`LanguageServiceHost.getDefaultLibFileName` is confusing

[SimonSiefke]

TypeScript Version: 3.7.2

Search Terms:
LanguageServiceHost, getDefaultLibFileName

Code

import * as ts from 'typescript';

let compilerOptions: ts.CompilerOptions = {
  allowNonTsExtensions: true,
  target: ts.ScriptTarget.Latest,
  module: ts.ModuleKind.ESNext,
  moduleResolution: ts.ModuleResolutionKind.NodeJs,
  allowJs: true
};

const serviceHost: ts.LanguageServiceHost = {
  getScriptFileNames: () => [],
  getScriptVersion: () => '0',
  getScriptSnapshot: path => ts.ScriptSnapshot.fromString(ts.sys.readFile(path)),
  getCurrentDirectory: () => '',
  getCompilationSettings: () => compilerOptions,
  getDefaultLibFileName: ts.getDefaultLibFileName, // this doesn't work
  fileExists: ts.sys.fileExists,
  readFile: ts.sys.readFile,
  readDirectory: ts.sys.readDirectory
};

Expected behavior:
I can pass ts.getDefaultLibFileName for the property getDefaultLibFileName of serviceHost.

Actual behavior:
I have to pass ts.getDefaultLibFilePath for the property getDefaultLibFileName.
When I pass ts.getDefaultLibFileName, getScriptSnapshot only has the fileName (e.g. lib.esnext.full.d.ts) as an argument instead of the full path (e.g. /home/simon/folder/node_modules/typescript/lib/lib.esnext.full.d.ts) and when getScriptSnapshot is called, it fails to read the file.

Maybe the getDefaultLibFileName property could be replaced with a getDefaultLibFilePath property, currently it is a bit confusing :/

Wiki Link: https://github.com/Microsoft/TypeScript/wiki/Using-the-Compiler-API#incremental-build-support-using-the-language-services

[fatcerberus]

I agree, that is very confusing.

[RyanCavanaugh]

This isn't worth taking a breaking change over.