleResolutionKind.Node16:
            features = NodeResolutionFeatures.Node16Default;
            break;
        case ModuleResolutionKind.NodeNext:
            features = NodeResolutionFeatures.NodeNextDefault;
            break;
        case ModuleResolutionKind.Bundler:
            features = NodeResolutionFeatures.BundlerDefault;
            break;
    }
    if (options.resolvePackageJsonExports) {
        features |= NodeResolutionFeatures.Exports;
    }
    else if (options.resolvePackageJsonExports === false) {
        features &= ~NodeResolutionFeatures.Exports;
    }
    if (options.resolvePackageJsonImports) {
        features |= NodeResolutionFeatures.Imports;
    }
    else if (options.resolvePackageJsonImports === false) {
        features &= ~NodeResolutionFeatures.Imports;
    }
    return features;
}

/** @internal */
export function getConditions(options: CompilerOptions, esmMode?: boolean) {
    // conditions are only used by the node16/nodenext/bundler resolvers - there's no priority order in the list,
    // it's essentially a set (priority is determined by object insertion order in the object we look at).
    const conditions = esmMode || getEmitModuleResolutionKind(options) === ModuleResolutionKind.Bundler
        ? ["import"]
        : ["require"];
    if (!options.noDtsResolution) {
        conditions.push("types");
    }
    if (getEmitModuleResolutionKind(options) !== ModuleResolutionKind.Bundler) {
        conditions.push("node");
    }
    return concatenate(conditions, options.customConditions);
}

/**
 * @internal
 * Does not try `@types/${packageName}` - use a second pass if needed.
 */
export function resolvePackageNameToPackageJson(
    packageName: string,
    containingDirectory: string,
    options: CompilerOptions,
    host: ModuleResolutionHost,
    cache: ModuleResolutionCache | undefined,
): PackageJsonInfo | undefined {
    const moduleResolutionState = getTemporaryModuleResolutionState(cache?.getPackageJsonInfoCache(), host, options);

    return forEachAncestorDirectory(containingDirectory, ancestorDirectory => {
        if (getBaseFileName(ancestorDirectory) !== "node_modules") {
            const nodeModulesFolder = combinePaths(ancestorDirectory, "node_modules");
            const candidate = combinePaths(nodeModulesFolder, packageName);
            return getPackageJsonInfo(candidate, /*onlyRecordFailures*/ false, moduleResolutionState);
        }
    });
}

/**
 * Given a set of options, returns the set of type directive names
 *   that should be included for this program automatically.
 * This list could either come from the config file,
 *   or from enumerating the types root + initial secondary types lookup location.
 * More type directives might appear in the program later as a result of loading actual source files;
 *   this list is only the set of defaults that are implicitly included.
 */
export function getAutomaticTypeDirectiveNames(options: CompilerOptions, host: ModuleResolutionHost): string[] {
    // Use explicit type list from tsconfig.json
    if (options.types) {
        return options.types;
    }

    // Walk the primary type lookup locations
    const result: string[] = [];
    if (host.directoryExists && host.getDirectories) {
        const typeRoots = getEffectiveTypeRoots(options, host);
        if (typeRoots) {
            for (const root of typeRoots) {
                if (host.directoryExists(root)) {
                    for (const typeDirectivePath of host.getDirectories(root)) {
                        const normalized = normalizePath(typeDirectivePath);
                        const packageJsonPath = combinePaths(root, normalized, "package.json");
                        // `types-publisher` sometimes creates packages with `"typings": null` for packages that don't provide their own types.
                        // See `createNotNeededPackageJSON` in the types-publisher` repo.
                        // eslint-disable-next-line no-null/no-null
                        const isNotNeededPackage = host.fileExists(packageJsonPath) && (readJson(packageJsonPath, host) as PackageJson).typings === null;
                        if (!isNotNeededPackage) {
                            const baseFileName = getBaseFileName(normalized);

                            // At this stage, skip results with leading dot.
                            if (baseFileName.charCodeAt(0) !== CharacterCodes.dot) {
                                // Return just the type directive names
                                result.push(baseFileName);
                            }
                        }
                    }
                }
            }
        }
    }
    return result;
}

export interface TypeReferenceDirectiveResolutionCache extends PerDirectoryResolutionCache<ResolvedTypeReferenceDirectiveWithFailedLookupLocations>, NonRelativeNameResolutionCache<ResolvedTypeReferenceDirectiveWithFailedLookupLocations>, PackageJsonInfoCache {
    /** @internal */ clearAllExceptPackageJsonInfoCache(): void;
}

export interface ModeAwareCache<T> {
    get(key: string, mode: ResolutionMode): T | undefined;
    set(key: string, mode: ResolutionMode, value: T): this;
    delete(key: string, mode: ResolutionMode): this;
    has(key: string, mode: ResolutionMode): boolean;
    forEach(cb: (elem: T, key: string, mode: ResolutionMode) => void): void;
    size(): number;
}

/**
 * Cached resolutions per containing directory.
 * This assumes that any module id will have the same resolution for sibling files located in the same folder.
 */
export interface PerDirectoryResolutionCache<T> {
    getFromDirectoryCache(name: string, mode: ResolutionMode, directoryName: string, redirectedReference: ResolvedProjectReference | undefined): T | undefined;
    getOrCreateCacheForDirectory(directoryName: string, redirectedReference?: ResolvedProjectReference): ModeAwareCache<T>;
    clear(): void;
    /**
     *  Updates with the current compilerOptions the cache will operate with.
     *  This updates the redirects map as well if needed so module resolutions are cached if they can across the projects
     */
    update(options: CompilerOptions): void;
}

export interface NonRelativeNameResolutionCache<T> {
    getFromNonRelativeNameCache(nonRelativeName: string, mode: ResolutionMode, directoryName: string, redirectedReference: ResolvedProjectReference | undefined): T | undefined;
    getOrCreateCacheForNonRelativeName(nonRelativeName: string, mode: ResolutionMode, redirectedReference?: ResolvedProjectReference): PerNonRelativeNameCache<T>;
    clear(): void;
    /**
     *  Updates with the current compilerOptions the cache will operate with.
     *  This updates the redirects map as well if needed so module resolutions are cached if they can across the projects
     */
    update(options: CompilerOptions): void;
}

export interface PerNonRelativeNameCache<T> {
    get(directory: string): T | undefined;
    set(directory: string, result: T): void;
}

export interface ModuleResolutionCache extends PerDirectoryResolutionCache<ResolvedModuleWithFailedLookupLocations>, NonRelativeModuleNameResolutionCache, PackageJsonInfoCache {
    getPackageJsonInfoCache(): PackageJsonInfoCache;
    /** @internal */ clearAllExceptPackageJsonInfoCache(): void;
}

/**
 * Stored map from non-relative module name to a table: directory -> result of module lookup in this directory
 * We support only non-relative module names because resolution of relative module names is usually more deterministic and thus less expensive.
 */
export interface NonRelativeModuleNameResolutionCache extends NonRelativeNameResolutionCache<ResolvedModuleWithFailedLookupLocations>, PackageJsonInfoCache {
    /** @deprecated Use getOrCreateCacheForNonRelativeName */
    getOrCreateCacheForModuleName(nonRelativeModuleName: string, mode: ResolutionMode, redirectedReference?: ResolvedProjectReference): PerModuleNameCache;
}

export interface PackageJsonInfoCache {
    /** @internal */ getPackageJsonInfo(packageJsonPath: string): PackageJsonInfo | boolean | undefined;
    /** @internal */ setPackageJsonInfo(packageJsonPath: string, info: PackageJsonInfo | boolean): void;
    /** @internal */ entries(): [Path, PackageJsonInfo | boolean][];
    /** @internal */ getInternalMap(): Map<Path, PackageJsonInfo | boolean> | undefined;
    clear(): void;
}

export type PerModuleNameCache = PerNonRelativeNameCache<ResolvedModuleWithFailedLookupLocations>;

function compilerOptionValueToString(value: unknown): string {
    if (value === null || typeof value !== "object") { // eslint-disable-line no-null/no-null
        return "" + value;
    }
    if (isArray(value)) {
        return `[${value.map(e => compilerOptionValueToString(e))?.join(",")}]`;
    }
    let str = "{";
    for (const key in value) {
        if (hasProperty(value, key)) {
            str += `${key}: ${compilerOptionValueToString((value as any)[key])}`;
        }
    }
    return str + "}";
}

/** @internal */
export function getKeyForCompilerOptions(options: CompilerOptions, affectingOptionDeclarations: readonly CommandLineOption[]) {
    return affectingOptionDeclarations.map(option => compilerOptionValueToString(getCompilerOptionValue(options, option))).join("|") + `|${options.pathsBasePath}`;
}

/** @internal */
export interface CacheWithRedirects<K, V> {
    getMapOfCacheRedirects(redirectedReference: ResolvedProjectReference | undefined): Map<K, V> | undefined;
    getOrCreateMapOfCacheRedirects(redirectedReference: ResolvedProjectReference | undefined): Map<K, V>;
    update(newOptions: CompilerOptions): void;
    clear(): void;
}

/** @internal */
export function createCacheWithRedirects<K, V>(ownOptions: CompilerOptions | undefined): CacheWithRedirects<K, V> {
    type RedirectsCacheKey = string & { __compilerOptionsKey: any; };
    const redirectsMap = new Map<CompilerOptions, Map<K, V>>();
    const optionsToRedirectsKey = new Map<CompilerOptions, RedirectsCacheKey>();
    const redirectsKeyToMap = new Map<RedirectsCacheKey, Map<K, V>>();
    let ownMap = new Map<K, V>();
    if (ownOptions) redirectsMap.set(ownOptions, ownMap);
    return {
        getMapOfCacheRedirects,
        getOrCreateMapOfCacheRedirects,
        update,
        clear,
    };

    function getMapOfCacheRedirects(redirectedReference: ResolvedProjectReference | undefined): Map<K, V> | undefined {
        return redirectedReference ?
            getOrCreateMap(redirectedReference.commandLine.options, /*create*/ false) :
            ownMap;
    }

    function getOrCreateMapOfCacheRedirects(redirectedReference: ResolvedProjectReference | undefined): Map<K, V> {
        return redirectedReference ?
            getOrCreateMap(redirectedReference.commandLine.options, /*create*/ true) :
            ownMap;
    }

    function update(newOptions: CompilerOptions) {
        if (ownOptions !== newOptions) {
            if (ownOptions) ownMap = getOrCreateMap(newOptions, /*create*/ true); // set new map for new options as ownMap
            else redirectsMap.set(newOptions, ownMap); // Use existing map if oldOptions = undefined
            ownOptions = newOptions;
        }
    }

    function getOrCreateMap(redirectOptions: CompilerOptions, create: true): Map<K, V>;
    function getOrCreateMap(redirectOptions: CompilerOptions, create: false): Map<K, V> | undefined;
    function getOrCreateMap(redirectOptions: CompilerOptions, create: boolean): Map<K, V> | undefined {
        let result = redirectsMap.get(redirectOptions);
        if (result) return result;
        const key = getRedirectsCacheKey(redirectOptions);
        result = redirectsKeyToMap.get(key);
        if (!result) {
            if (ownOptions) {
                const ownKey = getRedirectsCacheKey(ownOptions);
                if (ownKey === key) result = ownMap;
                else if (!redirectsKeyToMap.has(ownKey)) redirectsKeyToMap.set(ownKey, ownMap);
            }
            if (create) result ??= new Map();
            if (result) redirectsKeyToMap.set(key, result);
        }
        if (result) redirectsMap.set(redirectOptions, result);
        return result;
    }

    function clear() {
        const ownKey = ownOptions && optionsToRedirectsKey.get(ownOptions);
        ownMap.clear();
        redirectsMap.clear();
        optionsToRedirectsKey.clear();
        redirectsKeyToMap.clear();
        if (ownOptions) {
            if (ownKey) optionsToRedirectsKey.set(ownOptions, ownKey);
            redirectsMap.set(ownOptions, ownMap);
        }
    }

    function getRedirectsCacheKey(options: CompilerOptions) {
        let result = optionsToRedirectsKey.get(options);
        if (!result) {
            optionsToRedirectsKey.set(options, result = getKeyForCompilerOptions(options, moduleResolutionOptionDeclarations) as RedirectsCacheKey);
        }
        return result;
    }
}

function createPackageJsonInfoCache(currentDirectory: string, getCanonicalFileName: (s: string) => string): PackageJsonInfoCache {
    let cache: Map<Path, PackageJsonInfo | boolean> | undefined;
    return { getPackageJsonInfo, setPackageJsonInfo, clear, entries, getInternalMap };
    function getPackageJsonInfo(packageJsonPath: string) {
        return cache?.get(toPath(packageJsonPath, currentDirectory, getCanonicalFileName));
    }
    function setPackageJsonInfo(packageJsonPath: string, info: PackageJsonInfo | boolean) {
        (cache ||= new Map()).set(toPath(packageJsonPath, currentDirectory, getCanonicalFileName), info);
    }
    function clear() {
        cache = undefined;
    }
    function entries() {
        const iter = cache?.entries();
        return iter ? arrayFrom(iter) : [];
    }
    function getInternalMap() {
        return cache;
    }
}

function getOrCreateCache<K, V>(cacheWithRedirects: CacheWithRedirects<K, V>, redirectedReference: ResolvedProjectReference | undefined, key: K, create: () => V): V {
    const cache = cacheWithRedirects.getOrCreateMapOfCacheRedirects(redirectedReference);
    let result = cache.get(key);
    if (!result) {
        result = create();
        cache.set(key, result);
    }
    return result;
}

function createPerDirectoryResolutionCache<T>(currentDirectory: string, getCanonicalFileName: GetCanonicalFileName, options: CompilerOptions | undefined): PerDirectoryResolutionCache<T> {
    const directoryToModuleNameMap = createCacheWithRedirects<Path, ModeAwareCache<T>>(options);
    return {
        getFromDirectoryCache,
        getOrCreateCacheForDirectory,
        clear,
        update,
    };

    function clear() {
        directoryToModuleNameMap.clear();
    }

    function update(options: CompilerOptions) {
        directoryToModuleNameMap.update(options);
    }

    function getOrCreateCacheForDirectory(directoryName: string, redirectedReference?: ResolvedProjectReference) {
        const path = toPath(directoryName, currentDirectory, getCanonicalFileName);
        return getOrCreateCache(directoryToModuleNameMap, redirectedReference, path, () => createModeAwareCache());
    }

    function getFromDirectoryCache(name: string, mode: ResolutionMode, directoryName: string, redirectedReference: ResolvedProjectReference | undefined) {
        const path = toPath(directoryName, currentDirectory, getCanonicalFileName);
        return directoryToModuleNameMap.getMapOfCacheRedirects(redirectedReference)?.get(path)?.get(name, mode);
    }
}

/** @internal */
export type ModeAwareCacheKey = string & { __modeAwareCacheKey: any; };
/** @internal */
export function createModeAwareCacheKey(specifier: string, mode: ResolutionMode) {
    return (mode === undefined ? specifier : `${mode}|${specifier}`) as ModeAwareCacheKey;
}
/** @internal */
export function createModeAwareCache<T>(): ModeAwareCache<T> {
    const underlying = new Map<ModeAwareCacheKey, T>();
    const memoizedReverseKeys = new Map<ModeAwareCacheKey, [specifier: string, mode: ResolutionMode]>();

    const cache: ModeAwareCache<T> = {
        get(specifier, mode) {
            return underlying.get(getUnderlyingCacheKey(specifier, mode));
        },
        set(specifier, mode, value) {
            underlying.set(getUnderlyingCacheKey(specifier, mode), value);
            return cache;
        },
        delete(specifier, mode) {
            underlying.delete(getUnderlyingCacheKey(specifier, mode));
            return cache;
        },
        has(specifier, mode) {
            return underlying.has(getUnderlyingCacheKey(specifier, mode));
        },
        forEach(cb) {
            return underlying.forEach((elem, key) => {
                const [specifier, mode] = memoizedReverseKeys.get(key)!;
                return cb(elem, specifier, mode);
            });
        },
        size() {
            return underlying.size;
        }
    };
    return cache;

    function getUnderlyingCacheKey(specifier: string, mode: ResolutionMode) {
        const result = createModeAwareCacheKey(specifier, mode);
        memoizedReverseKeys.set(result, [specifier, mode]);
        return result;
    }
}

