Always error on property override accessor

src/compiler/checker.ts

@@ -33823,8 +33823,7 @@ namespace ts {
                     const derivedPropertyFlags = derived.flags & SymbolFlags.PropertyOrAccessor;
                     if (basePropertyFlags && derivedPropertyFlags) {
                         // property/accessor is overridden with property/accessor
-                        if (!compilerOptions.useDefineForClassFields
-                            || baseDeclarationFlags & ModifierFlags.Abstract && !(base.valueDeclaration && isPropertyDeclaration(base.valueDeclaration) && base.valueDeclaration.initializer)
+                        if (baseDeclarationFlags & ModifierFlags.Abstract && !(base.valueDeclaration && isPropertyDeclaration(base.valueDeclaration) && base.valueDeclaration.initializer)
                             || base.valueDeclaration && base.valueDeclaration.parent.kind === SyntaxKind.InterfaceDeclaration
                             || derived.valueDeclaration && isBinaryExpression(derived.valueDeclaration)) {
                             // when the base property is abstract or from an interface, base/derived flags don't need to match
@@ -33840,7 +33839,7 @@ namespace ts {
                                 Diagnostics._0_is_defined_as_a_property_in_class_1_but_is_overridden_here_in_2_as_an_accessor;
                             error(getNameOfDeclaration(derived.valueDeclaration) || derived.valueDeclaration, errorMessage, symbolToString(base), typeToString(baseType), typeToString(type));
                         }
-                        else {
+                        else if (compilerOptions.useDefineForClassFields) {
                             const uninitialized = find(derived.declarations, d => d.kind === SyntaxKind.PropertyDeclaration && !(d as PropertyDeclaration).initializer);
                             if (uninitialized
                                 && !(derived.flags & SymbolFlags.Transient)

src/compiler/diagnosticMessages.json

@@ -5705,6 +5705,10 @@
         "category": "Message",
         "code": 95118
     },
+    "Generate 'get' and 'set' accessors for all overriding properties": {
+        "category": "Message",
+        "code": 95119
+    },
 
     "No value exists in scope for the shorthand property '{0}'. Either declare one or provide an initializer.": {
         "category": "Error",

src/services/codefixes/fixAddMissingMember.ts

@@ -78,19 +78,6 @@ namespace ts.codefix {
         },
     });
 
-    function getAllSupers(decl: ClassOrInterface | undefined, checker: TypeChecker): readonly ClassOrInterface[] {
-        const res: ClassLikeDeclaration[] = [];
-        while (decl) {
-            const superElement = getClassExtendsHeritageElement(decl);
-            const superSymbol = superElement && checker.getSymbolAtLocation(superElement.expression);
-            const superDecl = superSymbol && find(superSymbol.declarations, isClassLike);
-            if (superDecl) { res.push(superDecl); }
-            decl = superDecl;
-        }
-        return res;
-    }
-
-    type ClassOrInterface = ClassLikeDeclaration | InterfaceDeclaration;
     const enum InfoKind { Enum, ClassOrInterface }
     interface EnumInfo {
         readonly kind: InfoKind.Enum;

src/services/codefixes/fixPropertyOverrideAccessor.ts

@@ -0,0 +1,57 @@
+/* @internal */
+namespace ts.codefix {
+    const errorCodes = [
+        Diagnostics._0_is_defined_as_an_accessor_in_class_1_but_is_overridden_here_in_2_as_an_instance_property.code,
+        Diagnostics._0_is_defined_as_a_property_in_class_1_but_is_overridden_here_in_2_as_an_accessor.code,
+    ];
+    const fixId = "fixPropertyOverrideAccessor";
+    registerCodeFix({
+        errorCodes,
+        getCodeActions(context) {
+            const edits = doChange(context.sourceFile, context.span.start, context.span.length, context.errorCode, context);
+            if (edits) {
+                return [createCodeFixAction(fixId, edits, Diagnostics.Generate_get_and_set_accessors, fixId, Diagnostics.Generate_get_and_set_accessors_for_all_overriding_properties)];
+            }
+        },
+        fixIds: [fixId],
+
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => {
+            const edits = doChange(diag.file, diag.start, diag.length, diag.code, context);
+            if (edits) {
+                for (const edit of edits) {
+                    changes.pushRaw(context.sourceFile, edit);
+                }
+            }
+        }),
+    });
+
+    function doChange(file: SourceFile, start: number, length: number, code: number, context: CodeFixContext | CodeFixAllContext) {
+        let startPosition: number;
+        let endPosition: number;
+        if (code === Diagnostics._0_is_defined_as_an_accessor_in_class_1_but_is_overridden_here_in_2_as_an_instance_property.code) {
+            startPosition = start;
+            endPosition = start + length;
+        }
+        else if (code === Diagnostics._0_is_defined_as_a_property_in_class_1_but_is_overridden_here_in_2_as_an_accessor.code) {
+            const checker = context.program.getTypeChecker();
+            const node = getTokenAtPosition(file, start).parent;
+            Debug.assert(isAccessor(node), "error span of fixPropertyOverrideAccessor should only be on an accessor");
+            const containingClass = node.parent;
+            Debug.assert(isClassLike(containingClass), "erroneous accessors should only be inside classes");
+            const base = singleOrUndefined(getAllSupers(containingClass, checker));
+            if (!base) return [];
+
+            const name = unescapeLeadingUnderscores(getTextOfPropertyName(node.name));
+            const baseProp = checker.getPropertyOfType(checker.getTypeAtLocation(base), name);
+            if (!baseProp || !baseProp.valueDeclaration) return [];
+
+            startPosition = baseProp.valueDeclaration.pos;
+            endPosition = baseProp.valueDeclaration.end;
+            file = getSourceFileOfNode(baseProp.valueDeclaration);
+        }
+        else {
+            Debug.fail("fixPropertyOverrideAccessor codefix got unexpected error code " + code);
+        }
+        return generateAccessorFromProperty(file, startPosition, endPosition, context, Diagnostics.Generate_get_and_set_accessors.message);
+    }
+}

