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Fallow’s default analysis is Rust-native, syntactic, and independent of Node.js or the TypeScript compiler. Add --type-aware when a cleanup or refactor depends on exact TypeScript symbol identity across aliases, re-exports, packages, or tests. The optional companion adds five project-wide capabilities:
  • exact symbol-use confirmation for existing dead-code candidates
  • symbol traces with namespaces, aliases, and re-export hops
  • package API surfaces and cross-file private type leaks
  • exact consumers, affected files, and targeted tests
  • advisory public-signature type coupling
Use this pass when an actual cleanup or refactor decision depends on TypeScript identity. Keep the normal syntactic run for fast everyday feedback.

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What this does not replace

Keep tsc --noEmit responsible for compiler correctness. Keep Oxlint responsible for local lint rules. Fallow does not emit TypeScript diagnostics or duplicate local typed lint findings. Type-aware fallow answers project-wide questions those tools do not:
  • Is this exact declaration used through an alias or re-export?
  • Which production files and tests depend on this exported symbol?
  • Does a public signature expose a package-private type?
  • Which public types couple packages or modules together?

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Conservative results

Every semantic result reports complete, partial, or unavailable. Fallow removes a dead-code candidate only when the checker resolves its exact declaration identity. Partial or unavailable analysis keeps the original finding and reports a stable omission reason. fallow fix --type-aware offers a class-member removal only after every owning project returns complete negative evidence and the declaration guard still matches. Always preview with --dry-run.
Checker-visible evidence is not proof that a published API has no external consumers. Keep package exports, publicPackages, visibility tags, and explicitly selected consumer projects authoritative for library boundaries.
Use --type-aware-require complete in CI when incomplete semantic evidence must fail the job:
Use repeatable --type-aware-project flags when automatic project selection does not include every consumer:

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Persistent configuration

Keep the feature opt-in per repository:
Start with best-effort. Use complete only when partial or unavailable semantic evidence must fail the run.

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Performance

Type-aware analysis constructs an additional TypeScript Program and scans checker symbols. On the current public release corpus, marginal overhead is about 92 ms at the median and 2.3 seconds at P95. Large projects can take longer. Editor sessions reuse the loaded Program, while one-shot CLI and CI runs pay the cold setup cost.

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Installation

The fallow npm package installs a version-matched optional fallow-type-aware companion. If optional dependencies are disabled, install the exact same version manually. fallow type-aware status verifies discovery, package version, protocol version, and backend version without analyzing the project.

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See also

Dead code CLI

Refine cleanup findings and run exact symbol queries.

Health CLI

Inspect advisory public-signature type coupling.

Known limitations

Understand the boundary between default syntactic and optional semantic analysis.