/** @internal */
export function zipToModeAwareCache<K, V>(
    file: SourceFile,
    keys: readonly K[],
    values: readonly V[],
    nameAndModeGetter: ResolutionNameAndModeGetter<K, SourceFile>,
): ModeAwareCache<V> {
    Debug.assert(keys.length === values.length);
    const map = createModeAwareCache<V>();
    for (let i = 0; i < keys.length; ++i) {
        const entry = keys[i];
        map.set(nameAndModeGetter.getName(entry), nameAndModeGetter.getMode(entry, file), values[i]);
    }
    return map;
}

function getOriginalOrResolvedModuleFileName(result: ResolvedModuleWithFailedLookupLocations) {
    return result.resolvedModule && (result.resolvedModule.originalPath || result.resolvedModule.resolvedFileName);
}

function getOriginalOrResolvedTypeReferenceFileName(result: ResolvedTypeReferenceDirectiveWithFailedLookupLocations) {
    return result.resolvedTypeReferenceDirective &&
        (result.resolvedTypeReferenceDirective.originalPath || result.resolvedTypeReferenceDirective.resolvedFileName);
}

function createNonRelativeNameResolutionCache<T>(
    currentDirectory: string,
    getCanonicalFileName: (s: string) => string,
    options: CompilerOptions | undefined,
    getResolvedFileName: (result: T) => string | undefined,
): NonRelativeNameResolutionCache<T> {
    const moduleNameToDirectoryMap = createCacheWithRedirects<ModeAwareCacheKey, PerNonRelativeNameCache<T>>(options);
    return {
        getFromNonRelativeNameCache,
        getOrCreateCacheForNonRelativeName,
        clear,
        update,
    };

    function clear() {
        moduleNameToDirectoryMap.clear();
    }

    function update(options: CompilerOptions) {
        moduleNameToDirectoryMap.update(options);
    }

    function getFromNonRelativeNameCache(nonRelativeModuleName: string, mode: ResolutionMode, directoryName: string, redirectedReference?: ResolvedProjectReference): T | undefined {
        Debug.assert(!isExternalModuleNameRelative(nonRelativeModuleName));
        return moduleNameToDirectoryMap.getMapOfCacheRedirects(redirectedReference)?.get(createModeAwareCacheKey(nonRelativeModuleName, mode))?.get(directoryName);
    }

    function getOrCreateCacheForNonRelativeName(nonRelativeModuleName: string, mode: ResolutionMode, redirectedReference?: ResolvedProjectReference): PerNonRelativeNameCache<T> {
        Debug.assert(!isExternalModuleNameRelative(nonRelativeModuleName));
        return getOrCreateCache(moduleNameToDirectoryMap, redirectedReference, createModeAwareCacheKey(nonRelativeModuleName, mode), createPerModuleNameCache);
    }

    function createPerModuleNameCache(): PerNonRelativeNameCache<T> {
        const directoryPathMap = new Map<Path, T>();

        return { get, set };

        function get(directory: string): T | undefined {
            return directoryPathMap.get(toPath(directory, currentDirectory, getCanonicalFileName));
        }

        /**
         * At first this function add entry directory -> module resolution result to the table.
         * Then it computes the set of parent folders for 'directory' that should have the same module resolution result
         * and for every parent folder in set it adds entry: parent -> module resolution. .
         * Lets say we first directory name: /a/b/c/d/e and resolution result is: /a/b/bar.ts.
         * Set of parent folders that should have the same result will be:
         * [
         *     /a/b/c/d, /a/b/c, /a/b
         * ]
         * this means that request for module resolution from file in any of these folder will be immediately found in cache.
         */
        function set(directory: string, result: T): void {
            const path = toPath(directory, currentDirectory, getCanonicalFileName);
            // if entry is already in cache do nothing
            if (directoryPathMap.has(path)) {
                return;
            }
            directoryPathMap.set(path, result);

            const resolvedFileName = getResolvedFileName(result);
            // find common prefix between directory and resolved file name
            // this common prefix should be the shortest path that has the same resolution
            // directory: /a/b/c/d/e
            // resolvedFileName: /a/b/foo.d.ts
            // commonPrefix: /a/b
            // for failed lookups cache the result for every directory up to root
            const commonPrefix = resolvedFileName && getCommonPrefix(path, resolvedFileName);
            let current = path;
            while (current !== commonPrefix) {
                const parent = getDirectoryPath(current);
                if (parent === current || directoryPathMap.has(parent)) {
                    break;
                }
                directoryPathMap.set(parent, result);
                current = parent;
            }
        }

        function getCommonPrefix(directory: Path, resolution: string) {
            const resolutionDirectory = toPath(getDirectoryPath(resolution), currentDirectory, getCanonicalFileName);

            // find first position where directory and resolution differs
            let i = 0;
            const limit = Math.min(directory.length, resolutionDirectory.length);
            while (i < limit && directory.charCodeAt(i) === resolutionDirectory.charCodeAt(i)) {
                i++;
            }
            if (i === directory.length && (resolutionDirectory.length === i || resolutionDirectory[i] === directorySeparator)) {
                return directory;
            }
            const rootLength = getRootLength(directory);
            if (i < rootLength) {
                return undefined;
            }
            const sep = directory.lastIndexOf(directorySeparator, i - 1);
            if (sep === -1) {
                return undefined;
            }
            return directory.substr(0, Math.max(sep, rootLength));
        }
    }
}

interface ModuleOrTypeReferenceResolutionCache<T> extends PerDirectoryResolutionCache<T>, NonRelativeNameResolutionCache<T>, PackageJsonInfoCache {
    getPackageJsonInfoCache(): PackageJsonInfoCache;
    clearAllExceptPackageJsonInfoCache(): void;
}
function createModuleOrTypeReferenceResolutionCache<T>(
    currentDirectory: string,
    getCanonicalFileName: (s: string) => string,
    options: CompilerOptions | undefined,
    packageJsonInfoCache: PackageJsonInfoCache | undefined,
    getResolvedFileName: (result: T) => string | undefined,
): ModuleOrTypeReferenceResolutionCache<T> {
    const perDirectoryResolutionCache = createPerDirectoryResolutionCache<T>(currentDirectory, getCanonicalFileName, options);
    const nonRelativeNameResolutionCache = createNonRelativeNameResolutionCache(
        currentDirectory,
        getCanonicalFileName,
        options,
        getResolvedFileName,
    );
    packageJsonInfoCache ??= createPackageJsonInfoCache(currentDirectory, getCanonicalFileName);

    return {
        ...packageJsonInfoCache,
        ...perDirectoryResolutionCache,
        ...nonRelativeNameResolutionCache,
        clear,
        update,
        getPackageJsonInfoCache: () => packageJsonInfoCache!,
        clearAllExceptPackageJsonInfoCache,
    };

    function clear() {
        clearAllExceptPackageJsonInfoCache();
        packageJsonInfoCache!.clear();
    }

    function clearAllExceptPackageJsonInfoCache() {
        perDirectoryResolutionCache.clear();
        nonRelativeNameResolutionCache.clear();
    }

    function update(options: CompilerOptions) {
        perDirectoryResolutionCache.update(options);
        nonRelativeNameResolutionCache.update(options);
    }
}

export function createModuleResolutionCache(
    currentDirectory: string,
    getCanonicalFileName: (s: string) => string,
    options?: CompilerOptions,
    packageJsonInfoCache?: PackageJsonInfoCache,
): ModuleResolutionCache {
    const result = createModuleOrTypeReferenceResolutionCache(
        currentDirectory,
        getCanonicalFileName,
        options,
        packageJsonInfoCache,
        getOriginalOrResolvedModuleFileName,
    ) as ModuleResolutionCache;
    result.getOrCreateCacheForModuleName = (nonRelativeName, mode, redirectedReference) => result.getOrCreateCacheForNonRelativeName(nonRelativeName, mode, redirectedReference);
    return result;
}

export function createTypeReferenceDirectiveResolutionCache(
    currentDirectory: string,
    getCanonicalFileName: (s: string) => string,
    options?: CompilerOptions,
    packageJsonInfoCache?: PackageJsonInfoCache,
): TypeReferenceDirectiveResolutionCache {
    return createModuleOrTypeReferenceResolutionCache(
        currentDirectory,
        getCanonicalFileName,
        options,
        packageJsonInfoCache,
        getOriginalOrResolvedTypeReferenceFileName
    );
}

/** @internal */
export function getOptionsForLibraryResolution(options: CompilerOptions) {
    return { moduleResolution: ModuleResolutionKind.Node10, traceResolution: options.traceResolution };
}

/** @internal */
export function resolveLibrary(libraryName: string, resolveFrom: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache): ResolvedModuleWithFailedLookupLocations {
    return resolveModuleName(libraryName, resolveFrom, getOptionsForLibraryResolution(compilerOptions), host, cache);
}

export function resolveModuleNameFromCache(moduleName: string, containingFile: string, cache: ModuleResolutionCache, mode?: ResolutionMode): ResolvedModuleWithFailedLookupLocations | undefined {
    const containingDirectory = getDirectoryPath(containingFile);
    return cache.getFromDirectoryCache(moduleName, mode, containingDirectory, /*redirectedReference*/ undefined);
}

export function resolveModuleName(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference, resolutionMode?: ResolutionMode): ResolvedModuleWithFailedLookupLocations {
    const traceEnabled = isTraceEnabled(compilerOptions, host);
    if (redirectedReference) {
        compilerOptions = redirectedReference.commandLine.options;
    }
    if (traceEnabled) {
        trace(host, Diagnostics.Resolving_module_0_from_1, moduleName, containingFile);
        if (redirectedReference) {
            trace(host, Diagnostics.Using_compiler_options_of_project_reference_redirect_0, redirectedReference.sourceFile.fileName);
        }
    }
    const containingDirectory = getDirectoryPath(containingFile);
    let result = cache?.getFromDirectoryCache(moduleName, resolutionMode, containingDirectory, redirectedReference);

    if (result) {
        if (traceEnabled) {
            trace(host, Diagnostics.Resolution_for_module_0_was_found_in_cache_from_location_1, moduleName, containingDirectory);
        }
    }
    else {
        let moduleResolution = compilerOptions.moduleResolution;
        if (moduleResolution === undefined) {
            switch (getEmitModuleKind(compilerOptions)) {
                case ModuleKind.CommonJS:
                    moduleResolution = ModuleResolutionKind.Node10;
                    break;
                case ModuleKind.Node16:
                    moduleResolution = ModuleResolutionKind.Node16;
                    break;
                case ModuleKind.NodeNext:
                    moduleResolution = ModuleResolutionKind.NodeNext;
                    break;
                default:
                    moduleResolution = ModuleResolutionKind.Classic;
                    break;
            }
            if (traceEnabled) {
                trace(host, Diagnostics.Module_resolution_kind_is_not_specified_using_0, ModuleResolutionKind[moduleResolution]);
            }
        }
        else {
            if (traceEnabled) {
                trace(host, Diagnostics.Explicitly_specified_module_resolution_kind_Colon_0, ModuleResolutionKind[moduleResolution]);
            }
        }

        perfLogger?.logStartResolveModule(moduleName /* , containingFile, ModuleResolutionKind[moduleResolution]*/);
        switch (moduleResolution) {
            case ModuleResolutionKind.Node16:
                result = node16ModuleNameResolver(moduleName, containingFile, compilerOptions, host, cache, redirectedReference, resolutionMode);
                break;
            case ModuleResolutionKind.NodeNext:
                result = nodeNextModuleNameResolver(moduleName, containingFile, compilerOptions, host, cache, redirectedReference, resolutionMode);
                break;
            case ModuleResolutionKind.Node10:
                result = nodeModuleNameResolver(moduleName, containingFile, compilerOptions, host, cache, redirectedReference);
                break;
            case ModuleResolutionKind.Classic:
                result = classicNameResolver(moduleName, containingFile, compilerOptions, host, cache, redirectedReference);
                break;
            case ModuleResolutionKind.Bundler:
                result = bundlerModuleNameResolver(moduleName, containingFile, compilerOptions, host, cache, redirectedReference);
                break;
            default:
                return Debug.fail(`Unexpected moduleResolution: ${moduleResolution}`);
        }
        if (result && result.resolvedModule) perfLogger?.logInfoEvent(`Module "${moduleName}" resolved to "${result.resolvedModule.resolvedFileName}"`);
        perfLogger?.logStopResolveModule((result && result.resolvedModule) ? "" + result.resolvedModule.resolvedFileName : "null");

        cache?.getOrCreateCacheForDirectory(containingDirectory, redirectedReference).set(moduleName, resolutionMode, result);
        if (!isExternalModuleNameRelative(moduleName)) {
            // put result in per-module name cache
            cache?.getOrCreateCacheForNonRelativeName(moduleName, resolutionMode, redirectedReference).set(containingDirectory, result);
        }
    }

    if (traceEnabled) {
        if (result.resolvedModule) {
            if (result.resolvedModule.packageId) {
                trace(host, Diagnostics.Module_name_0_was_successfully_resolved_to_1_with_Package_ID_2, moduleName, result.resolvedModule.resolvedFileName, packageIdToString(result.resolvedModule.packageId));
            }
            else {
                trace(host, Diagnostics.Module_name_0_was_successfully_resolved_to_1, moduleName, result.resolvedModule.resolvedFileName);
            }
        }
        else {
            trace(host, Diagnostics.Module_name_0_was_not_resolved, moduleName);
        }
    }

    return result;
}

/*
 * Every module resolution kind can has its specific understanding how to load module from a specific path on disk
 * I.e. for path '/a/b/c':
 * - Node loader will first to try to check if '/a/b/c' points to a file with some supported extension and if this fails
 * it will try to load module from directory: directory '/a/b/c' should exist and it should have either 'package.json' with
 * 'typings' entry or file 'index' with some supported extension
 * - Classic loader will only try to interpret '/a/b/c' as file.
 */
type ResolutionKindSpecificLoader = (extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState) => Resolved | undefined;

