fix: make plugin-kit types usable in CommonJS

[fasttime]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

This PR ensures that the plugin-kit types can be imported from a CommonJS module when moduleResolution is one of 'node16' or 'nodenext'. This is currently not possible because of the way TypeScript handles imports of ESM modules in CommonJS.

Repro

What changes did you make? (Give an overview)

Made sure that packages/plugin/dist/cjs/index.d.cts uses the "resolution-mode": "import" import attribute to import ./types.ts.

- export type StringConfig = import("./types.ts").StringConfig;
- export type BooleanConfig = import("./types.ts").BooleanConfig;
+ export type StringConfig = import("./types.ts", { with: { "resolution-mode": "import" } }).StringConfig;
+ export type BooleanConfig = import("./types.ts", { with: { "resolution-mode": "import" } }).BooleanConfig;

It's not possible to add the import attribute directly to the source code in packages/plugin-kit/src/config-comment-parser.js because then the same import attribute would appear also in the generated ESM types, and jsr does not like that (maybe because import attributes are not supported in TypeScript < 5.0).

Downloading JSR release binary...
[00:15] [#################################################>] 40.8 MiB/40.9 MiB
Checking for slow types in the public API...
error: Failed preparing '@eslint/plugin-kit'.

Caused by:
    0: Failed to create a tarball
    1: Expected '{', got 'StringConfig' at file:///.../rewrite/packages/plugin-kit/dist/esm/index.d.ts:12:13
       
         export type StringConfig = import("./types.ts", { with: { "resolution-mode": "im...
                     ~~~~~~~~~~~~
Child process exited with: 1
npm error Lifecycle script `test:jsr` failed with error:
npm error code 1
npm error path .../eslint/rewrite/packages/plugin-kit
npm error workspace @eslint/[email protected]
npm error location .../eslint/rewrite/packages/plugin-kit
npm error command failed
npm error command sh -c jsr publish --dry-run

This is not the only possible fix, see also: eslint/json#66 (comment).

Other changes included in this PR:

• Made @eslint/core a runtime dependency of @eslint/plugin-kit.
• Added tests to ensure that @eslint/core and @eslint/plugin-kit can be imported from a .cts file.
• Added type tests to @eslint/plugin-kit.

Related Issues

Is there anything you'd like reviewers to focus on?

[nzakas]

I'm curious: Will this work with TypeScript 4? And if not, does it matter?

[fasttime]

It will not work because TypeScript 4 doesn't support import attributes. The alternative would be renaming types.ts to types.cts in dist/cjs and updating the imports in index.d.cts accordingly.

Update:

• It works with TypeScript 5.0: https://stackblitz.com/edit/1bf6yn8t-pnhhhn5w
• It doesn't works with TypeScript 4.9: https://stackblitz.com/edit/1bf6yn8t-xqthsa6o

[nzakas]

I think renaming to types.cts and updating the references seems like a safer option for best compatibility. What do you think?

[fasttime]

I agree. I switched to importing from types.cts in 38bc8e9. We don't have policy about TypeScript versions support like we have for Node.js versions, but since the import attributes proposal is still not finalized, types.cts looks like a safer choice.

[nzakas]

LGTM. Would like @mdjermanovic to review before merging.

[mdjermanovic]

LGTM, thanks!