✨ Add knip for unused dependency and dead code detection

- Add check:knip using --include dependencies,exports,files
  (skips the noisy 'types' category, which produces false positives
  for libraries whose exported types are part of the public API)
- Remove tslib and type-fest (both caught as unused by knip)
- Add 'knip' to cspell word list
- No knip config file: the --include flag keeps the scope targeted
  without boilerplate, matching the 'keep it simple' principle
- Document in project-specs.md (CHECK section) and README.md

README.md

@@ -17,6 +17,7 @@ Pattern matching for TypeScript/ESM environments (F#-style, not regex).
 - **oxlint** — Rust-based linter.
 - **oxfmt** — Rust-based formatter (Prettier-compatible). Formats JS/TS, JSON/JSONC, YAML, Markdown, MDX, and more; built-in `package.json` key sorting replaces `sort-package-json`.
 - **cspell** — spell checking.
+- **knip** — finds unused dependencies, exports, and files. Scoped via `--include dependencies,exports,files` to skip the noisy `types` category (which produces false positives for libraries whose exported types are part of the public API).
 - **publint** — validates `package.json` for ESM publishing correctness. Runs on publish only (in CI), not as part of `npm run check`.
 - **@arethetypeswrong/cli** (`attw`) — validates `.d.ts` declarations against multiple module-resolution scenarios. Runs on publish only with `--profile esm-only` (the package is intentionally ESM-only).
 - **lefthook** — git pre-commit hooks.

cspell.json

@@ -18,7 +18,8 @@
         "msvc",
         "publint",
         "attw",
-        "arethetypeswrong"
+        "arethetypeswrong",
+        "knip"
     ],
     "ignorePaths": ["dist", "node_modules", "coverage", "*.svg", ".gitignore"]
 }

package.json

@@ -35,8 +35,9 @@
     },
     "scripts": {
         "build": "tsc -p tsconfig.build.json",
-        "check": "npm run check:tsc && npm run check:oxlint && npm run check:oxfmt && npm run check:cspell && npm run check:outdated",
+        "check": "npm run check:tsc && npm run check:oxlint && npm run check:oxfmt && npm run check:cspell && npm run check:knip && npm run check:outdated",
         "check:cspell": "cspell lint ${LEFTHOOK_FILES:-.}",
+        "check:knip": "knip --include dependencies,exports,files",
         "check:outdated": "check-outdated --ignore-pre-releases --ignore-packages @oxfmt/binding-darwin-arm64,@oxfmt/binding-darwin-x64,@oxfmt/binding-linux-arm64-gnu,@oxfmt/binding-linux-arm64-musl,@oxfmt/binding-linux-x64-gnu,@oxfmt/binding-linux-x64-musl,@oxfmt/binding-win32-x64-msvc,@oxlint/binding-darwin-arm64,@oxlint/binding-darwin-x64,@oxlint/binding-linux-arm64-gnu,@oxlint/binding-linux-arm64-musl,@oxlint/binding-linux-x64-gnu,@oxlint/binding-linux-x64-musl,@oxlint/binding-win32-x64-msvc",
         "check:oxfmt": "oxfmt --check ${LEFTHOOK_FILES:-.}",
         "check:oxlint": "oxlint ${LEFTHOOK_FILES:-src}",
@@ -60,12 +61,11 @@
         "check-outdated": "^3.0.0",
         "cspell": "^10.2.1",
         "expect-type": "1.4.0",
+        "knip": "^6.34.0",
         "lefthook": "^2.1.12",
         "oxfmt": "^0.66.0",
         "oxlint": "^1.81.0",
         "publint": "^0.3.24",
-        "tslib": "^2.8.1",
-        "type-fest": "^5.9.0",
         "typescript": "^7.0.2"
     },
     "optionalDependencies": {

project-specs.md

@@ -217,7 +217,7 @@ script does not belong in the standard pipeline.
 ### CHECK
 
 - `check`: Run all checks in order — `check:oxlint`, `check:oxfmt`,
-  `check:tsc`, `check:cspell`, `check:outdated`.
+  `check:tsc`, `check:cspell`, `check:knip`, `check:outdated`.
 - `check:oxlint`: `oxlint ${LEFTHOOK_FILES:-src}` — lints `src/`
   by default; when invoked from the lefthook pre-commit hook with
   `LEFTHOOK_FILES` set to the staged-files list, lints only those
@@ -239,6 +239,14 @@ script does not belong in the standard pipeline.
 - `check:cspell`: `cspell lint ${LEFTHOOK_FILES:-.}` — walks the
   project root by default; from lefthook, only the staged files.
 - `check:outdated`: `check-outdated --ignore-pre-releases --ignore-packages @oxfmt/binding-*,@oxlint/binding-*`. The oxc native bindings are declared as `optionalDependencies` so the correct one is selected per platform automatically; the `*`-platform bindings show as "not installed" on the current platform and are explicitly ignored here.
+- `check:knip`: `knip --include dependencies,exports,files` — finds
+  unused dependencies, value exports, and source files. The
+  scoped `--include` list intentionally omits the `types`
+  category, which produces systematic false positives for
+  libraries whose exported types (e.g. `Matcher`, `Pattern`) are
+  part of the public API and not consumed internally. The
+  targeted scope keeps the signal high (real unused-dep
+  detection) without config-file boilerplate.
 
 ### FIX