/**
 * Any module resolution kind can be augmented with optional settings: 'baseUrl', 'paths' and 'rootDirs' - they are used to
 * mitigate differences between design time structure of the project and its runtime counterpart so the same import name
 * can be resolved successfully by TypeScript compiler and runtime module loader.
 * If these settings are set then loading procedure will try to use them to resolve module name and it can of failure it will
 * fallback to standard resolution routine.
 *
 * - baseUrl - this setting controls how non-relative module names are resolved. If this setting is specified then non-relative
 * names will be resolved relative to baseUrl: i.e. if baseUrl is '/a/b' then candidate location to resolve module name 'c/d' will
 * be '/a/b/c/d'
 * - paths - this setting can only be used when baseUrl is specified. allows to tune how non-relative module names
 * will be resolved based on the content of the module name.
 * Structure of 'paths' compiler options
 * 'paths': {
 *    pattern-1: [...substitutions],
 *    pattern-2: [...substitutions],
 *    ...
 *    pattern-n: [...substitutions]
 * }
 * Pattern here is a string that can contain zero or one '*' character. During module resolution module name will be matched against
 * all patterns in the list. Matching for patterns that don't contain '*' means that module name must be equal to pattern respecting the case.
 * If pattern contains '*' then to match pattern "<prefix>*<suffix>" module name must start with the <prefix> and end with <suffix>.
 * <MatchedStar> denotes part of the module name between <prefix> and <suffix>.
 * If module name can be matches with multiple patterns then pattern with the longest prefix will be picked.
 * After selecting pattern we'll use list of substitutions to get candidate locations of the module and the try to load module
 * from the candidate location.
 * Substitution is a string that can contain zero or one '*'. To get candidate location from substitution we'll pick every
 * substitution in the list and replace '*' with <MatchedStar> string. If candidate location is not rooted it
 * will be converted to absolute using baseUrl.
 * For example:
 * baseUrl: /a/b/c
 * "paths": {
 *     // match all module names
 *     "*": [
 *         "*",        // use matched name as is,
 *                     // <matched name> will be looked as /a/b/c/<matched name>
 *
 *         "folder1/*" // substitution will convert matched name to 'folder1/<matched name>',
 *                     // since it is not rooted then final candidate location will be /a/b/c/folder1/<matched name>
 *     ],
 *     // match module names that start with 'components/'
 *     "components/*": [ "/root/components/*" ] // substitution will convert /components/folder1/<matched name> to '/root/components/folder1/<matched name>',
 *                                              // it is rooted so it will be final candidate location
 * }
 *
 * 'rootDirs' allows the project to be spreaded across multiple locations and resolve modules with relative names as if
 * they were in the same location. For example lets say there are two files
 * '/local/src/content/file1.ts'
 * '/shared/components/contracts/src/content/protocols/file2.ts'
 * After bundling content of '/shared/components/contracts/src' will be merged with '/local/src' so
 * if file1 has the following import 'import {x} from "./protocols/file2"' it will be resolved successfully in runtime.
 * 'rootDirs' provides the way to tell compiler that in order to get the whole project it should behave as if content of all
 * root dirs were merged together.
 * I.e. for the example above 'rootDirs' will have two entries: [ '/local/src', '/shared/components/contracts/src' ].
 * Compiler will first convert './protocols/file2' into absolute path relative to the location of containing file:
 * '/local/src/content/protocols/file2' and try to load it - failure.
 * Then it will search 'rootDirs' looking for a longest matching prefix of this absolute path and if such prefix is found - absolute path will
 * be converted to a path relative to found rootDir entry './content/protocols/file2' (*). As a last step compiler will check all remaining
 * entries in 'rootDirs', use them to build absolute path out of (*) and try to resolve module from this location.
 */
function tryLoadModuleUsingOptionalResolutionSettings(extensions: Extensions, moduleName: string, containingDirectory: string, loader: ResolutionKindSpecificLoader,
    state: ModuleResolutionState): Resolved | undefined {

    const resolved = tryLoadModuleUsingPathsIfEligible(extensions, moduleName, loader, state);
    if (resolved) return resolved.value;

    if (!isExternalModuleNameRelative(moduleName)) {
        return tryLoadModuleUsingBaseUrl(extensions, moduleName, loader, state);
    }
    else {
        return tryLoadModuleUsingRootDirs(extensions, moduleName, containingDirectory, loader, state);
    }
}

function tryLoadModuleUsingPathsIfEligible(extensions: Extensions, moduleName: string, loader: ResolutionKindSpecificLoader, state: ModuleResolutionState) {
    const { baseUrl, paths, configFile } = state.compilerOptions;
    if (paths && !pathIsRelative(moduleName)) {
        if (state.traceEnabled) {
            if (baseUrl) {
                trace(state.host, Diagnostics.baseUrl_option_is_set_to_0_using_this_value_to_resolve_non_relative_module_name_1, baseUrl, moduleName);
            }
            trace(state.host, Diagnostics.paths_option_is_specified_looking_for_a_pattern_to_match_module_name_0, moduleName);
        }
        const baseDirectory = getPathsBasePath(state.compilerOptions, state.host)!; // Always defined when 'paths' is defined
        const pathPatterns = configFile?.configFileSpecs ? configFile.configFileSpecs.pathPatterns ||= tryParsePatterns(paths) : undefined;
        return tryLoadModuleUsingPaths(extensions, moduleName, baseDirectory, paths, pathPatterns, loader, /*onlyRecordFailures*/ false, state);
    }
}

function tryLoadModuleUsingRootDirs(extensions: Extensions, moduleName: string, containingDirectory: string, loader: ResolutionKindSpecificLoader,
    state: ModuleResolutionState): Resolved | undefined {

    if (!state.compilerOptions.rootDirs) {
        return undefined;
    }

    if (state.traceEnabled) {
        trace(state.host, Diagnostics.rootDirs_option_is_set_using_it_to_resolve_relative_module_name_0, moduleName);
    }

    const candidate = normalizePath(combinePaths(containingDirectory, moduleName));

    let matchedRootDir: string | undefined;
    let matchedNormalizedPrefix: string | undefined;
    for (const rootDir of state.compilerOptions.rootDirs) {
        // rootDirs are expected to be absolute
        // in case of tsconfig.json this will happen automatically - compiler will expand relative names
        // using location of tsconfig.json as base location
        let normalizedRoot = normalizePath(rootDir);
        if (!endsWith(normalizedRoot, directorySeparator)) {
            normalizedRoot += directorySeparator;
        }
        const isLongestMatchingPrefix =
            startsWith(candidate, normalizedRoot) &&
            (matchedNormalizedPrefix === undefined || matchedNormalizedPrefix.length < normalizedRoot.length);

        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Checking_if_0_is_the_longest_matching_prefix_for_1_2, normalizedRoot, candidate, isLongestMatchingPrefix);
        }

        if (isLongestMatchingPrefix) {
            matchedNormalizedPrefix = normalizedRoot;
            matchedRootDir = rootDir;
        }
    }
    if (matchedNormalizedPrefix) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Longest_matching_prefix_for_0_is_1, candidate, matchedNormalizedPrefix);
        }
        const suffix = candidate.substr(matchedNormalizedPrefix.length);

        // first - try to load from a initial location
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Loading_0_from_the_root_dir_1_candidate_location_2, suffix, matchedNormalizedPrefix, candidate);
        }
        const resolvedFileName = loader(extensions, candidate, !directoryProbablyExists(containingDirectory, state.host), state);
        if (resolvedFileName) {
            return resolvedFileName;
        }

        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Trying_other_entries_in_rootDirs);
        }
        // then try to resolve using remaining entries in rootDirs
        for (const rootDir of state.compilerOptions.rootDirs) {
            if (rootDir === matchedRootDir) {
                // skip the initially matched entry
                continue;
            }
            const candidate = combinePaths(normalizePath(rootDir), suffix);
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.Loading_0_from_the_root_dir_1_candidate_location_2, suffix, rootDir, candidate);
            }
            const baseDirectory = getDirectoryPath(candidate);
            const resolvedFileName = loader(extensions, candidate, !directoryProbablyExists(baseDirectory, state.host), state);
            if (resolvedFileName) {
                return resolvedFileName;
            }
        }
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Module_resolution_using_rootDirs_has_failed);
        }
    }
    return undefined;
}

function tryLoadModuleUsingBaseUrl(extensions: Extensions, moduleName: string, loader: ResolutionKindSpecificLoader, state: ModuleResolutionState): Resolved | undefined {
    const { baseUrl } = state.compilerOptions;
    if (!baseUrl) {
        return undefined;
    }
    if (state.traceEnabled) {
        trace(state.host, Diagnostics.baseUrl_option_is_set_to_0_using_this_value_to_resolve_non_relative_module_name_1, baseUrl, moduleName);
    }
    const candidate = normalizePath(combinePaths(baseUrl, moduleName));
    if (state.traceEnabled) {
        trace(state.host, Diagnostics.Resolving_module_name_0_relative_to_base_url_1_2, moduleName, baseUrl, candidate);
    }
    return loader(extensions, candidate, !directoryProbablyExists(getDirectoryPath(candidate), state.host), state);
}

/**
 * Expose resolution logic to allow us to use Node module resolution logic from arbitrary locations.
 * No way to do this with `require()`: https://github.com/nodejs/node/issues/5963
 * Throws an error if the module can't be resolved.
 *
 * @internal
 */
export function resolveJSModule(moduleName: string, initialDir: string, host: ModuleResolutionHost): string {
    const { resolvedModule, failedLookupLocations } = tryResolveJSModuleWorker(moduleName, initialDir, host);
    if (!resolvedModule) {
        throw new Error(`Could not resolve JS module '${moduleName}' starting at '${initialDir}'. Looked in: ${failedLookupLocations?.join(", ")}`);
    }
    return resolvedModule.resolvedFileName;
}

/** @internal */
export enum NodeResolutionFeatures {
    None = 0,
    // resolving `#local` names in your own package.json
    Imports = 1 << 1,
    // resolving `your-own-name` from your own package.json
    SelfName = 1 << 2,
    // respecting the `.exports` member of packages' package.json files and its (conditional) mappings of export names
    Exports = 1 << 3,
    // allowing `*` in the LHS of an export to be followed by more content, eg `"./whatever/*.js"`
    // not supported in node 12 - https://github.com/nodejs/Release/issues/690
    ExportsPatternTrailers = 1 << 4,
    AllFeatures = Imports | SelfName | Exports | ExportsPatternTrailers,

    Node16Default = Imports | SelfName | Exports | ExportsPatternTrailers,

    NodeNextDefault = AllFeatures,

    BundlerDefault = Imports | SelfName | Exports | ExportsPatternTrailers,

    EsmMode = 1 << 5,
}

function node16ModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions,
        host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference,
        resolutionMode?: ResolutionMode): ResolvedModuleWithFailedLookupLocations {
    return nodeNextModuleNameResolverWorker(
        NodeResolutionFeatures.Node16Default,
        moduleName,
        containingFile,
        compilerOptions,
        host,
        cache,
        redirectedReference,
        resolutionMode
    );
}

function nodeNextModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions,
        host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference,
        resolutionMode?: ResolutionMode): ResolvedModuleWithFailedLookupLocations {
    return nodeNextModuleNameResolverWorker(
        NodeResolutionFeatures.NodeNextDefault,
        moduleName,
        containingFile,
        compilerOptions,
        host,
        cache,
        redirectedReference,
        resolutionMode
    );
}

function nodeNextModuleNameResolverWorker(features: NodeResolutionFeatures, moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference, resolutionMode?: ResolutionMode): ResolvedModuleWithFailedLookupLocations {
    const containingDirectory = getDirectoryPath(containingFile);

    // es module file or cjs-like input file, use a variant of the legacy cjs resolver that supports the selected modern features
    const esmMode = resolutionMode === ModuleKind.ESNext ? NodeResolutionFeatures.EsmMode : 0;
    let extensions = compilerOptions.noDtsResolution ? Extensions.ImplementationFiles : Extensions.TypeScript | Extensions.JavaScript | Extensions.Declaration;
    if (getResolveJsonModule(compilerOptions)) {
        extensions |= Extensions.Json;
    }
    return nodeModuleNameResolverWorker(features | esmMode, moduleName, containingDirectory, compilerOptions, host, cache, extensions, /*isConfigLookup*/ false, redirectedReference);
}

function tryResolveJSModuleWorker(moduleName: string, initialDir: string, host: ModuleResolutionHost): ResolvedModuleWithFailedLookupLocations {
    return nodeModuleNameResolverWorker(
        NodeResolutionFeatures.None,
        moduleName,
        initialDir,
        { moduleResolution: ModuleResolutionKind.Node10, allowJs: true },
        host,
        /*cache*/ undefined,
        Extensions.JavaScript,
        /*isConfigLookup*/ false,
        /*redirectedReference*/ undefined);
}

export function bundlerModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference): ResolvedModuleWithFailedLookupLocations {
    const containingDirectory = getDirectoryPath(containingFile);
    let extensions = compilerOptions.noDtsResolution ? Extensions.ImplementationFiles : Extensions.TypeScript | Extensions.JavaScript | Extensions.Declaration;
    if (getResolveJsonModule(compilerOptions)) {
        extensions |= Extensions.Json;
    }
    return nodeModuleNameResolverWorker(getNodeResolutionFeatures(compilerOptions), moduleName, containingDirectory, compilerOptions, host, cache, extensions, /*isConfigLookup*/ false, redirectedReference);
}

export function nodeModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference): ResolvedModuleWithFailedLookupLocations;
/** @internal */ export function nodeModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference, lookupConfig?: boolean): ResolvedModuleWithFailedLookupLocations; // eslint-disable-line @typescript-eslint/unified-signatures
export function nodeModuleNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: ModuleResolutionCache, redirectedReference?: ResolvedProjectReference, isConfigLookup?: boolean): ResolvedModuleWithFailedLookupLocations {
    let extensions;
    if (isConfigLookup) {
        extensions = Extensions.Json;
    }
    else if (compilerOptions.noDtsResolution) {
        extensions = Extensions.ImplementationFiles;
        if (getResolveJsonModule(compilerOptions)) extensions |= Extensions.Json;
    }
    else {
        extensions = getResolveJsonModule(compilerOptions)
            ? Extensions.TypeScript | Extensions.JavaScript | Extensions.Declaration | Extensions.Json
            : Extensions.TypeScript | Extensions.JavaScript | Extensions.Declaration;
    }
    return nodeModuleNameResolverWorker(NodeResolutionFeatures.None, moduleName, getDirectoryPath(containingFile), compilerOptions, host, cache, extensions, !!isConfigLookup, redirectedReference);
}

/** @internal */
export function nodeNextJsonConfigResolver(moduleName: string, containingFile: string, host: ModuleResolutionHost): ResolvedModuleWithFailedLookupLocations {
    return nodeModuleNameResolverWorker(NodeResolutionFeatures.NodeNextDefault, moduleName, getDirectoryPath(containingFile), { moduleResolution: ModuleResolutionKind.NodeNext }, host, /*cache*/ undefined, Extensions.Json, /*isConfigLookup*/ true, /*redirectedReference*/ undefined);
}

function nodeModuleNameResolverWorker(features: NodeResolutionFeatures, moduleName: string, containingDirectory: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache: ModuleResolutionCache | undefined, extensions: Extensions, isConfigLookup: boolean, redirectedReference: ResolvedProjectReference | undefined): ResolvedModuleWithFailedLookupLocations {
    const traceEnabled = isTraceEnabled(compilerOptions, host);

    const failedLookupLocations: string[] = [];
    const affectingLocations: string[] = [];
    const conditions = getConditions(compilerOptions, !!(features & NodeResolutionFeatures.EsmMode));

    const diagnostics: Diagnostic[] = [];
    const state: ModuleResolutionState = {
        compilerOptions,
        host,
        traceEnabled,
        failedLookupLocations,
        affectingLocations,
        packageJsonInfoCache: cache,
        features,
        conditions,
        requestContainingDirectory: containingDirectory,
        reportDiagnostic: diag => void diagnostics.push(diag),
        isConfigLookup,
        candidateIsFromPackageJsonField: false,
    };

    if (traceEnabled && moduleResolutionSupportsPackageJsonExportsAndImports(getEmitModuleResolutionKind(compilerOptions))) {
        trace(host, Diagnostics.Resolving_in_0_mode_with_conditions_1, features & NodeResolutionFeatures.EsmMode ? "ESM" : "CJS", conditions.map(c => `'${c}'`).join(", "));
    }

    let result;
    if (getEmitModuleResolutionKind(compilerOptions) === ModuleResolutionKind.Node10) {
        const priorityExtensions = extensions & (Extensions.TypeScript | Extensions.Declaration);
        const secondaryExtensions = extensions & ~(Extensions.TypeScript | Extensions.Declaration);
        result =
            priorityExtensions && tryResolve(priorityExtensions, state) ||
            secondaryExtensions && tryResolve(secondaryExtensions, state) ||
            undefined;
    }
    else {
        result = tryResolve(extensions, state);
    }

