typescript: a dependency staged with --library keeps the declarations under its build directory

[swapnilpaliwal-sd]

Symptom

A TypeScript call into a package passed with --library stays ambiguous_unknown when the package keeps its declarations in a build directory:

• a root .d.ts that re-exports ./dist/...: only the root files were staged (one measured package: 78 methods of ~1,600 declaration files);
• a package whose every declaration is under dist/types/ (reached through an exports map types condition): no TypeScript was staged at all (0 methods), only its JavaScript.

Cause

The TypeScript analyzer walked a library root with the project skip list (dist, build, out), and detection looks for TypeScript near the top of the tree. JavaScript already distinguishes a library root (libraryRoot); TypeScript did not.

Change

• TypeScriptAnalysisOptions.libraryRoot; extractProject passes opts.library === true. A library walk keeps TS_BUILD_OUTPUT_DIRECTORIES; nested node_modules stays skipped.
• In library mode, a root no detector calls TypeScript whose package.json declares types (types / typings, or a types condition anywhere in exports) is analysed as a TypeScript project.
• The project under analysis is unchanged.

Evidence

package shape	TS methods before	after
root .d.ts re-exporting ./dist	78	8,238
declarations only under dist/types	0	218
controls (declarations at the root / in a non-build dir)	377 · 1,104 · 12,335	unchanged

On a 5-file client fixture with the libraries staged, four previously unresolved calls now resolve to library declarations (boundary_lib); unknown sites 22 → 17. The remaining unknowns are other constructs (a default import re-exported as named, a namespace re-exported through export { z }, a method on an awaited return value, a library component used as a JSX element) and are not addressed here.

Tests

• discovery: a-library-keeps-the-declarations-under-its-build-directory (control: the same tree as the project still skips dist/) and a-library-whose-declarations-all-sit-in-dist-is-typescript (control: an untyped package gets no typescript/). Both fail without the change.
• typescript-tests.ts 49/49; tsc --noEmit clean.

Cost

A library whose build directory is large stages more declaration files (one package: ~2 min, unchanged, since its JavaScript under dist/ was already walked; the TypeScript IR is 74 MB next to 3.6 GB of JavaScript IR).

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