Exposing canonical filename logic

[HoldYourWaffle]

Search Terms

canonical filename

Suggestion

I'd like to re-use the get-canonical-filename logic:

TypeScript/src/compiler/core.ts

Lines 1906 to 1909 in d68295e

	export type GetCanonicalFileName = (fileName: string) => string;
	export function createGetCanonicalFileName(useCaseSensitiveFileNames: boolean): GetCanonicalFileName {
	return useCaseSensitiveFileNames ? identity : toFileNameLowerCase;
	}

Use Cases

I want to use ts.resolveModuleName and the accompanying ts.createModuleResolutionCache to resolve ImportDeclarations (as per this comment's suggestion).
createModuleResolutionCache requires a parameter getCanonicalFileName. I think it makes the most sense to use the same logic as the compiler itself here, which is the function I linked above.

I could just copy-and-paste this function, but that feels wrong and might lead to discrepancies in the future if toFileNameLowerCase (which is not exposed either) is ever updated.

Examples

const cache = ts.createModuleResolutionCache(currentDirectory, ts.createGetCanonicalFileName(true/false));
const resolved = ts.resolveModuleName(name, file, compilerOptions, host, cache);

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[sheetalkamat]

Instead of exposing createGetCanonicalFileName we need to make createModuleResolutionCache accept caseSensitive as well.

[HoldYourWaffle]

Yeah, that probably makes more sense. I assume I'd be able to use compilerHost.useCaseSensitiveFileNames to get the appropriate value?

[HoldYourWaffle]

I just noticed that CompilerHost provides access to a getCanonicalFileName method:

TypeScript/lib/typescript.d.ts

Lines 2926 to 2934 in f31b5a2

	export interface CompilerHost extends ModuleResolutionHost {
	getSourceFile(fileName: string, languageVersion: ScriptTarget, onError?: (message: string) => void, shouldCreateNewSourceFile?: boolean): SourceFile | undefined;
	getSourceFileByPath?(fileName: string, path: Path, languageVersion: ScriptTarget, onError?: (message: string) => void, shouldCreateNewSourceFile?: boolean): SourceFile | undefined;
	getCancellationToken?(): CancellationToken;
	getDefaultLibFileName(options: CompilerOptions): string;
	getDefaultLibLocation?(): string;
	writeFile: WriteFileCallback;
	getCurrentDirectory(): string;
	getCanonicalFileName(fileName: string): string;

A workaround for my specific usecase could thus be:

const host = ts.createCompilerHost(compilerOptions); //ugly, but necessary when using the transformer API (#37754)
const cache = ts.createModuleResolutionCache(currentDirectory, host.getCanonicalFileName, compilerOptions);