    // For non-relative names that resolved to JS but no types in modes that look up an "import" condition in package.json "exports",
    // try again with "exports" disabled to try to detect if this is likely a configuration error in a dependency's package.json.
    let legacyResult;
    if (result?.value?.isExternalLibraryImport
        && !isConfigLookup
        && extensions & (Extensions.TypeScript | Extensions.Declaration)
        && features & NodeResolutionFeatures.Exports
        && !isExternalModuleNameRelative(moduleName)
        && !extensionIsOk(Extensions.TypeScript | Extensions.Declaration, result.value.resolved.extension)
        && conditions.indexOf("import") > -1
    ) {
        traceIfEnabled(state, Diagnostics.Resolution_of_non_relative_name_failed_trying_with_modern_Node_resolution_features_disabled_to_see_if_npm_library_needs_configuration_update);
        const diagnosticState = {
            ...state,
            features: state.features & ~NodeResolutionFeatures.Exports,
            reportDiagnostic: noop,
        };
        const diagnosticResult = tryResolve(extensions & (Extensions.TypeScript | Extensions.Declaration), diagnosticState);
        if (diagnosticResult?.value?.isExternalLibraryImport) {
            legacyResult = diagnosticResult.value.resolved.path;
        }
    }

    return createResolvedModuleWithFailedLookupLocationsHandlingSymlink(
        moduleName,
        result?.value?.resolved,
        result?.value?.isExternalLibraryImport,
        failedLookupLocations,
        affectingLocations,
        diagnostics,
        state,
        legacyResult,
    );

    function tryResolve(extensions: Extensions, state: ModuleResolutionState): SearchResult<{ resolved: Resolved, isExternalLibraryImport: boolean }> {
        const loader: ResolutionKindSpecificLoader = (extensions, candidate, onlyRecordFailures, state) => nodeLoadModuleByRelativeName(extensions, candidate, onlyRecordFailures, state, /*considerPackageJson*/ true);
        const resolved = tryLoadModuleUsingOptionalResolutionSettings(extensions, moduleName, containingDirectory, loader, state);
        if (resolved) {
            return toSearchResult({ resolved, isExternalLibraryImport: pathContainsNodeModules(resolved.path) });
        }

        if (!isExternalModuleNameRelative(moduleName)) {
            let resolved: SearchResult<Resolved> | undefined;
            if (features & NodeResolutionFeatures.Imports && startsWith(moduleName, "#")) {
                resolved = loadModuleFromImports(extensions, moduleName, containingDirectory, state, cache, redirectedReference);
            }
            if (!resolved && features & NodeResolutionFeatures.SelfName) {
                resolved = loadModuleFromSelfNameReference(extensions, moduleName, containingDirectory, state, cache, redirectedReference);
            }
            if (!resolved) {
                if (moduleName.indexOf(":") > -1) {
                    if (traceEnabled) {
                        trace(host, Diagnostics.Skipping_module_0_that_looks_like_an_absolute_URI_target_file_types_Colon_1, moduleName, formatExtensions(extensions));
                    }
                    return undefined;
                }
                if (traceEnabled) {
                    trace(host, Diagnostics.Loading_module_0_from_node_modules_folder_target_file_types_Colon_1, moduleName, formatExtensions(extensions));
                }
                resolved = loadModuleFromNearestNodeModulesDirectory(extensions, moduleName, containingDirectory, state, cache, redirectedReference);
            }
            if (extensions & Extensions.Declaration) {
                resolved ??= resolveFromTypeRoot(moduleName, state);
            }
            // For node_modules lookups, get the real path so that multiple accesses to an `npm link`-ed module do not create duplicate files.
            return resolved && { value: resolved.value && { resolved: resolved.value, isExternalLibraryImport: true } };
        }
        else {
            const { path: candidate, parts } = normalizePathForCJSResolution(containingDirectory, moduleName);
            const resolved = nodeLoadModuleByRelativeName(extensions, candidate, /*onlyRecordFailures*/ false, state, /*considerPackageJson*/ true);
            // Treat explicit "node_modules" import as an external library import.
            return resolved && toSearchResult({ resolved, isExternalLibraryImport: contains(parts, "node_modules") });
        }
    }

}

// If you import from "." inside a containing directory "/foo", the result of `normalizePath`
// would be "/foo", but this loses the information that `foo` is a directory and we intended
// to look inside of it. The Node CommonJS resolution algorithm doesn't call this out
// (https://nodejs.org/api/modules.html#all-together), but it seems that module paths ending
// in `.` are actually normalized to `./` before proceeding with the resolution algorithm.
function normalizePathForCJSResolution(containingDirectory: string, moduleName: string) {
    const combined = combinePaths(containingDirectory, moduleName);
    const parts = getPathComponents(combined);
    const lastPart = lastOrUndefined(parts);
    const path = lastPart === "." || lastPart === ".." ? ensureTrailingDirectorySeparator(normalizePath(combined)) : normalizePath(combined);
    return { path, parts };
}

function realPath(path: string, host: ModuleResolutionHost, traceEnabled: boolean): string {
    if (!host.realpath) {
        return path;
    }

    const real = normalizePath(host.realpath(path));
    if (traceEnabled) {
        trace(host, Diagnostics.Resolving_real_path_for_0_result_1, path, real);
    }
    Debug.assert(host.fileExists(real), `${path} linked to nonexistent file ${real}`);
    return real;
}

function nodeLoadModuleByRelativeName(extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState, considerPackageJson: boolean): Resolved | undefined {
    if (state.traceEnabled) {
        trace(state.host, Diagnostics.Loading_module_as_file_Slash_folder_candidate_module_location_0_target_file_types_Colon_1, candidate, formatExtensions(extensions));
    }
    if (!hasTrailingDirectorySeparator(candidate)) {
        if (!onlyRecordFailures) {
            const parentOfCandidate = getDirectoryPath(candidate);
            if (!directoryProbablyExists(parentOfCandidate, state.host)) {
                if (state.traceEnabled) {
                    trace(state.host, Diagnostics.Directory_0_does_not_exist_skipping_all_lookups_in_it, parentOfCandidate);
                }
                onlyRecordFailures = true;
            }
        }
        const resolvedFromFile = loadModuleFromFile(extensions, candidate, onlyRecordFailures, state);
        if (resolvedFromFile) {
            const packageDirectory = considerPackageJson ? parseNodeModuleFromPath(resolvedFromFile.path) : undefined;
            const packageInfo = packageDirectory ? getPackageJsonInfo(packageDirectory, /*onlyRecordFailures*/ false, state) : undefined;
            return withPackageId(packageInfo, resolvedFromFile);
        }
    }
    if (!onlyRecordFailures) {
        const candidateExists = directoryProbablyExists(candidate, state.host);
        if (!candidateExists) {
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.Directory_0_does_not_exist_skipping_all_lookups_in_it, candidate);
            }
            onlyRecordFailures = true;
        }
    }
    // esm mode relative imports shouldn't do any directory lookups (either inside `package.json`
    // files or implicit `index.js`es). This is a notable departure from cjs norms, where `./foo/pkg`
    // could have been redirected by `./foo/pkg/package.json` to an arbitrary location!
    if (!(state.features & NodeResolutionFeatures.EsmMode)) {
        return loadNodeModuleFromDirectory(extensions, candidate, onlyRecordFailures, state, considerPackageJson);
    }
    return undefined;
}

/** @internal */
export const nodeModulesPathPart = "/node_modules/";
/** @internal */
export function pathContainsNodeModules(path: string): boolean {
    return stringContains(path, nodeModulesPathPart);
}

/**
 * This will be called on the successfully resolved path from `loadModuleFromFile`.
 * (Not needed for `loadModuleFromNodeModules` as that looks up the `package.json` as part of resolution.)
 *
 * packageDirectory is the directory of the package itself.
 *   For `blah/node_modules/foo/index.d.ts` this is packageDirectory: "foo"
 *   For `/node_modules/foo/bar.d.ts` this is packageDirectory: "foo"
 *   For `/node_modules/@types/foo/bar/index.d.ts` this is packageDirectory: "@types/foo"
 *   For `/node_modules/foo/bar/index.d.ts` this is packageDirectory: "foo"
 *
 * @internal
 */
export function parseNodeModuleFromPath(resolved: string, isFolder?: boolean): string | undefined {
    const path = normalizePath(resolved);
    const idx = path.lastIndexOf(nodeModulesPathPart);
    if (idx === -1) {
        return undefined;
    }

    const indexAfterNodeModules = idx + nodeModulesPathPart.length;
    let indexAfterPackageName = moveToNextDirectorySeparatorIfAvailable(path, indexAfterNodeModules, isFolder);
    if (path.charCodeAt(indexAfterNodeModules) === CharacterCodes.at) {
        indexAfterPackageName = moveToNextDirectorySeparatorIfAvailable(path, indexAfterPackageName, isFolder);
    }
    return path.slice(0, indexAfterPackageName);
}

function moveToNextDirectorySeparatorIfAvailable(path: string, prevSeparatorIndex: number, isFolder: boolean | undefined): number {
    const nextSeparatorIndex = path.indexOf(directorySeparator, prevSeparatorIndex + 1);
    return nextSeparatorIndex === -1 ? isFolder ? path.length : prevSeparatorIndex : nextSeparatorIndex;
}

function loadModuleFromFileNoPackageId(extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState): Resolved | undefined {
    return noPackageId(loadModuleFromFile(extensions, candidate, onlyRecordFailures, state));
}

/**
 * @param {boolean} onlyRecordFailures - if true then function won't try to actually load files but instead record all attempts as failures. This flag is necessary
 * in cases when we know upfront that all load attempts will fail (because containing folder does not exists) however we still need to record all failed lookup locations.
 */
function loadModuleFromFile(extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState): PathAndExtension | undefined {
    // ./foo.js -> ./foo.ts
    const resolvedByReplacingExtension = loadModuleFromFileNoImplicitExtensions(extensions, candidate, onlyRecordFailures, state);
    if (resolvedByReplacingExtension) {
        return resolvedByReplacingExtension;
    }

    // ./foo -> ./foo.ts
    if (!(state.features & NodeResolutionFeatures.EsmMode)) {
        // First, try adding an extension. An import of "foo" could be matched by a file "foo.ts", or "foo.js" by "foo.js.ts"
        const resolvedByAddingExtension = tryAddingExtensions(candidate, extensions, "", onlyRecordFailures, state);
        if (resolvedByAddingExtension) {
            return resolvedByAddingExtension;
        }
    }
}

function loadModuleFromFileNoImplicitExtensions(extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState): PathAndExtension | undefined {
    const filename = getBaseFileName(candidate);
    if (filename.indexOf(".") === -1) {
        return undefined; // extensionless import, no lookups performed, since we don't support extensionless files
    }
    let extensionless = removeFileExtension(candidate);
    if (extensionless === candidate) {
        // Once TS native extensions are handled, handle arbitrary extensions for declaration file mapping
        extensionless = candidate.substring(0, candidate.lastIndexOf("."));
    }

    const extension = candidate.substring(extensionless.length);
    if (state.traceEnabled) {
        trace(state.host, Diagnostics.File_name_0_has_a_1_extension_stripping_it, candidate, extension);
    }
    return tryAddingExtensions(extensionless, extensions, extension, onlyRecordFailures, state);
}

/**
 * This function is only ever called with paths written in package.json files - never
 * module specifiers written in source files - and so it always allows the

 * candidate to end with a TS extension (but will also try substituting a JS extension for a TS extension).
 */
function loadFileNameFromPackageJsonField(extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState): PathAndExtension | undefined {
    if (extensions & Extensions.TypeScript && fileExtensionIsOneOf(candidate, supportedTSImplementationExtensions) ||
        extensions & Extensions.Declaration && fileExtensionIsOneOf(candidate, supportedDeclarationExtensions)
    ) {
        const result = tryFile(candidate, onlyRecordFailures, state);
        return result !== undefined ? { path: candidate, ext: tryExtractTSExtension(candidate) as Extension, resolvedUsingTsExtension: undefined } : undefined;
    }

    if (state.isConfigLookup && extensions === Extensions.Json && fileExtensionIs(candidate, Extension.Json)) {
        const result = tryFile(candidate, onlyRecordFailures, state);
        return result !== undefined ? { path: candidate, ext: Extension.Json, resolvedUsingTsExtension: undefined } : undefined;
    }

    return loadModuleFromFileNoImplicitExtensions(extensions, candidate, onlyRecordFailures, state);
}

/** Try to return an existing file that adds one of the `extensions` to `candidate`. */
function tryAddingExtensions(candidate: string, extensions: Extensions, originalExtension: string, onlyRecordFailures: boolean, state: ModuleResolutionState): PathAndExtension | undefined {
    if (!onlyRecordFailures) {
        // check if containing folder exists - if it doesn't then just record failures for all supported extensions without disk probing
        const directory = getDirectoryPath(candidate);
        if (directory) {
            onlyRecordFailures = !directoryProbablyExists(directory, state.host);
        }
    }

    switch (originalExtension) {
        case Extension.Mjs:
        case Extension.Mts:
        case Extension.Dmts:
            return extensions & Extensions.TypeScript && tryExtension(Extension.Mts, originalExtension === Extension.Mts || originalExtension === Extension.Dmts)
                || extensions & Extensions.Declaration && tryExtension(Extension.Dmts, originalExtension === Extension.Mts || originalExtension === Extension.Dmts)
                || extensions & Extensions.JavaScript && tryExtension(Extension.Mjs)
                || undefined;
        case Extension.Cjs:
        case Extension.Cts:
        case Extension.Dcts:
            return extensions & Extensions.TypeScript && tryExtension(Extension.Cts, originalExtension === Extension.Cts || originalExtension === Extension.Dcts)
                || extensions & Extensions.Declaration && tryExtension(Extension.Dcts, originalExtension === Extension.Cts || originalExtension === Extension.Dcts)
                || extensions & Extensions.JavaScript && tryExtension(Extension.Cjs)
                || undefined;
        case Extension.Json:
            return extensions & Extensions.Declaration && tryExtension(".d.json.ts")
                || extensions & Extensions.Json && tryExtension(Extension.Json)
                || undefined;
        case Extension.Tsx:
        case Extension.Jsx:
            // basically idendical to the ts/js case below, but prefers matching tsx and jsx files exactly before falling back to the ts or js file path
            // (historically, we disallow having both a a.ts and a.tsx file in the same compilation, since their outputs clash)
            // TODO: We should probably error if `"./a.tsx"` resolved to `"./a.ts"`, right?
            return extensions & Extensions.TypeScript && (tryExtension(Extension.Tsx, originalExtension === Extension.Tsx) || tryExtension(Extension.Ts, originalExtension === Extension.Tsx))
                || extensions & Extensions.Declaration && tryExtension(Extension.Dts, originalExtension === Extension.Tsx)
                || extensions & Extensions.JavaScript && (tryExtension(Extension.Jsx) || tryExtension(Extension.Js))
                || undefined;
        case Extension.Ts:
        case Extension.Dts:
        case Extension.Js:
        case "":
            return extensions & Extensions.TypeScript && (tryExtension(Extension.Ts, originalExtension === Extension.Ts || originalExtension === Extension.Dts) || tryExtension(Extension.Tsx, originalExtension === Extension.Ts || originalExtension === Extension.Dts))
                || extensions & Extensions.Declaration && tryExtension(Extension.Dts, originalExtension === Extension.Ts || originalExtension === Extension.Dts)
                || extensions & Extensions.JavaScript && (tryExtension(Extension.Js) || tryExtension(Extension.Jsx))
                || state.isConfigLookup && tryExtension(Extension.Json)
                || undefined;
        default:
            return extensions & Extensions.Declaration && !isDeclarationFileName(candidate + originalExtension) && tryExtension(`.d${originalExtension}.ts`)
                || undefined;

