fix(detector): stop silent dependency drops in SEA mode (ESM parse, dynamic import, decorators)

[robertsLando]

Summary

Three related fixes to lib/detector.ts (and the ESM transformer), all of which cure the same user-visible symptom: pkg logged a Babel parse has failed warning and then silently dropped the file's dependency graph, forcing users to enumerate missing files in pkg.scripts. Most visible in SEA mode, where the ESM→CJS transform is skipped and the walker's detector is the only dependency pass.

• Parse ESM files as modules. detector.parse() called babel with the default sourceType: 'script', so .mjs / type:module files using import.meta or top-level await failed to parse. Thread isESMFile(record.file) from walker.stepDetect through detect() into parse() and set sourceType: 'module' for ESM files. Per-file detection uses the existing isESMFile helper (extension + nearest package.json#type), so CJS files keep script-mode parsing.
• Walk dynamic import('literal'). Teach visitorSuccessful to match CallExpression nodes whose callee is Import with a literal first arg, returning ALIAS_AS_RESOLVABLE. Bundler-emitted chunk splits (await import('./chunk-xxx.js')) now get bundled like require() / static import … from …. Non-literal dynamic imports stay silent.
• Enable the decorators-legacy babel plugin. Third-party sources that ship raw @decorator syntax (fontkit, older MobX / Nest builds) tripped the same parse-failure → silent-drop flow. Enabling the plugin in the detector and in lib/esm-transformer.ts lets them parse cleanly. Covers both class and method decorator positions, which is what 99% of published code uses.

sourceType: 'unambiguous' was rejected for the ESM case: a file whose only ESM marker is await import(…) has no static import/export syntax, so unambiguous falls back to script mode and the original parse failure returns. The package.json type field is the authoritative signal.

lib/detector.ts also gets concise JSDoc on every visitor and helper so the next contributor doesn't have to reverse-engineer them from the AST.

Closes #264 (follow-ups filed at #269 for other detector shapes still silently dropped).

Test plan

• yarn build, yarn lint
• New test-94-sea-esm-import-meta: SEA build of a type:module app with import.meta.url, a static import, a dynamic import('./lib/dyn.mjs'), and a decorator-using file (lib/decorated.js) walked via pkg.scripts. Asserts Babel parse has failed never appears in pkg output, and the binary prints the imported values — proving all the walked files made it into the snapshot.
• Verified each of the three fixes independently. Stashing the detector parse change → ERR_MODULE_NOT_FOUND on helper.mjs; stashing the dynamic-import visitor → same miss on dyn.mjs; stashing the plugin change → Babel parse has failed: This experimental syntax requires enabling one of the following parser plugin(s) emitted for decorated.js.
• Re-ran test-85-sea-enhanced, test-87-sea-esm, test-91-sea-esm-entry, test-92-sea-tla, test-51-esm-import-meta, test-52-esm-internal-imports, test-53-esm-nested-imports — all green.

[Copilot]

Pull request overview

This PR fixes SEA-mode dependency detection regressions by improving Babel parsing and expanding the detector’s import matching so ESM graphs aren’t silently dropped after parse failures.

Changes:

• Parse walked files as ESM modules when isESMFile(...) indicates ESM, and enable decorators-legacy in both the detector and ESM transformer.
• Detect and walk dynamic import('literal') the same way as static imports / require(...).
• Add a SEA-focused regression test covering import.meta, top-level await import(...), and decorator syntax parsing.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/test.js	Registers the new SEA regression test in the host-only test list.
test/test-94-sea-esm-import-meta/main.js	New test asserting no “Babel parse has failed” warnings and validating SEA binary output.
test/test-94-sea-esm-import-meta/app/package.json	ESM fixture app (type: module) + pkg.scripts to include decorator fixture.
test/test-94-sea-esm-import-meta/app/index.mjs	Fixture using import.meta and a dynamic import('./lib/dyn.mjs').
test/test-94-sea-esm-import-meta/app/lib/helper.mjs	Static import target fixture.
test/test-94-sea-esm-import-meta/app/lib/dyn.mjs	Dynamic import target fixture.
test/test-94-sea-esm-import-meta/app/lib/decorated.js	Decorator-syntax fixture to ensure parser plugin coverage.
lib/walker.ts	Threads isESMFile(record.file) into detector.detect(...) so parsing uses the correct source type.
lib/esm-transformer.ts	Enables decorators-legacy so transformer parsing doesn’t fail on decorator syntax.
lib/detector.ts	Adds ESM-aware parsing, enables decorators-legacy, and detects dynamic import('literal').
eslint.config.js	Ignores the decorator-syntax fixture from linting.