Add a helper function to resolve module import text to a file

[mhegazy]

currently resolving a context for the language service requires calling ts.preProcessFile on all files in the context, and following references. resolving triple-slash references is simple, resolving modules is a bit more complicated, as it involves searching in containing directories until a matching .ts file is found.

As a work around, here is the resolution logic:

function resolveImport(moduleName: string, souceFilename: string, fileExists: (filename: string) => boolean): string {
        var searchPath = ts.getDirectoryPath(souceFilename);

        while (true) {
            var filename = ts.normalizePath(ts.combinePaths(searchPath, moduleName));
            if (fileExists(filename + ".ts")) return filename + ".ts";
            if (fileExists(filename + ".d.ts")) return filename + ".d.ts";

            var parentPath = ts.getDirectoryPath(searchPath);
            if (parentPath === searchPath) break;

            searchPath = parentPath;
        }

        return undefined;
    }

[mhegazy]

This should be handled by #1735

[spadgos]

The wiki links to this page.

Something that is currently missing, and should be added in next release, is a built-in way to resolve imports. ts.preProcessFile returns import text, and the caller needs to resolve that to a .ts file path. Issue #1793 tracks fixing it.

Should that be updated?

[mhegazy]

Should that be updated?

i think so.

[vivin]

@mhegazy Is there updated documentation that shows how this can be done? I'm looking to implement some custom module-resolution logic. I have it working with tsc, but I'd like the IDE to be able to resolve these modules as well without them showing up as errors.

[mhegazy]

@mhegazy Is there updated documentation that shows how this can be done? I'm looking to implement some custom module-resolution logic. I have it working with tsc, but I'd like the IDE to be able to resolve these modules as well without them showing up as errors.

IDE's use tsserver. the only way you can change the behavior there is if you create a language service plugin. you can find more docs about LS plugins in https://github.com/Microsoft/TypeScript/wiki/Writing-a-Language-Service-Plugin