fix(dts-plugin): prevent sibling package path prefix false positive in getDependentFiles

[hpello]

Description

getDependentFiles filters the TypeScript program's source files to only keep those that live under the project's rootDir:

.filter((file) => !file.endsWith('.d.ts') && file.startsWith(rootDir));

rootDir is an absolute path with no trailing separator, e.g. /path/to/packages/business-package. The startsWith check is a plain string prefix match, which means any sibling package whose name shares the same prefix will incorrectly pass the filter.

Concrete example from our monorepo

packages/business-package/        ← rootDir
packages/business-package-api/    ← sibling, different package

'/…/packages/business-package-api/src/index.ts'.startsWith('/…/packages/business-package') → true

All source files from business-package-api end up in filesToCompile. The generated temp tsconfig then lists them under files but with rootDir set to packages/business-package/. TypeScript considers those files outside rootDir and emits their .d.ts declarations next to their source files instead of into outDir — polluting the sibling package's src/ directory with untracked build artefacts.

Fix

Append '/' to rootDir before the startsWith check so the comparison is a true path-prefix match rather than a string-prefix match.

Note: path.sep is not used here because TypeScript normalises all file paths to forward slashes internally regardless of OS, so hardcoding '/' is both correct and portable.

Related Issue

No existing issue — discovered while migrating a Module Federation producer from Vite to Rsbuild and enabling DTS generation in build mode.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated the documentation.

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