src/services/codefixes/generateAccessors.ts

@@ -0,0 +1,243 @@
+/* @internal */
+namespace ts.codefix {
+    type AcceptedDeclaration = ParameterPropertyDeclaration | PropertyDeclaration | PropertyAssignment;
+    type AcceptedNameType = Identifier | StringLiteral;
+    type ContainerDeclaration = ClassLikeDeclaration | ObjectLiteralExpression;
+
+    interface Info {
+        readonly container: ContainerDeclaration;
+        readonly isStatic: boolean;
+        readonly isReadonly: boolean;
+        readonly type: TypeNode | undefined;
+        readonly declaration: AcceptedDeclaration;
+        readonly fieldName: AcceptedNameType;
+        readonly accessorName: AcceptedNameType;
+        readonly originalName: string;
+        readonly renameAccessor: boolean;
+    }
+
+    export function generateAccessorFromProperty(file: SourceFile, start: number, end: number, context: textChanges.TextChangesContext, _actionName: string): FileTextChanges[] | undefined {
+        const fieldInfo = getAccessorConvertiblePropertyAtPosition(file, start, end);
+        if (!fieldInfo) return undefined;
+
+        const changeTracker = textChanges.ChangeTracker.fromContext(context);
+        const { isStatic, isReadonly, fieldName, accessorName, originalName, type, container, declaration } = fieldInfo;
+
+        suppressLeadingAndTrailingTrivia(fieldName);
+        suppressLeadingAndTrailingTrivia(accessorName);
+        suppressLeadingAndTrailingTrivia(declaration);
+        suppressLeadingAndTrailingTrivia(container);
+
+        let accessorModifiers: ModifiersArray | undefined;
+        let fieldModifiers: ModifiersArray | undefined;
+        if (isClassLike(container)) {
+            const modifierFlags = getEffectiveModifierFlags(declaration);
+            if (isSourceFileJS(file)) {
+                const modifiers = createModifiers(modifierFlags);
+                accessorModifiers = modifiers;
+                fieldModifiers = modifiers;
+            }
+            else {
+                accessorModifiers = createModifiers(prepareModifierFlagsForAccessor(modifierFlags));
+                fieldModifiers = createModifiers(prepareModifierFlagsForField(modifierFlags));
+            }
+        }
+
+        updateFieldDeclaration(changeTracker, file, declaration, fieldName, fieldModifiers);
+
+        const getAccessor = generateGetAccessor(fieldName, accessorName, type, accessorModifiers, isStatic, container);
+        suppressLeadingAndTrailingTrivia(getAccessor);
+        insertAccessor(changeTracker, file, getAccessor, declaration, container);
+
+        if (isReadonly) {
+            // readonly modifier only existed in classLikeDeclaration
+            const constructor = getFirstConstructorWithBody(<ClassLikeDeclaration>container);
+            if (constructor) {
+                updateReadonlyPropertyInitializerStatementConstructor(changeTracker, file, constructor, fieldName.text, originalName);
+            }
+        }
+        else {
+            const setAccessor = generateSetAccessor(fieldName, accessorName, type, accessorModifiers, isStatic, container);
+            suppressLeadingAndTrailingTrivia(setAccessor);
+            insertAccessor(changeTracker, file, setAccessor, declaration, container);
+        }
+
+        return changeTracker.getChanges();
+    }
+
+    function isConvertibleName(name: DeclarationName): name is AcceptedNameType {
+        return isIdentifier(name) || isStringLiteral(name);
+    }
+
+    function isAcceptedDeclaration(node: Node): node is AcceptedDeclaration {
+        return isParameterPropertyDeclaration(node, node.parent) || isPropertyDeclaration(node) || isPropertyAssignment(node);
+    }
+
+    function createPropertyName(name: string, originalName: AcceptedNameType) {
+        return isIdentifier(originalName) ? createIdentifier(name) : createLiteral(name);
+    }
+
+    function createAccessorAccessExpression(fieldName: AcceptedNameType, isStatic: boolean, container: ContainerDeclaration) {
+        const leftHead = isStatic ? (<ClassLikeDeclaration>container).name! : createThis(); // TODO: GH#18217
+        return isIdentifier(fieldName) ? createPropertyAccess(leftHead, fieldName) : createElementAccess(leftHead, createLiteral(fieldName));