    }

    function tryExtension(ext: string, resolvedUsingTsExtension?: boolean): PathAndExtension | undefined {
        const path = tryFile(candidate + ext, onlyRecordFailures, state);
        return path === undefined ? undefined : { path, ext, resolvedUsingTsExtension: !state.candidateIsFromPackageJsonField && resolvedUsingTsExtension };
    }
}

/** Return the file if it exists. */
function tryFile(fileName: string, onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
    if (!state.compilerOptions.moduleSuffixes?.length) {
        return tryFileLookup(fileName, onlyRecordFailures, state);
    }

    const ext = tryGetExtensionFromPath(fileName) ?? "";
    const fileNameNoExtension = ext ? removeExtension(fileName, ext) : fileName;
    return forEach(state.compilerOptions.moduleSuffixes, suffix => tryFileLookup(fileNameNoExtension + suffix + ext, onlyRecordFailures, state));
}

function tryFileLookup(fileName: string, onlyRecordFailures: boolean, state: ModuleResolutionState): string | undefined {
    if (!onlyRecordFailures) {
        if (state.host.fileExists(fileName)) {
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.File_0_exists_use_it_as_a_name_resolution_result, fileName);
            }
            return fileName;
        }
        else {
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.File_0_does_not_exist, fileName);
            }
        }
    }
    state.failedLookupLocations?.push(fileName);
    return undefined;
}

function loadNodeModuleFromDirectory(extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState, considerPackageJson = true) {
    const packageInfo = considerPackageJson ? getPackageJsonInfo(candidate, onlyRecordFailures, state) : undefined;
    const packageJsonContent = packageInfo && packageInfo.contents.packageJsonContent;
    const versionPaths = packageInfo && getVersionPathsOfPackageJsonInfo(packageInfo, state);
    return withPackageId(packageInfo, loadNodeModuleFromDirectoryWorker(extensions, candidate, onlyRecordFailures, state, packageJsonContent, versionPaths));
}

/** @internal */
export interface GetPackageJsonEntrypointsHost extends ModuleResolutionHost {
    readDirectory: CompilerHost["readDirectory"];
}

/** @internal */
export function getEntrypointsFromPackageJsonInfo(
    packageJsonInfo: PackageJsonInfo,
    options: CompilerOptions,
    host: GetPackageJsonEntrypointsHost,
    cache: ModuleResolutionCache | undefined,
    resolveJs?: boolean,
): string[] | false {
    if (!resolveJs && packageJsonInfo.contents.resolvedEntrypoints !== undefined) {
        // Cached value excludes resolutions to JS files - those could be
        // cached separately, but they're used rarely.
        return packageJsonInfo.contents.resolvedEntrypoints;
    }

    let entrypoints: string[] | undefined;
    const extensions = Extensions.TypeScript | Extensions.Declaration | (resolveJs ? Extensions.JavaScript : 0);
    const features = getNodeResolutionFeatures(options);
    const loadPackageJsonMainState = getTemporaryModuleResolutionState(cache?.getPackageJsonInfoCache(), host, options);
    loadPackageJsonMainState.conditions = getConditions(options);
    loadPackageJsonMainState.requestContainingDirectory = packageJsonInfo.packageDirectory;
    const mainResolution = loadNodeModuleFromDirectoryWorker(
        extensions,
        packageJsonInfo.packageDirectory,
        /*onlyRecordFailures*/ false,
        loadPackageJsonMainState,
        packageJsonInfo.contents.packageJsonContent,
        getVersionPathsOfPackageJsonInfo(packageJsonInfo, loadPackageJsonMainState));
    entrypoints = append(entrypoints, mainResolution?.path);

    if (features & NodeResolutionFeatures.Exports && packageJsonInfo.contents.packageJsonContent.exports) {
        const conditionSets = deduplicate(
            [getConditions(options, /*esmMode*/ true), getConditions(options, /*esmMode*/ false)],
            arrayIsEqualTo
        );
        for (const conditions of conditionSets) {
            const loadPackageJsonExportsState = { ...loadPackageJsonMainState, failedLookupLocations: [], conditions, host };
            const exportResolutions = loadEntrypointsFromExportMap(
                packageJsonInfo,
                packageJsonInfo.contents.packageJsonContent.exports,
                loadPackageJsonExportsState,
                extensions);
            if (exportResolutions) {
                for (const resolution of exportResolutions) {
                    entrypoints = appendIfUnique(entrypoints, resolution.path);
                }
            }
        }
    }

    return packageJsonInfo.contents.resolvedEntrypoints = entrypoints || false;
}

function loadEntrypointsFromExportMap(
    scope: PackageJsonInfo,
    exports: object,
    state: ModuleResolutionState & { host: GetPackageJsonEntrypointsHost },
    extensions: Extensions,
): PathAndExtension[] | undefined {
    let entrypoints: PathAndExtension[] | undefined;
    if (isArray(exports)) {
        for (const target of exports) {
            loadEntrypointsFromTargetExports(target);
        }
    }
    // eslint-disable-next-line no-null/no-null
    else if (typeof exports === "object" && exports !== null && allKeysStartWithDot(exports as MapLike<unknown>)) {
        for (const key in exports) {
            loadEntrypointsFromTargetExports((exports as MapLike<unknown>)[key]);
        }
    }
    else {
        loadEntrypointsFromTargetExports(exports);
    }
    return entrypoints;

    function loadEntrypointsFromTargetExports(target: unknown): boolean | undefined {
        if (typeof target === "string" && startsWith(target, "./")) {
            if (target.indexOf("*") >= 0 && state.host.readDirectory) {
                if (target.indexOf("*") !== target.lastIndexOf("*")) {
                    return false;
                }

                state.host.readDirectory(
                    scope.packageDirectory,
                    extensionsToExtensionsArray(extensions),
                    /*excludes*/ undefined,
                    [changeAnyExtension(target.replace("*", "**/*"), getDeclarationEmitExtensionForPath(target))]
                ).forEach(entry => {
                    entrypoints = appendIfUnique(entrypoints, {
                        path: entry,
                        ext: getAnyExtensionFromPath(entry),
                        resolvedUsingTsExtension: undefined
                    });
                });
            }
            else {
                const partsAfterFirst = getPathComponents(target).slice(2);
                if (partsAfterFirst.indexOf("..") >= 0 || partsAfterFirst.indexOf(".") >= 0 || partsAfterFirst.indexOf("node_modules") >= 0) {
                    return false;
                }
                const resolvedTarget = combinePaths(scope.packageDirectory, target);
                const finalPath = getNormalizedAbsolutePath(resolvedTarget, state.host.getCurrentDirectory?.());
                const result = loadFileNameFromPackageJsonField(extensions, finalPath, /*onlyRecordFailures*/ false, state);
                if (result) {
                    entrypoints = appendIfUnique(entrypoints, result, (a, b) => a.path === b.path);
                    return true;
                }
            }
        }
        else if (Array.isArray(target)) {
            for (const t of target) {
                const success = loadEntrypointsFromTargetExports(t);
                if (success) {
                    return true;
                }
            }
        }
        // eslint-disable-next-line no-null/no-null
        else if (typeof target === "object" && target !== null) {
            return forEach(getOwnKeys(target as MapLike<unknown>), key => {
                if (key === "default" || contains(state.conditions, key) || isApplicableVersionedTypesKey(state.conditions, key)) {
                    loadEntrypointsFromTargetExports((target as MapLike<unknown>)[key]);
                    return true;
                }
            });
        }
    }
}

/** @internal */
export function getTemporaryModuleResolutionState(packageJsonInfoCache: PackageJsonInfoCache | undefined, host: ModuleResolutionHost, options: CompilerOptions): ModuleResolutionState {
    return {
        host,
        compilerOptions: options,
        traceEnabled: isTraceEnabled(options, host),
        failedLookupLocations: undefined,
        affectingLocations: undefined,
        packageJsonInfoCache,
        features: NodeResolutionFeatures.None,
        conditions: emptyArray,
        requestContainingDirectory: undefined,
        reportDiagnostic: noop,
        isConfigLookup: false,
        candidateIsFromPackageJsonField: false,
    };
}

/** @internal */
export interface PackageJsonInfo {
    packageDirectory: string;
    contents: PackageJsonInfoContents;
}
/** @internal */
export interface PackageJsonInfoContents {
    packageJsonContent: PackageJsonPathFields;
    /** false: versionPaths are not present. undefined: not yet resolved */
    versionPaths: VersionPaths | false | undefined;
    /** false: resolved to nothing. undefined: not yet resolved */
    resolvedEntrypoints: string[] | false | undefined;
}

/**
 * A function for locating the package.json scope for a given path
 *
 * @internal
 */
export function getPackageScopeForPath(fileName: string, state: ModuleResolutionState): PackageJsonInfo | undefined {
    const parts = getPathComponents(fileName);
    parts.pop();
    while (parts.length > 0) {
        const pkg = getPackageJsonInfo(getPathFromPathComponents(parts), /*onlyRecordFailures*/ false, state);
        if (pkg) {
            return pkg;
        }
        parts.pop();
    }
    return undefined;
}

function getVersionPathsOfPackageJsonInfo(packageJsonInfo: PackageJsonInfo, state: ModuleResolutionState): VersionPaths | undefined {
    if (packageJsonInfo.contents.versionPaths === undefined) {
        packageJsonInfo.contents.versionPaths = readPackageJsonTypesVersionPaths(packageJsonInfo.contents.packageJsonContent, state) || false;
    }
    return packageJsonInfo.contents.versionPaths || undefined;
}

/** @internal */
export function getPackageJsonInfo(packageDirectory: string, onlyRecordFailures: boolean, state: ModuleResolutionState): PackageJsonInfo | undefined {
    const { host, traceEnabled } = state;
    const packageJsonPath = combinePaths(packageDirectory, "package.json");
    if (onlyRecordFailures) {
        state.failedLookupLocations?.push(packageJsonPath);
        return undefined;
    }

    const existing = state.packageJsonInfoCache?.getPackageJsonInfo(packageJsonPath);
    if (existing !== undefined) {
        if (typeof existing !== "boolean") {
            if (traceEnabled) trace(host, Diagnostics.File_0_exists_according_to_earlier_cached_lookups, packageJsonPath);
            state.affectingLocations?.push(packageJsonPath);
            return existing.packageDirectory === packageDirectory ?
                existing :
                { packageDirectory, contents: existing.contents };
        }
        else {
            if (existing && traceEnabled) trace(host, Diagnostics.File_0_does_not_exist_according_to_earlier_cached_lookups, packageJsonPath);
            state.failedLookupLocations?.push(packageJsonPath);
            return undefined;
        }
    }
    const directoryExists = directoryProbablyExists(packageDirectory, host);
    if (directoryExists && host.fileExists(packageJsonPath)) {
        const packageJsonContent = readJson(packageJsonPath, host) as PackageJson;
        if (traceEnabled) {
            trace(host, Diagnostics.Found_package_json_at_0, packageJsonPath);
        }
        const result: PackageJsonInfo = { packageDirectory, contents: { packageJsonContent, versionPaths: undefined, resolvedEntrypoints: undefined } };
        state.packageJsonInfoCache?.setPackageJsonInfo(packageJsonPath, result);
        state.affectingLocations?.push(packageJsonPath);
        return result;
    }
    else {
        if (directoryExists && traceEnabled) {
            trace(host, Diagnostics.File_0_does_not_exist, packageJsonPath);
        }
        state.packageJsonInfoCache?.setPackageJsonInfo(packageJsonPath, directoryExists);
        // record package json as one of failed lookup locations - in the future if this file will appear it will invalidate resolution results
        state.failedLookupLocations?.push(packageJsonPath);
    }
}

function loadNodeModuleFromDirectoryWorker(extensions: Extensions, candidate: string, onlyRecordFailures: boolean, state: ModuleResolutionState, jsonContent: PackageJsonPathFields | undefined, versionPaths: VersionPaths | undefined): PathAndExtension | undefined {
    let packageFile: string | undefined;
    if (jsonContent) {
        if (state.isConfigLookup) {
            packageFile = readPackageJsonTSConfigField(jsonContent, candidate, state);
        }
        else {
            packageFile =
                extensions & Extensions.Declaration && readPackageJsonTypesFields(jsonContent, candidate, state) ||
                extensions & (Extensions.ImplementationFiles | Extensions.Declaration) && readPackageJsonMainField(jsonContent, candidate, state) ||
                undefined;
        }
    }

    const loader: ResolutionKindSpecificLoader = (extensions, candidate, onlyRecordFailures, state) => {
        const fromFile = tryFile(candidate, onlyRecordFailures, state);
        if (fromFile) {
            const resolved = resolvedIfExtensionMatches(extensions, fromFile);
            if (resolved) {
                return noPackageId(resolved);
            }
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.File_0_has_an_unsupported_extension_so_skipping_it, fromFile);
            }
        }

        // Even if extensions is DtsOnly, we can still look up a .ts file as a result of package.json "types"
        const expandedExtensions = extensions === Extensions.Declaration ? Extensions.TypeScript | Extensions.Declaration : extensions;
        // Don't do package.json lookup recursively, because Node.js' package lookup doesn't.

