Use Rolldown in build-tools

[filipsobol]

🚀 Summary

Migrate the repository tooling to Rolldown and isolated declarations.

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📌 Related issues

• See https://github.com/ckeditor/ckeditor5-internal/issues/4296#issuecomment-4487231132.

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💡 Additional information

N/A

[cursor]

New declarationFiles export missing from API test

Low Severity

The declarationFiles function is newly exported from index.ts and is part of the public API, but it's not verified in the index.test.ts API surface test. The test checks all other exports (build, addBanner, bundleCss, loadSourcemaps, rawImport, splitCss, translations) but omits declarationFiles, which means a future accidental removal wouldn't be caught by this test.

 

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[psmyrek]

This is still a valid point.

[filipsobol]

The mentioned issue already has a PR that fixes it, so we may be able to remove this plugin before this PR gets merged.

[filipsobol]

The current implementation works fine when the mixins are used like this:

class FileUploader extends /* #__PURE__ */ EmitterMixin() { /* ... */ }

However, it doesn't work when we use the following approach required by TypeScript's isolated declarations:

const FileUploaderBase: EmitterMixinConstructor = /* #__PURE__ */ EmitterMixin();

class FileUploader extends FileUploaderBase { /* ... */ }

This change fixes it.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit 8fbeea9. Configure here.}

[cursor]

Declarations ignore tsconfig scope

Medium Severity

With declarations enabled, .d.ts files are generated by globbing every *.{ts,tsx,mts,cts} under path.dirname(input), not by honoring the provided tsconfig include/exclude. Files excluded from the project (or only reachable via a broader include) can still be processed or skipped incorrectly, unlike the removed TypeScript plugin.

 

^{Reviewed by Cursor Bugbot for commit 8fbeea9. Configure here.}

[filipsobol]

I think this is acceptable for this PR. The declaration plugin intentionally works from the build input directory and mirrors source files into declaration assets. The build still passes the tsconfig to Rolldown, and declarations are only enabled when the tsconfig exists.

Fully matching TypeScript project file discovery would require implementing files/include/exclude, extends, default excludes, and TypeScript glob semantics. A partial implementation would likely be more fragile than the current explicit source-directory behavior.

If this becomes necessary, we would handle it as a separate improvement.

[psmyrek]

This test fails on Windows:

 FAIL  tests/plugins/bundleCss/bundleCss.mocked.test.ts > Resolves absolute and relative CSS imports without Rolldown results
AssertionError: expected 'D:\src\components\nested\local.css' to be '/src/components/nested/local.css' // Object.is equality

Expected: "/src/components/nested/local.css"
Received: "D:\src\components\nested\local.css"

 ❯ tests/plugins/bundleCss/bundleCss.mocked.test.ts:184:5
    182|    .toBe( '/styles/absolute.css' );
    183|   expect( await options.resolver.resolve( './nested/local.css', '/src/components/source.css?inline' ) )
    184|    .toBe( '/src/components/nested/local.css' );
       |     ^
    185|
    186|   return {

I know this test wasn't added in this PR, but would it be possible to fix it here? 🙏