disable certain global types for specific files, or specify type roots for specific files.

This continues some ideas from https://github.com/microsoft/TypeScript/issues/17042, which was closed by @microsoft (for inactivity, I think?).

Search Terms

disable certain global types for specific files, specific type roots for certain files

Suggestion

Ability to specify which @types (or in general, which specified typeRoots) apply to which files in a project.

Use Cases

My project's src folder contains both .ts and .test.ts files, and I'd like an easy way for globals like describe to be defined only for the .test.ts files.

Examples

Not sure, but maybe some sort of new options in tsconfig.json for specifying which types items, lib items, or typeRoots items apply to which files.

This would be a beneficial feature because various editors (VS Code aside) look for a tsconfig.json file at the root of a project, and at the moment the only way to make types work in all files is to just provides all types for all files, which is undesirable because describe is not a function that is available in source files (as an example).

Example configuration: maybe instead of a typeRoots array, it can be an object like:

"typeRoots": {
  "./src/**/*.test.ts": ["../path/to/test/types"], // test-only types
  "./src/**/*.ts": ["../path/to/@types"] // other types other files
}

Or something. That's just an example to get the idea rolling.

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.

Start by reading the related issue #17042 and the proposal's tsconfig.json examples. Investigate how types, lib, and typeRoots currently apply to the project's src files, including .test.ts files. Done would mean a documented, implemented way to scope those type sources to selected files without affecting existing configurations.