        // Disable `EsmMode` for the resolution of the package path for cjs-mode packages (so the `main` field can omit extensions)
        // (technically it only emits a deprecation warning in esm packages right now, but that's probably
        // enough to mean we don't need to support it)
        const features = state.features;
        const candidateIsFromPackageJsonField = state.candidateIsFromPackageJsonField;
        state.candidateIsFromPackageJsonField = true;
        if (jsonContent?.type !== "module") {
            state.features &= ~NodeResolutionFeatures.EsmMode;
        }
        const result = nodeLoadModuleByRelativeName(expandedExtensions, candidate, onlyRecordFailures, state, /*considerPackageJson*/ false);
        state.features = features;
        state.candidateIsFromPackageJsonField = candidateIsFromPackageJsonField;
        return result;
    };

    const onlyRecordFailuresForPackageFile = packageFile ? !directoryProbablyExists(getDirectoryPath(packageFile), state.host) : undefined;
    const onlyRecordFailuresForIndex = onlyRecordFailures || !directoryProbablyExists(candidate, state.host);
    const indexPath = combinePaths(candidate, state.isConfigLookup ? "tsconfig" : "index");

    if (versionPaths && (!packageFile || containsPath(candidate, packageFile))) {
        const moduleName = getRelativePathFromDirectory(candidate, packageFile || indexPath, /*ignoreCase*/ false);
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.package_json_has_a_typesVersions_entry_0_that_matches_compiler_version_1_looking_for_a_pattern_to_match_module_name_2, versionPaths.version, version, moduleName);
        }
        const result = tryLoadModuleUsingPaths(extensions, moduleName, candidate, versionPaths.paths, /*pathPatterns*/ undefined, loader, onlyRecordFailuresForPackageFile || onlyRecordFailuresForIndex, state);
        if (result) {
            return removeIgnoredPackageId(result.value);
        }
    }

    // It won't have a `packageId` set, because we disabled `considerPackageJson`.
    const packageFileResult = packageFile && removeIgnoredPackageId(loader(extensions, packageFile, onlyRecordFailuresForPackageFile!, state));
    if (packageFileResult) return packageFileResult;

    // esm mode resolutions don't do package `index` lookups
    if (!(state.features & NodeResolutionFeatures.EsmMode)) {
        return loadModuleFromFile(extensions, indexPath, onlyRecordFailuresForIndex, state);
    }
}

/** Resolve from an arbitrarily specified file. Return `undefined` if it has an unsupported extension. */
function resolvedIfExtensionMatches(extensions: Extensions, path: string, resolvedUsingTsExtension?: boolean): PathAndExtension | undefined {
    const ext = tryGetExtensionFromPath(path);
    return ext !== undefined && extensionIsOk(extensions, ext) ? { path, ext, resolvedUsingTsExtension } : undefined;
}

/** True if `extension` is one of the supported `extensions`. */
function extensionIsOk(extensions: Extensions, extension: string): boolean {
    return extensions & Extensions.JavaScript && (extension === Extension.Js || extension === Extension.Jsx || extension === Extension.Mjs || extension === Extension.Cjs)
        || extensions & Extensions.TypeScript && (extension === Extension.Ts || extension === Extension.Tsx || extension === Extension.Mts || extension === Extension.Cts)
        || extensions & Extensions.Declaration && (extension === Extension.Dts || extension === Extension.Dmts || extension === Extension.Dcts)
        || extensions & Extensions.Json && extension === Extension.Json
        || false;
}

/** @internal */
export function parsePackageName(moduleName: string): { packageName: string, rest: string } {
    let idx = moduleName.indexOf(directorySeparator);
    if (moduleName[0] === "@") {
        idx = moduleName.indexOf(directorySeparator, idx + 1);
    }
    return idx === -1 ? { packageName: moduleName, rest: "" } : { packageName: moduleName.slice(0, idx), rest: moduleName.slice(idx + 1) };
}

/** @internal */
export function allKeysStartWithDot(obj: MapLike<unknown>) {
    return every(getOwnKeys(obj), k => startsWith(k, "."));
}

function noKeyStartsWithDot(obj: MapLike<unknown>) {
    return !some(getOwnKeys(obj), k => startsWith(k, "."));
}

function loadModuleFromSelfNameReference(extensions: Extensions, moduleName: string, directory: string, state: ModuleResolutionState, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined): SearchResult<Resolved> {
    const directoryPath = getNormalizedAbsolutePath(combinePaths(directory, "dummy"), state.host.getCurrentDirectory?.());
    const scope = getPackageScopeForPath(directoryPath, state);
    if (!scope || !scope.contents.packageJsonContent.exports) {
        return undefined;
    }
    if (typeof scope.contents.packageJsonContent.name !== "string") {
        return undefined;
    }
    const parts = getPathComponents(moduleName); // unrooted paths should have `""` as their 0th entry
    const nameParts = getPathComponents(scope.contents.packageJsonContent.name);
    if (!every(nameParts, (p, i) => parts[i] === p)) {
        return undefined;
    }
    const trailingParts = parts.slice(nameParts.length);
    const subpath = !length(trailingParts) ? "." : `.${directorySeparator}${trailingParts.join(directorySeparator)}`;
    // Maybe TODO: splitting extensions into two priorities should be unnecessary, except
    // https://github.com/microsoft/TypeScript/issues/50762 makes the behavior different.
    // As long as that bug exists, we need to do two passes here in self-name loading
    // in order to be consistent with (non-self) library-name loading in
    // `loadModuleFromNearestNodeModulesDirectoryWorker`, which uses two passes in order
    // to prioritize `@types` packages higher up the directory tree over untyped
    // implementation packages. See the selfNameModuleAugmentation.ts test for why this
    // matters.
    //
    // However, there's an exception. If the user has `allowJs` and `declaration`, we need
    // to ensure that self-name imports of their own package can resolve back to their
    // input JS files via `tryLoadInputFileForPath` at a higher priority than their output
    // declaration files, so we need to do a single pass with all extensions for that case.
    if (getAllowJSCompilerOption(state.compilerOptions) && !pathContainsNodeModules(directory)) {
        return loadModuleFromExports(scope, extensions, subpath, state, cache, redirectedReference);
    }
    const priorityExtensions = extensions & (Extensions.TypeScript | Extensions.Declaration);
    const secondaryExtensions = extensions & ~(Extensions.TypeScript | Extensions.Declaration);
    return loadModuleFromExports(scope, priorityExtensions, subpath, state, cache, redirectedReference)
        || loadModuleFromExports(scope, secondaryExtensions, subpath, state, cache, redirectedReference);
}

function loadModuleFromExports(scope: PackageJsonInfo, extensions: Extensions, subpath: string, state: ModuleResolutionState, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined): SearchResult<Resolved> {
    if (!scope.contents.packageJsonContent.exports) {
        return undefined;
    }

    if (subpath === ".") {
        let mainExport;
        if (typeof scope.contents.packageJsonContent.exports === "string" || Array.isArray(scope.contents.packageJsonContent.exports) || (typeof scope.contents.packageJsonContent.exports === "object" && noKeyStartsWithDot(scope.contents.packageJsonContent.exports as MapLike<unknown>))) {
            mainExport = scope.contents.packageJsonContent.exports;
        }
        else if (hasProperty(scope.contents.packageJsonContent.exports as MapLike<unknown>, ".")) {
            mainExport = (scope.contents.packageJsonContent.exports as MapLike<unknown>)["."];
        }
        if (mainExport) {
            const loadModuleFromTargetImportOrExport = getLoadModuleFromTargetImportOrExport(extensions, state, cache, redirectedReference, subpath, scope, /*isImports*/ false);
            return loadModuleFromTargetImportOrExport(mainExport, "", /*pattern*/ false, ".");
        }
    }
    else if (allKeysStartWithDot(scope.contents.packageJsonContent.exports as MapLike<unknown>)) {
        if (typeof scope.contents.packageJsonContent.exports !== "object") {
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.Export_specifier_0_does_not_exist_in_package_json_scope_at_path_1, subpath, scope.packageDirectory);
            }
            return toSearchResult(/*value*/ undefined);
        }
        const result = loadModuleFromImportsOrExports(extensions, state, cache, redirectedReference, subpath, scope.contents.packageJsonContent.exports, scope, /*isImports*/ false);
        if (result) {
            return result;
        }
    }

    if (state.traceEnabled) {
        trace(state.host, Diagnostics.Export_specifier_0_does_not_exist_in_package_json_scope_at_path_1, subpath, scope.packageDirectory);
    }
    return toSearchResult(/*value*/ undefined);
}

function loadModuleFromImports(extensions: Extensions, moduleName: string, directory: string, state: ModuleResolutionState, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined): SearchResult<Resolved> {
    if (moduleName === "#" || startsWith(moduleName, "#/")) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Invalid_import_specifier_0_has_no_possible_resolutions, moduleName);
        }
        return toSearchResult(/*value*/ undefined);
    }
    const directoryPath = getNormalizedAbsolutePath(combinePaths(directory, "dummy"), state.host.getCurrentDirectory?.());
    const scope = getPackageScopeForPath(directoryPath, state);
    if (!scope) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Directory_0_has_no_containing_package_json_scope_Imports_will_not_resolve, directoryPath);
        }
        return toSearchResult(/*value*/ undefined);
    }
    if (!scope.contents.packageJsonContent.imports) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.package_json_scope_0_has_no_imports_defined, scope.packageDirectory);
        }
        return toSearchResult(/*value*/ undefined);
    }

    const result = loadModuleFromImportsOrExports(extensions, state, cache, redirectedReference, moduleName, scope.contents.packageJsonContent.imports, scope, /*isImports*/ true);
    if (result) {
        return result;
    }

    if (state.traceEnabled) {
        trace(state.host, Diagnostics.Import_specifier_0_does_not_exist_in_package_json_scope_at_path_1, moduleName, scope.packageDirectory);
    }
    return toSearchResult(/*value*/ undefined);
}

/**
 * @internal
 * From https://github.com/nodejs/node/blob/8f39f51cbbd3b2de14b9ee896e26421cc5b20121/lib/internal/modules/esm/resolve.js#L722 -
 * "longest" has some nuance as to what "longest" means in the presence of pattern trailers
 */
export function comparePatternKeys(a: string, b: string) {
    const aPatternIndex = a.indexOf("*");
    const bPatternIndex = b.indexOf("*");
    const baseLenA = aPatternIndex === -1 ? a.length : aPatternIndex + 1;
    const baseLenB = bPatternIndex === -1 ? b.length : bPatternIndex + 1;
    if (baseLenA > baseLenB) return -1;
    if (baseLenB > baseLenA) return 1;
    if (aPatternIndex === -1) return 1;
    if (bPatternIndex === -1) return -1;
    if (a.length > b.length) return -1;
    if (b.length > a.length) return 1;
    return 0;
}

function loadModuleFromImportsOrExports(extensions: Extensions, state: ModuleResolutionState, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined, moduleName: string, lookupTable: object, scope: PackageJsonInfo, isImports: boolean): SearchResult<Resolved> | undefined {
    const loadModuleFromTargetImportOrExport = getLoadModuleFromTargetImportOrExport(extensions, state, cache, redirectedReference, moduleName, scope, isImports);

    if (!endsWith(moduleName, directorySeparator) && moduleName.indexOf("*") === -1 && hasProperty(lookupTable, moduleName)) {
        const target = (lookupTable as { [idx: string]: unknown })[moduleName];
        return loadModuleFromTargetImportOrExport(target, /*subpath*/ "", /*pattern*/ false, moduleName);
    }
    const expandingKeys = sort(filter(getOwnKeys(lookupTable as MapLike<unknown>), k => k.indexOf("*") !== -1 || endsWith(k, "/")), comparePatternKeys);
    for (const potentialTarget of expandingKeys) {
        if (state.features & NodeResolutionFeatures.ExportsPatternTrailers && matchesPatternWithTrailer(potentialTarget, moduleName)) {
            const target = (lookupTable as { [idx: string]: unknown })[potentialTarget];
            const starPos = potentialTarget.indexOf("*");
            const subpath = moduleName.substring(potentialTarget.substring(0, starPos).length, moduleName.length - (potentialTarget.length - 1 - starPos));
            return loadModuleFromTargetImportOrExport(target, subpath, /*pattern*/ true, potentialTarget);
        }
        else if (endsWith(potentialTarget, "*") && startsWith(moduleName, potentialTarget.substring(0, potentialTarget.length - 1))) {
            const target = (lookupTable as { [idx: string]: unknown })[potentialTarget];
            const subpath = moduleName.substring(potentialTarget.length - 1);
            return loadModuleFromTargetImportOrExport(target, subpath, /*pattern*/ true, potentialTarget);
        }
        else if (startsWith(moduleName, potentialTarget)) {
            const target = (lookupTable as { [idx: string]: unknown })[potentialTarget];
            const subpath = moduleName.substring(potentialTarget.length);
            return loadModuleFromTargetImportOrExport(target, subpath, /*pattern*/ false, potentialTarget);
        }
    }

    function matchesPatternWithTrailer(target: string, name: string) {
        if (endsWith(target, "*")) return false; // handled by next case in loop
        const starPos = target.indexOf("*");
        if (starPos === -1) return false; // handled by last case in loop
        return startsWith(name, target.substring(0, starPos)) && endsWith(name, target.substring(starPos + 1));
    }
}

/**
 * Gets the self-recursive function specialized to retrieving the targeted import/export element for the given resolution configuration
 */
function getLoadModuleFromTargetImportOrExport(extensions: Extensions, state: ModuleResolutionState, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined, moduleName: string, scope: PackageJsonInfo, isImports: boolean) {
    return loadModuleFromTargetImportOrExport;
    function loadModuleFromTargetImportOrExport(target: unknown, subpath: string, pattern: boolean, key: string): SearchResult<Resolved> | undefined {
        if (typeof target === "string") {
            if (!pattern && subpath.length > 0 && !endsWith(target, "/")) {
                if (state.traceEnabled) {
                    trace(state.host, Diagnostics.package_json_scope_0_has_invalid_type_for_target_of_specifier_1, scope.packageDirectory, moduleName);
                }
                return toSearchResult(/*value*/ undefined);
            }
            if (!startsWith(target, "./")) {
                if (isImports && !startsWith(target, "../") && !startsWith(target, "/") && !isRootedDiskPath(target)) {
                    const combinedLookup = pattern ? target.replace(/\*/g, subpath) : target + subpath;
                    traceIfEnabled(state, Diagnostics.Using_0_subpath_1_with_target_2, "imports", key, combinedLookup);
                    traceIfEnabled(state, Diagnostics.Resolving_module_0_from_1, combinedLookup, scope.packageDirectory + "/");
                    const result = nodeModuleNameResolverWorker(state.features, combinedLookup, scope.packageDirectory + "/", state.compilerOptions, state.host, cache, extensions, /*isConfigLookup*/ false, redirectedReference);
                    return toSearchResult(result.resolvedModule ? {
                        path: result.resolvedModule.resolvedFileName,
                        extension: result.resolvedModule.extension,
                        packageId: result.resolvedModule.packageId,
                        originalPath: result.resolvedModule.originalPath,
                        resolvedUsingTsExtension: result.resolvedModule.resolvedUsingTsExtension
                    } : undefined);
                }
                if (state.traceEnabled) {
                    trace(state.host, Diagnostics.package_json_scope_0_has_invalid_type_for_target_of_specifier_1, scope.packageDirectory, moduleName);
                }
                return toSearchResult(/*value*/ undefined);
            }
            const parts = pathIsRelative(target) ? getPathComponents(target).slice(1) : getPathComponents(target);
            const partsAfterFirst = parts.slice(1);
            if (partsAfterFirst.indexOf("..") >= 0 || partsAfterFirst.indexOf(".") >= 0 || partsAfterFirst.indexOf("node_modules") >= 0) {
                if (state.traceEnabled) {
                    trace(state.host, Diagnostics.package_json_scope_0_has_invalid_type_for_target_of_specifier_1, scope.packageDirectory, moduleName);
                }
                return toSearchResult(/*value*/ undefined);
            }
            const resolvedTarget = combinePaths(scope.packageDirectory, target);
            // TODO: Assert that `resolvedTarget` is actually within the package directory? That's what the spec says.... but I'm not sure we need
            // to be in the business of validating everyone's import and export map correctness.
            const subpathParts = getPathComponents(subpath);
            if (subpathParts.indexOf("..") >= 0 || subpathParts.indexOf(".") >= 0 || subpathParts.indexOf("node_modules") >= 0) {
                if (state.traceEnabled) {
                    trace(state.host, Diagnostics.package_json_scope_0_has_invalid_type_for_target_of_specifier_1, scope.packageDirectory, moduleName);
                }
                return toSearchResult(/*value*/ undefined);
            }