+    }
+
+    function createModifiers(modifierFlags: ModifierFlags): ModifiersArray | undefined {
+        return modifierFlags ? createNodeArray(createModifiersFromModifierFlags(modifierFlags)) : undefined;
+    }
+
+    function prepareModifierFlagsForAccessor(modifierFlags: ModifierFlags): ModifierFlags {
+        modifierFlags &= ~ModifierFlags.Readonly; // avoid Readonly modifier because it will convert to get accessor
+        modifierFlags &= ~ModifierFlags.Private;
+
+        if (!(modifierFlags & ModifierFlags.Protected)) {
+            modifierFlags |= ModifierFlags.Public;
+        }
+
+        return modifierFlags;
+    }
+
+    function prepareModifierFlagsForField(modifierFlags: ModifierFlags): ModifierFlags {
+        modifierFlags &= ~ModifierFlags.Public;
+        modifierFlags &= ~ModifierFlags.Protected;
+        modifierFlags |= ModifierFlags.Private;
+        return modifierFlags;
+    }
+
+    export function getAccessorConvertiblePropertyAtPosition(file: SourceFile, start: number, end: number): Info | undefined {
+        const node = getTokenAtPosition(file, start);
+        const declaration = findAncestor(node.parent, isAcceptedDeclaration);
+        // make sure declaration have AccessibilityModifier or Static Modifier or Readonly Modifier
+        const meaning = ModifierFlags.AccessibilityModifier | ModifierFlags.Static | ModifierFlags.Readonly;
+        if (!declaration || !nodeOverlapsWithStartEnd(declaration.name, file, start, end)
+            || !isConvertibleName(declaration.name) || (getEffectiveModifierFlags(declaration) | meaning) !== meaning) return undefined;
+
+        const name = declaration.name.text;
+        const startWithUnderscore = startsWithUnderscore(name);
+        const fieldName = createPropertyName(startWithUnderscore ? name : getUniqueName(`_${name}`, file), declaration.name);
+        const accessorName = createPropertyName(startWithUnderscore ? getUniqueName(name.substring(1), file) : name, declaration.name);
+        return {
+            isStatic: hasStaticModifier(declaration),
+            isReadonly: hasEffectiveReadonlyModifier(declaration),
+            type: getTypeAnnotationNode(declaration),
+            container: declaration.kind === SyntaxKind.Parameter ? declaration.parent.parent : declaration.parent,
+            originalName: (<AcceptedNameType>declaration.name).text,
+            declaration,
+            fieldName,
+            accessorName,
+            renameAccessor: startWithUnderscore
+        };
+    }
+
+    function generateGetAccessor(fieldName: AcceptedNameType, accessorName: AcceptedNameType, type: TypeNode | undefined, modifiers: ModifiersArray | undefined, isStatic: boolean, container: ContainerDeclaration) {
+        return createGetAccessor(
+            /*decorators*/ undefined,
+            modifiers,
+            accessorName,
+            /*parameters*/ undefined!, // TODO: GH#18217
+            type,
+            createBlock([
+                createReturn(
+                    createAccessorAccessExpression(fieldName, isStatic, container)
+                )
+            ], /*multiLine*/ true)
+        );
+    }
+
+    function generateSetAccessor(fieldName: AcceptedNameType, accessorName: AcceptedNameType, type: TypeNode | undefined, modifiers: ModifiersArray | undefined, isStatic: boolean, container: ContainerDeclaration) {
+        return createSetAccessor(
+            /*decorators*/ undefined,
+            modifiers,
+            accessorName,
+            [createParameter(
+                /*decorators*/ undefined,
+                /*modifiers*/ undefined,
+                /*dotDotDotToken*/ undefined,
+                createIdentifier("value"),
+                /*questionToken*/ undefined,
+                type
+            )],
+            createBlock([
+                createStatement(
+                    createAssignment(
+                        createAccessorAccessExpression(fieldName, isStatic, container),
+                        createIdentifier("value")
+                    )
+                )
+            ], /*multiLine*/ true)
+        );
+    }
+
