[aversini]

Make React/react-dom externalization conditional on the package's declared dependencies/peerDependencies. Updates bundler.getExternals to accept packageDependencies and only mark react/react-dom as externals when present (and never externalize the package being checked). Pass package dependency info into getExternals from checkBundleSize and adjust the cache key logic to reflect user-specified externals rather than computed defaults. Update tests to cover dependency/peerDependency cases and react/react-dom self-checks, and refresh README/CLI help text to document the new "smart externalization" behavior.

[Copilot]

Pull request overview

This PR updates bundle externalization logic so that React and React-DOM are only treated as externals when they are actual dependencies/peerDependencies of the target package, and aligns cache keying and docs/CLI help with this behavior.

Changes:

• Refined getExternals to depend on a package’s declared dependencies/peerDependencies, and ensured React/React-DOM are not externalized when analyzing their own packages.
• Updated checkBundleSize, library API (getBundleStats/trend path), and CLI cache key computation to use user-specified externals (plus noExternal) rather than previously hard-coded defaults.
• Adjusted tests and README/CLI help text to cover the new “smart externalization” behavior and clarify how --external and --no-external interact with React/React-DOM.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/bundlecheck/src/parse.ts	Updated CLI flag description for --external to describe the new automatic React/React-DOM externalization behavior and removed the now-unused DEFAULT_EXTERNALS import.
packages/bundlecheck/src/index.ts	Stopped importing getExternals and changed cache key construction in getBundleStats to depend only on user-specified externals and noExternal, with updated comments and option docs to match.
packages/bundlecheck/src/bundler.ts	Reworked getExternals to conditionally include React/React-DOM based on the package’s dependencies/peerDependencies (and never for the package itself), wiring it into checkBundleSize via the computed dependency list.
packages/bundlecheck/src/__tests__/bundler.test.ts	Updated and extended tests to assert the new behavior for packages with/without React/React-DOM in dependencies/peerDependencies, including self-checks for react and cases with additional externals.
packages/bundlecheck/README.md	Documented “smart externalization” semantics, clarified noExternal behavior for both CLI and library API, and annotated examples to show when React/React-DOM appear in externals based on peer dependency declarations.