            if (state.traceEnabled) {
                trace(state.host,
                    Diagnostics.Using_0_subpath_1_with_target_2,
                    isImports ? "imports" : "exports",
                    key,
                    pattern ? target.replace(/\*/g, subpath) : target + subpath);
            }
            const finalPath = toAbsolutePath(pattern ? resolvedTarget.replace(/\*/g, subpath) : resolvedTarget + subpath);
            const inputLink = tryLoadInputFileForPath(finalPath, subpath, combinePaths(scope.packageDirectory, "package.json"), isImports);
            if (inputLink) return inputLink;
            return toSearchResult(withPackageId(scope, loadFileNameFromPackageJsonField(extensions, finalPath, /*onlyRecordFailures*/ false, state)));
        }
        else if (typeof target === "object" && target !== null) { // eslint-disable-line no-null/no-null
            if (!Array.isArray(target)) {
                traceIfEnabled(state, Diagnostics.Entering_conditional_exports);
                for (const condition of getOwnKeys(target as MapLike<unknown>)) {
                    if (condition === "default" || state.conditions.indexOf(condition) >= 0 || isApplicableVersionedTypesKey(state.conditions, condition)) {
                        traceIfEnabled(state, Diagnostics.Matched_0_condition_1, isImports ? "imports" : "exports", condition);
                        const subTarget = (target as MapLike<unknown>)[condition];
                        const result = loadModuleFromTargetImportOrExport(subTarget, subpath, pattern, key);
                        if (result) {
                            traceIfEnabled(state, Diagnostics.Resolved_under_condition_0, condition);
                            traceIfEnabled(state, Diagnostics.Exiting_conditional_exports);
                            return result;
                        }
                        else {
                            traceIfEnabled(state, Diagnostics.Failed_to_resolve_under_condition_0, condition);
                        }
                    }
                    else {
                        traceIfEnabled(state, Diagnostics.Saw_non_matching_condition_0, condition);
                    }
                }
                traceIfEnabled(state, Diagnostics.Exiting_conditional_exports);
                return undefined;
            }
            else {
                if (!length(target)) {
                    if (state.traceEnabled) {
                        trace(state.host, Diagnostics.package_json_scope_0_has_invalid_type_for_target_of_specifier_1, scope.packageDirectory, moduleName);
                    }
                    return toSearchResult(/*value*/ undefined);
                }
                for (const elem of target) {
                    const result = loadModuleFromTargetImportOrExport(elem, subpath, pattern, key);
                    if (result) {
                        return result;
                    }
                }
            }
        }
        else if (target === null) { // eslint-disable-line no-null/no-null
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.package_json_scope_0_explicitly_maps_specifier_1_to_null, scope.packageDirectory, moduleName);
            }
            return toSearchResult(/*value*/ undefined);
        }
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.package_json_scope_0_has_invalid_type_for_target_of_specifier_1, scope.packageDirectory, moduleName);
        }
        return toSearchResult(/*value*/ undefined);

        function toAbsolutePath(path: string): string;
        function toAbsolutePath(path: string | undefined): string | undefined;
        function toAbsolutePath(path: string | undefined): string | undefined {
            if (path === undefined) return path;
            return getNormalizedAbsolutePath(path, state.host.getCurrentDirectory?.());
        }

        function combineDirectoryPath(root: string, dir: string) {
            return ensureTrailingDirectorySeparator(combinePaths(root, dir));
        }

        function tryLoadInputFileForPath(finalPath: string, entry: string, packagePath: string, isImports: boolean) {
            // Replace any references to outputs for files in the program with the input files to support package self-names used with outDir
            // PROBLEM: We don't know how to calculate the output paths yet, because the "common source directory" we use as the base of the file structure
            // we reproduce into the output directory is based on the set of input files, which we're still in the process of traversing and resolving!
            // _Given that_, we have to guess what the base of the output directory is (obviously the user wrote the export map, so has some idea what it is!).
            // We are going to probe _so many_ possible paths. We limit where we'll do this to try to reduce the possibilities of false positive lookups.
            if (!state.isConfigLookup
                && (state.compilerOptions.declarationDir || state.compilerOptions.outDir)
                && finalPath.indexOf("/node_modules/") === -1
                && (state.compilerOptions.configFile ? containsPath(scope.packageDirectory, toAbsolutePath(state.compilerOptions.configFile.fileName), !useCaseSensitiveFileNames(state)) : true)
            ) {
                // So that all means we'll only try these guesses for files outside `node_modules` in a directory where the `package.json` and `tsconfig.json` are siblings.
                // Even with all that, we still don't know if the root of the output file structure will be (relative to the package file)
                // `.`, `./src` or any other deeper directory structure. (If project references are used, it's definitely `.` by fiat, so that should be pretty common.)

                const getCanonicalFileName = hostGetCanonicalFileName({ useCaseSensitiveFileNames: () => useCaseSensitiveFileNames(state) });
                const commonSourceDirGuesses: string[] = [];
                // A `rootDir` compiler option strongly indicates the root location
                // A `composite` project is using project references and has it's common src dir set to `.`, so it shouldn't need to check any other locations
                if (state.compilerOptions.rootDir || (state.compilerOptions.composite && state.compilerOptions.configFilePath)) {
                    const commonDir = toAbsolutePath(getCommonSourceDirectory(state.compilerOptions, () => [], state.host.getCurrentDirectory?.() || "", getCanonicalFileName));
                    commonSourceDirGuesses.push(commonDir);
                }
                else if (state.requestContainingDirectory) {
                    // However without either of those set we're in the dark. Let's say you have
                    //
                    // ./tools/index.ts
                    // ./src/index.ts
                    // ./dist/index.js
                    // ./package.json <-- references ./dist/index.js
                    // ./tsconfig.json <-- loads ./src/index.ts
                    //
                    // How do we know `./src` is the common src dir, and not `./tools`, given only the `./dist` out dir and `./dist/index.js` filename?
                    // Answer: We... don't. We know we're looking for an `index.ts` input file, but we have _no clue_ which subfolder it's supposed to be loaded from
                    // without more context.
                    // But we do have more context! Just a tiny bit more! We're resolving an import _for some other input file_! And that input file, too
                    // must be inside the common source directory! So we propagate that tidbit of info all the way to here via state.requestContainingDirectory

                    const requestingFile = toAbsolutePath(combinePaths(state.requestContainingDirectory, "index.ts"));
                    // And we can try every folder above the common folder for the request folder and the config/package base directory
                    // This technically can be wrong - we may load ./src/index.ts when ./src/sub/index.ts was right because we don't
                    // know if only `./src/sub` files were loaded by the program; but this has the best chance to be right of just about anything
                    // else we have. And, given that we're about to load `./src/index.ts` because we choose it as likely correct, there will then
                    // be a file outside of `./src/sub` in the program (the file we resolved to), making us de-facto right. So this fallback lookup
                    // logic may influence what files are pulled in by self-names, which in turn influences the output path shape, but it's all
                    // internally consistent so the paths should be stable so long as we prefer the "most general" (meaning: top-most-level directory) possible results first.
                    const commonDir = toAbsolutePath(getCommonSourceDirectory(state.compilerOptions, () => [requestingFile, toAbsolutePath(packagePath)], state.host.getCurrentDirectory?.() || "", getCanonicalFileName));
                    commonSourceDirGuesses.push(commonDir);

                    let fragment = ensureTrailingDirectorySeparator(commonDir);
                    while (fragment && fragment.length > 1) {
                        const parts = getPathComponents(fragment);
                        parts.pop(); // remove a directory
                        const commonDir = getPathFromPathComponents(parts);
                        commonSourceDirGuesses.unshift(commonDir);
                        fragment = ensureTrailingDirectorySeparator(commonDir);
                    }
                }
                if (commonSourceDirGuesses.length > 1) {
                    state.reportDiagnostic(createCompilerDiagnostic(
                        isImports
                            ? Diagnostics.The_project_root_is_ambiguous_but_is_required_to_resolve_import_map_entry_0_in_file_1_Supply_the_rootDir_compiler_option_to_disambiguate
                            : Diagnostics.The_project_root_is_ambiguous_but_is_required_to_resolve_export_map_entry_0_in_file_1_Supply_the_rootDir_compiler_option_to_disambiguate,
                        entry === "" ? "." : entry, // replace empty string with `.` - the reverse of the operation done when entries are built - so main entrypoint errors don't look weird
                        packagePath
                    ));
                }
                for (const commonSourceDirGuess of commonSourceDirGuesses) {
                    const candidateDirectories = getOutputDirectoriesForBaseDirectory(commonSourceDirGuess);
                    for (const candidateDir of candidateDirectories) {
                        if (containsPath(candidateDir, finalPath, !useCaseSensitiveFileNames(state))) {
                            // The matched export is looking up something in either the out declaration or js dir, now map the written path back into the source dir and source extension
                            const pathFragment = finalPath.slice(candidateDir.length + 1); // +1 to also remove directory seperator
                            const possibleInputBase = combinePaths(commonSourceDirGuess, pathFragment);
                            const jsAndDtsExtensions = [Extension.Mjs, Extension.Cjs, Extension.Js, Extension.Json, Extension.Dmts, Extension.Dcts, Extension.Dts];
                            for (const ext of jsAndDtsExtensions) {
                                if (fileExtensionIs(possibleInputBase, ext)) {
                                    const inputExts = getPossibleOriginalInputExtensionForExtension(possibleInputBase);
                                    for (const possibleExt of inputExts) {
                                        if (!extensionIsOk(extensions, possibleExt)) continue;
                                        const possibleInputWithInputExtension = changeAnyExtension(possibleInputBase, possibleExt, ext, !useCaseSensitiveFileNames(state));
                                        if (state.host.fileExists(possibleInputWithInputExtension)) {
                                            return toSearchResult(withPackageId(scope, loadFileNameFromPackageJsonField(extensions, possibleInputWithInputExtension, /*onlyRecordFailures*/ false, state)));
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
            return undefined;

            function getOutputDirectoriesForBaseDirectory(commonSourceDirGuess: string) {
                // Config file ouput paths are processed to be relative to the host's current directory, while
                // otherwise the paths are resolved relative to the common source dir the compiler puts together
                const currentDir = state.compilerOptions.configFile ? state.host.getCurrentDirectory?.() || "" : commonSourceDirGuess;
                const candidateDirectories = [];
                if (state.compilerOptions.declarationDir) {
                    candidateDirectories.push(toAbsolutePath(combineDirectoryPath(currentDir, state.compilerOptions.declarationDir)));
                }
                if (state.compilerOptions.outDir && state.compilerOptions.outDir !== state.compilerOptions.declarationDir) {
                    candidateDirectories.push(toAbsolutePath(combineDirectoryPath(currentDir, state.compilerOptions.outDir)));
                }
                return candidateDirectories;
            }
        }
    }
}

/** @internal */
export function isApplicableVersionedTypesKey(conditions: readonly string[], key: string) {
    if (conditions.indexOf("types") === -1) return false; // only apply versioned types conditions if the types condition is applied
    if (!startsWith(key, "types@")) return false;
    const range = VersionRange.tryParse(key.substring("types@".length));
    if (!range) return false;
    return range.test(version);
}

function loadModuleFromNearestNodeModulesDirectory(extensions: Extensions, moduleName: string, directory: string, state: ModuleResolutionState, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined): SearchResult<Resolved> {
    return loadModuleFromNearestNodeModulesDirectoryWorker(extensions, moduleName, directory, state, /*typesScopeOnly*/ false, cache, redirectedReference);
}

function loadModuleFromNearestNodeModulesDirectoryTypesScope(moduleName: string, directory: string, state: ModuleResolutionState): SearchResult<Resolved> {
    // Extensions parameter here doesn't actually matter, because typesOnly ensures we're just doing @types lookup, which is always DtsOnly.
    return loadModuleFromNearestNodeModulesDirectoryWorker(Extensions.Declaration, moduleName, directory, state, /*typesScopeOnly*/ true, /*cache*/ undefined, /*redirectedReference*/ undefined);
}

function loadModuleFromNearestNodeModulesDirectoryWorker(extensions: Extensions, moduleName: string, directory: string, state: ModuleResolutionState, typesScopeOnly: boolean, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined): SearchResult<Resolved> {
    const mode = state.features === 0 ? undefined : state.features & NodeResolutionFeatures.EsmMode ? ModuleKind.ESNext : ModuleKind.CommonJS;
    // Do (up to) two passes through node_modules:
    //   1. For each ancestor node_modules directory, try to find:
    //      i.  TS/DTS files in the implementation package
    //      ii. DTS files in the @types package
    //   2. For each ancestor node_modules directory, try to find:
    //      i.  JS files in the implementation package
    const priorityExtensions = extensions & (Extensions.TypeScript | Extensions.Declaration);
    const secondaryExtensions = extensions & ~(Extensions.TypeScript | Extensions.Declaration);
    // (1)
    if (priorityExtensions) {
        traceIfEnabled(state, Diagnostics.Searching_all_ancestor_node_modules_directories_for_preferred_extensions_Colon_0, formatExtensions(priorityExtensions));
        const result = lookup(priorityExtensions);
        if (result) return result;
    }
    // (2)
    if (secondaryExtensions && !typesScopeOnly) {
        traceIfEnabled(state, Diagnostics.Searching_all_ancestor_node_modules_directories_for_fallback_extensions_Colon_0, formatExtensions(secondaryExtensions));
        return lookup(secondaryExtensions);
    }

    function lookup(extensions: Extensions) {
        return forEachAncestorDirectory(normalizeSlashes(directory), ancestorDirectory => {
            if (getBaseFileName(ancestorDirectory) !== "node_modules") {
                const resolutionFromCache = tryFindNonRelativeModuleNameInCache(cache, moduleName, mode, ancestorDirectory, redirectedReference, state);
                if (resolutionFromCache) {
                    return resolutionFromCache;
                }
                return toSearchResult(loadModuleFromImmediateNodeModulesDirectory(extensions, moduleName, ancestorDirectory, state, typesScopeOnly, cache, redirectedReference));
            }
        });
    }
}

function loadModuleFromImmediateNodeModulesDirectory(extensions: Extensions, moduleName: string, directory: string, state: ModuleResolutionState, typesScopeOnly: boolean, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined): Resolved | undefined {
    const nodeModulesFolder = combinePaths(directory, "node_modules");
    const nodeModulesFolderExists = directoryProbablyExists(nodeModulesFolder, state.host);
    if (!nodeModulesFolderExists && state.traceEnabled) {
        trace(state.host, Diagnostics.Directory_0_does_not_exist_skipping_all_lookups_in_it, nodeModulesFolder);
    }

    if (!typesScopeOnly) {
        const packageResult = loadModuleFromSpecificNodeModulesDirectory(extensions, moduleName, nodeModulesFolder, nodeModulesFolderExists, state, cache, redirectedReference);
        if (packageResult) {
            return packageResult;
        }
    }

    if (extensions & Extensions.Declaration) {
        const nodeModulesAtTypes = combinePaths(nodeModulesFolder, "@types");
        let nodeModulesAtTypesExists = nodeModulesFolderExists;
        if (nodeModulesFolderExists && !directoryProbablyExists(nodeModulesAtTypes, state.host)) {
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.Directory_0_does_not_exist_skipping_all_lookups_in_it, nodeModulesAtTypes);
            }
            nodeModulesAtTypesExists = false;
        }
        return loadModuleFromSpecificNodeModulesDirectory(Extensions.Declaration, mangleScopedPackageNameWithTrace(moduleName, state), nodeModulesAtTypes, nodeModulesAtTypesExists, state, cache, redirectedReference);
    }
}

function loadModuleFromSpecificNodeModulesDirectory(extensions: Extensions, moduleName: string, nodeModulesDirectory: string, nodeModulesDirectoryExists: boolean, state: ModuleResolutionState, cache: ModuleResolutionCache | undefined, redirectedReference: ResolvedProjectReference | undefined): Resolved | undefined {
    const candidate = normalizePath(combinePaths(nodeModulesDirectory, moduleName));
    const { packageName, rest } = parsePackageName(moduleName);
    const packageDirectory = combinePaths(nodeModulesDirectory, packageName);