+    function updatePropertyDeclaration(changeTracker: textChanges.ChangeTracker, file: SourceFile, declaration: PropertyDeclaration, fieldName: AcceptedNameType, modifiers: ModifiersArray | undefined) {
+        const property = updateProperty(
+            declaration,
+            declaration.decorators,
+            modifiers,
+            fieldName,
+            declaration.questionToken || declaration.exclamationToken,
+            declaration.type,
+            declaration.initializer
+        );
+        changeTracker.replaceNode(file, declaration, property);
+    }
+
+    function updatePropertyAssignmentDeclaration(changeTracker: textChanges.ChangeTracker, file: SourceFile, declaration: PropertyAssignment, fieldName: AcceptedNameType) {
+        const assignment = updatePropertyAssignment(declaration, fieldName, declaration.initializer);
+        changeTracker.replacePropertyAssignment(file, declaration, assignment);
+    }
+
+    function updateFieldDeclaration(changeTracker: textChanges.ChangeTracker, file: SourceFile, declaration: AcceptedDeclaration, fieldName: AcceptedNameType, modifiers: ModifiersArray | undefined) {
+        if (isPropertyDeclaration(declaration)) {
+            updatePropertyDeclaration(changeTracker, file, declaration, fieldName, modifiers);
+        }
+        else if (isPropertyAssignment(declaration)) {
+            updatePropertyAssignmentDeclaration(changeTracker, file, declaration, fieldName);
+        }
+        else {
+            changeTracker.replaceNode(file, declaration,
+                updateParameter(declaration, declaration.decorators, modifiers, declaration.dotDotDotToken, cast(fieldName, isIdentifier), declaration.questionToken, declaration.type, declaration.initializer));
+        }
+    }
+
+    function insertAccessor(changeTracker: textChanges.ChangeTracker, file: SourceFile, accessor: AccessorDeclaration, declaration: AcceptedDeclaration, container: ContainerDeclaration) {
+        isParameterPropertyDeclaration(declaration, declaration.parent) ? changeTracker.insertNodeAtClassStart(file, <ClassLikeDeclaration>container, accessor) :
+            isPropertyAssignment(declaration) ? changeTracker.insertNodeAfterComma(file, declaration, accessor) :
+            changeTracker.insertNodeAfter(file, declaration, accessor);
+    }
+
+    function updateReadonlyPropertyInitializerStatementConstructor(changeTracker: textChanges.ChangeTracker, file: SourceFile, constructor: ConstructorDeclaration, fieldName: string, originalName: string) {
+        if (!constructor.body) return;
+        constructor.body.forEachChild(function recur(node) {
+            if (isElementAccessExpression(node) &&
+                node.expression.kind === SyntaxKind.ThisKeyword &&
+                isStringLiteral(node.argumentExpression) &&
+                node.argumentExpression.text === originalName &&
+                isWriteAccess(node)) {
+                changeTracker.replaceNode(file, node.argumentExpression, createStringLiteral(fieldName));
+            }
+            if (isPropertyAccessExpression(node) && node.expression.kind === SyntaxKind.ThisKeyword && node.name.text === originalName && isWriteAccess(node)) {
+                changeTracker.replaceNode(file, node.name, createIdentifier(fieldName));
+            }
+            if (!isFunctionLike(node) && !isClassLike(node)) {
+                node.forEachChild(recur);
+            }
+        });
+    }
+
+    export function getAllSupers(decl: ClassOrInterface | undefined, checker: TypeChecker): readonly ClassOrInterface[] {
+        const res: ClassLikeDeclaration[] = [];
+        while (decl) {
+            const superElement = getClassExtendsHeritageElement(decl);
+            const superSymbol = superElement && checker.getSymbolAtLocation(superElement.expression);
+            if (!superSymbol) break;
+            const symbol = superSymbol.flags & SymbolFlags.Alias ? checker.getAliasedSymbol(superSymbol) : superSymbol;
+            const superDecl = find(symbol.declarations, isClassLike);
+            if (!superDecl) break;
+            res.push(superDecl);
+            decl = superDecl;
+        }
+        return res;
+    }
+
+    export type ClassOrInterface = ClassLikeDeclaration | InterfaceDeclaration;
+}