    let rootPackageInfo: PackageJsonInfo | undefined;
    // First look for a nested package.json, as in `node_modules/foo/bar/package.json`.
    let packageInfo = getPackageJsonInfo(candidate, !nodeModulesDirectoryExists, state);
    // But only if we're not respecting export maps (if we are, we might redirect around this location)
    if (rest !== "" && packageInfo && (
        !(state.features & NodeResolutionFeatures.Exports) ||
        !hasProperty((rootPackageInfo = getPackageJsonInfo(packageDirectory, !nodeModulesDirectoryExists, state))?.contents.packageJsonContent ?? emptyArray, "exports")
    )) {
        const fromFile = loadModuleFromFile(extensions, candidate, !nodeModulesDirectoryExists, state);
        if (fromFile) {
            return noPackageId(fromFile);
        }

        const fromDirectory = loadNodeModuleFromDirectoryWorker(
            extensions,
            candidate,
            !nodeModulesDirectoryExists,
            state,
            packageInfo.contents.packageJsonContent,
            getVersionPathsOfPackageJsonInfo(packageInfo, state),
        );
        return withPackageId(packageInfo, fromDirectory);
    }

    const loader: ResolutionKindSpecificLoader = (extensions, candidate, onlyRecordFailures, state) => {
        let pathAndExtension =
            (rest || !(state.features & NodeResolutionFeatures.EsmMode)) && loadModuleFromFile(extensions, candidate, onlyRecordFailures, state) ||
            loadNodeModuleFromDirectoryWorker(
                extensions,
                candidate,
                onlyRecordFailures,
                state,
                packageInfo && packageInfo.contents.packageJsonContent,
                packageInfo && getVersionPathsOfPackageJsonInfo(packageInfo, state),
            );
        if (
            !pathAndExtension && packageInfo
            // eslint-disable-next-line no-null/no-null
            && (packageInfo.contents.packageJsonContent.exports === undefined || packageInfo.contents.packageJsonContent.exports === null)
            && state.features & NodeResolutionFeatures.EsmMode
        ) {
            // EsmMode disables index lookup in `loadNodeModuleFromDirectoryWorker` generally, however non-relative package resolutions still assume
            // a default `index.js` entrypoint if no `main` or `exports` are present
            pathAndExtension = loadModuleFromFile(extensions, combinePaths(candidate, "index.js"), onlyRecordFailures, state);
        }
        return withPackageId(packageInfo, pathAndExtension);
    };

    if (rest !== "") {
        // Previous `packageInfo` may have been from a nested package.json; ensure we have the one from the package root now.
        packageInfo = rootPackageInfo ?? getPackageJsonInfo(packageDirectory, !nodeModulesDirectoryExists, state);
    }
    // package exports are higher priority than file/directory/typesVersions lookups and (and, if there's exports present, blocks them)
    if (packageInfo && packageInfo.contents.packageJsonContent.exports && state.features & NodeResolutionFeatures.Exports) {
        return loadModuleFromExports(packageInfo, extensions, combinePaths(".", rest), state, cache, redirectedReference)?.value;
    }
    const versionPaths = rest !== "" && packageInfo ? getVersionPathsOfPackageJsonInfo(packageInfo, state) : undefined;
    if (versionPaths) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.package_json_has_a_typesVersions_entry_0_that_matches_compiler_version_1_looking_for_a_pattern_to_match_module_name_2, versionPaths.version, version, rest);
        }
        const packageDirectoryExists = nodeModulesDirectoryExists && directoryProbablyExists(packageDirectory, state.host);
        const fromPaths = tryLoadModuleUsingPaths(extensions, rest, packageDirectory, versionPaths.paths, /*pathPatterns*/ undefined, loader, !packageDirectoryExists, state);
        if (fromPaths) {
            return fromPaths.value;
        }
    }
    return loader(extensions, candidate, !nodeModulesDirectoryExists, state);
}

function tryLoadModuleUsingPaths(extensions: Extensions, moduleName: string, baseDirectory: string, paths: MapLike<string[]>, pathPatterns: readonly (string | Pattern)[] | undefined, loader: ResolutionKindSpecificLoader, onlyRecordFailures: boolean, state: ModuleResolutionState): SearchResult<Resolved> {
    pathPatterns ||= tryParsePatterns(paths);
    const matchedPattern = matchPatternOrExact(pathPatterns, moduleName);
    if (matchedPattern) {
        const matchedStar = isString(matchedPattern) ? undefined : matchedText(matchedPattern, moduleName);
        const matchedPatternText = isString(matchedPattern) ? matchedPattern : patternText(matchedPattern);
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Module_name_0_matched_pattern_1, moduleName, matchedPatternText);
        }
        const resolved = forEach(paths[matchedPatternText], subst => {
            const path = matchedStar ? subst.replace("*", matchedStar) : subst;
            // When baseUrl is not specified, the command line parser resolves relative paths to the config file location.
            const candidate = normalizePath(combinePaths(baseDirectory, path));
            if (state.traceEnabled) {
                trace(state.host, Diagnostics.Trying_substitution_0_candidate_module_location_Colon_1, subst, path);
            }
            // A path mapping may have an extension, in contrast to an import, which should omit it.
            const extension = tryGetExtensionFromPath(subst);
            if (extension !== undefined) {
                const path = tryFile(candidate, onlyRecordFailures, state);
                if (path !== undefined) {
                    return noPackageId({ path, ext: extension, resolvedUsingTsExtension: undefined });
                }
            }
            return loader(extensions, candidate, onlyRecordFailures || !directoryProbablyExists(getDirectoryPath(candidate), state.host), state);
        });
        return { value: resolved };
    }
}

/** Double underscores are used in DefinitelyTyped to delimit scoped packages. */
const mangledScopedPackageSeparator = "__";

/** For a scoped package, we must look in `@types/foo__bar` instead of `@types/@foo/bar`. */
function mangleScopedPackageNameWithTrace(packageName: string, state: ModuleResolutionState): string {
    const mangled = mangleScopedPackageName(packageName);
    if (state.traceEnabled && mangled !== packageName) {
        trace(state.host, Diagnostics.Scoped_package_detected_looking_in_0, mangled);
    }
    return mangled;
}

/** @internal */
export function getTypesPackageName(packageName: string): string {
    return `@types/${mangleScopedPackageName(packageName)}`;
}

/** @internal */
export function mangleScopedPackageName(packageName: string): string {
    if (startsWith(packageName, "@")) {
        const replaceSlash = packageName.replace(directorySeparator, mangledScopedPackageSeparator);
        if (replaceSlash !== packageName) {
            return replaceSlash.slice(1); // Take off the "@"
        }
    }
    return packageName;
}

/** @internal */
export function getPackageNameFromTypesPackageName(mangledName: string): string {
    const withoutAtTypePrefix = removePrefix(mangledName, "@types/");
    if (withoutAtTypePrefix !== mangledName) {
        return unmangleScopedPackageName(withoutAtTypePrefix);
    }
    return mangledName;
}

/** @internal */
export function unmangleScopedPackageName(typesPackageName: string): string {
    return stringContains(typesPackageName, mangledScopedPackageSeparator) ?
        "@" + typesPackageName.replace(mangledScopedPackageSeparator, directorySeparator) :
        typesPackageName;
}

function tryFindNonRelativeModuleNameInCache(cache: NonRelativeModuleNameResolutionCache | undefined, moduleName: string, mode: ResolutionMode, containingDirectory: string, redirectedReference: ResolvedProjectReference | undefined, state: ModuleResolutionState): SearchResult<Resolved> {
    const result = cache && cache.getFromNonRelativeNameCache(moduleName, mode, containingDirectory, redirectedReference);
    if (result) {
        if (state.traceEnabled) {
            trace(state.host, Diagnostics.Resolution_for_module_0_was_found_in_cache_from_location_1, moduleName, containingDirectory);
        }
        state.resultFromCache = result;
        return {
            value: result.resolvedModule && {
                path: result.resolvedModule.resolvedFileName,
                originalPath: result.resolvedModule.originalPath || true,
                extension: result.resolvedModule.extension,
                packageId: result.resolvedModule.packageId,
                resolvedUsingTsExtension: result.resolvedModule.resolvedUsingTsExtension
            }
        };
    }
}

export function classicNameResolver(moduleName: string, containingFile: string, compilerOptions: CompilerOptions, host: ModuleResolutionHost, cache?: NonRelativeModuleNameResolutionCache, redirectedReference?: ResolvedProjectReference): ResolvedModuleWithFailedLookupLocations {
    const traceEnabled = isTraceEnabled(compilerOptions, host);
    const failedLookupLocations: string[] = [];
    const affectingLocations: string[] = [];
    const containingDirectory = getDirectoryPath(containingFile);
    const diagnostics: Diagnostic[] = [];
    const state: ModuleResolutionState = {
        compilerOptions,
        host,
        traceEnabled,
        failedLookupLocations,
        affectingLocations, packageJsonInfoCache: cache,
        features: NodeResolutionFeatures.None,
        conditions: [],
        requestContainingDirectory: containingDirectory,
        reportDiagnostic: diag => void diagnostics.push(diag),
        isConfigLookup: false,
        candidateIsFromPackageJsonField: false,
    };

    const resolved =
        tryResolve(Extensions.TypeScript | Extensions.Declaration) ||
        tryResolve(Extensions.JavaScript | (compilerOptions.resolveJsonModule ? Extensions.Json : 0));
    // No originalPath because classic resolution doesn't resolve realPath
    return createResolvedModuleWithFailedLookupLocationsHandlingSymlink(
        moduleName,
        resolved && resolved.value,
        resolved?.value && pathContainsNodeModules(resolved.value.path),
        failedLookupLocations,
        affectingLocations,
        diagnostics,
        state,
    );

    function tryResolve(extensions: Extensions): SearchResult<Resolved> {
        const resolvedUsingSettings = tryLoadModuleUsingOptionalResolutionSettings(extensions, moduleName, containingDirectory, loadModuleFromFileNoPackageId, state);
        if (resolvedUsingSettings) {
            return { value: resolvedUsingSettings };
        }

        if (!isExternalModuleNameRelative(moduleName)) {
            // Climb up parent directories looking for a module.
            const resolved = forEachAncestorDirectory(containingDirectory, directory => {
                const resolutionFromCache = tryFindNonRelativeModuleNameInCache(cache, moduleName, /*mode*/ undefined, directory, redirectedReference, state);
                if (resolutionFromCache) {
                    return resolutionFromCache;
                }
                const searchName = normalizePath(combinePaths(directory, moduleName));
                return toSearchResult(loadModuleFromFileNoPackageId(extensions, searchName, /*onlyRecordFailures*/ false, state));
            });
            if (resolved) return resolved;
            if (extensions & (Extensions.TypeScript | Extensions.Declaration)) {
                // If we didn't find the file normally, look it up in @types.
                let resolved = loadModuleFromNearestNodeModulesDirectoryTypesScope(moduleName, containingDirectory, state);
                if (extensions & Extensions.Declaration) resolved ??= resolveFromTypeRoot(moduleName, state);
                return resolved;
            }
        }
        else {
            const candidate = normalizePath(combinePaths(containingDirectory, moduleName));
            return toSearchResult(loadModuleFromFileNoPackageId(extensions, candidate, /*onlyRecordFailures*/ false, state));
        }
    }
}

function resolveFromTypeRoot(moduleName: string, state: ModuleResolutionState) {
    if (!state.compilerOptions.typeRoots) return;
    for (const typeRoot of state.compilerOptions.typeRoots) {
        const candidate = getCandidateFromTypeRoot(typeRoot, moduleName, state);
        const directoryExists = directoryProbablyExists(typeRoot, state.host);
        if (!directoryExists && state.traceEnabled) {
            trace(state.host, Diagnostics.Directory_0_does_not_exist_skipping_all_lookups_in_it, typeRoot);
        }
        const resolvedFromFile = loadModuleFromFile(Extensions.Declaration, candidate, !directoryExists, state);
        if (resolvedFromFile) {
            const packageDirectory = parseNodeModuleFromPath(resolvedFromFile.path);
            const packageInfo = packageDirectory ? getPackageJsonInfo(packageDirectory, /*onlyRecordFailures*/ false, state) : undefined;
            return toSearchResult(withPackageId(packageInfo, resolvedFromFile));
        }
        const resolved = loadNodeModuleFromDirectory(Extensions.Declaration, candidate, !directoryExists, state);
        if (resolved) return toSearchResult(resolved);
    }
}

// Program errors validate that `noEmit` or `emitDeclarationOnly` is also set,
// so this function doesn't check them to avoid propagating errors.
/** @internal */
export function shouldAllowImportingTsExtension(compilerOptions: CompilerOptions, fromFileName?: string) {
    return !!compilerOptions.allowImportingTsExtensions || fromFileName && isDeclarationFileName(fromFileName);
}

/**
 * A host may load a module from a global cache of typings.
 * This is the minumum code needed to expose that functionality; the rest is in the host.
 *
 * @internal
 */
export function loadModuleFromGlobalCache(moduleName: string, projectName: string | undefined, compilerOptions: CompilerOptions, host: ModuleResolutionHost, globalCache: string, packageJsonInfoCache: PackageJsonInfoCache): ResolvedModuleWithFailedLookupLocations {
    const traceEnabled = isTraceEnabled(compilerOptions, host);
    if (traceEnabled) {
        trace(host, Diagnostics.Auto_discovery_for_typings_is_enabled_in_project_0_Running_extra_resolution_pass_for_module_1_using_cache_location_2, projectName, moduleName, globalCache);
    }
    const failedLookupLocations: string[] = [];
    const affectingLocations: string[] = [];
    const diagnostics: Diagnostic[] = [];
    const state: ModuleResolutionState = {
        compilerOptions,
        host,
        traceEnabled,
        failedLookupLocations,
        affectingLocations,
        packageJsonInfoCache,
        features: NodeResolutionFeatures.None,
        conditions: [],
        requestContainingDirectory: undefined,
        reportDiagnostic: diag => void diagnostics.push(diag),
        isConfigLookup: false,
        candidateIsFromPackageJsonField: false,
    };
    const resolved = loadModuleFromImmediateNodeModulesDirectory(Extensions.Declaration, moduleName, globalCache, state, /*typesScopeOnly*/ false, /*cache*/ undefined, /*redirectedReference*/ undefined);
    return createResolvedModuleWithFailedLookupLocations(
        resolved,
        /*isExternalLibraryImport*/ true,
        failedLookupLocations,
        affectingLocations,
        diagnostics,
        state.resultFromCache
    );
}

/**
 * Represents result of search. Normally when searching among several alternatives we treat value `undefined` as indicator
 * that search fails and we should try another option.
 * However this does not allow us to represent final result that should be used instead of further searching (i.e. a final result that was found in cache).
 * SearchResult is used to deal with this issue, its values represents following outcomes:
 * - undefined - not found, continue searching
 * - { value: undefined } - not found - stop searching
 * - { value: <some-value> } - found - stop searching
 */
type SearchResult<T> = { value: T | undefined } | undefined;

/**
 * Wraps value to SearchResult.
 * @returns undefined if value is undefined or { value } otherwise
 */
function toSearchResult<T>(value: T | undefined): SearchResult<T> {
    return value !== undefined ? { value } : undefined;
}

function traceIfEnabled(state: ModuleResolutionState, diagnostic: DiagnosticMessage, ...args: string[]) {
    if (state.traceEnabled) {
        trace(state.host, diagnostic, ...args);
    }
}

function useCaseSensitiveFileNames(state: ModuleResolutionState) {
    return !state.host.useCaseSensitiveFileNames ? true :
        typeof state.host.useCaseSensitiveFileNames === "boolean" ? state.host.useCaseSensitiveFileNames :
        state.host.useCaseSensitiveFileNames();
}