Make knip compatible with erasableSyntaxOnly#1541
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webpro merged 3 commits intowebpro-nl:mainfrom Feb 19, 2026
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By making knip compatible with erasableSyntaxOnly, we're making knip compatible with other systems that could potentially parse or transpile knip codebase. For example, we could: - replace `tsc` with another compiler like swc - drop `tsx` dependency from knip repository (Node.js supports TypeScript natively, but with erasable syntax only) This change also eliminates a whole class of potential bugs related to enums, namespaces legacy decorators and other syntax this setting is forbidding.
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Pull request overview
This PR enables the erasableSyntaxOnly TypeScript compiler option for the knip package, making it compatible with alternative TypeScript parsers/transpilers like swc and Node.js native TypeScript support. This change restricts the codebase to use only "erasable" TypeScript syntax that doesn't require JavaScript emit transformations.
Changes:
- Enabled
erasableSyntaxOnlyin tsconfig.json compiler options - Converted enum
CharacterCodesto a const object in ast-helpers.ts - Refactored constructor parameter properties to explicit private field declarations in three Peeker classes (YamlCatalogPeeker, PackagePeeker, JsonCatalogPeeker)
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.
Show a summary per file
| File | Description |
|---|---|
| packages/knip/tsconfig.json | Adds erasableSyntaxOnly: true to compiler options |
| packages/knip/src/typescript/ast-helpers.ts | Converts CharacterCodes enum to const object with property syntax |
| packages/knip/src/YamlCatalogPeeker.ts | Removes constructor parameter property, adds explicit private field |
| packages/knip/src/PackagePeeker.ts | Removes constructor parameter property, adds explicit private field |
| packages/knip/src/JsonCatalogPeeker.ts | Removes constructor parameter property, adds explicit private field |
…peScript version This setting is just a safeguard, so removing it does not change the output in any way and is safe for testing purposes. Without this change, older TypeScript versions throw with "Unknown compiler option 'erasableSyntaxOnly'.".
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wojtekmaj
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Feb 18, 2026
This draft PR is to showcase the potential behind webpro-nl#1541. Local results are promising: Old test results: ``` ℹ tests 245 ℹ suites 0 ℹ pass 245 ℹ fail 0 ℹ cancelled 0 ℹ skipped 0 ℹ todo 0 ℹ duration_ms 43892.244416 ``` ``` ℹ tests 324 ℹ suites 1 ℹ pass 323 ℹ fail 1 ℹ cancelled 0 ℹ skipped 0 ℹ todo 0 ℹ duration_ms 48137.8335 ``` Old log output (fragment): ``` wojciech.maj@MacBook-Pro knip % pnpm test:smoke > knip@5.83.1 test:smoke /Users/wojciech.maj/Projekty/Open source projects/knip/packages/knip > glob-bin -c "tsx --test" "test/*.test.ts" && glob-bin -c "tsx --test" "test/{plugins,util}/*.test.ts" ✔ Should handle empty named catalog entries without null pointer error (344.005667ms) ✔ Should track referenced catalog entries (package.json) (128.936166ms) ✔ Should track referenced catalog entries (package.json root) (69.343ms) ✔ Should track referenced default catalog entries (177.375916ms) ✔ Should track referenced named catalog entries (37.006291ms) ✔ Should track referenced default catalog entries (171.729875ms) ``` New test results: ``` ℹ tests 245 ℹ suites 0 ℹ pass 245 ℹ fail 0 ℹ cancelled 0 ℹ skipped 0 ℹ todo 0 ℹ duration_ms 39849.829583 ``` ``` ℹ tests 324 ℹ suites 1 ℹ pass 322 ℹ fail 2 ℹ cancelled 0 ℹ skipped 0 ℹ todo 0 ℹ duration_ms 37563.619541 ``` New log output (fragment): ``` wojciech.maj@MacBook-Pro knip % pnpm test:smoke-fast > knip@5.83.1 test:smoke-fast /Users/wojciech.maj/Projekty/Open source projects/knip/packages/knip > glob-bin -c "node --import=./register.ts --test" "test/*.test.ts" && glob-bin -c "node --import=./register.ts --test" "test/{plugins,util}/*.test.ts" ✔ Should handle empty named catalog entries without null pointer error (96.482917ms) ✔ Should track referenced catalog entries (package.json) (74.104167ms) ✔ Should track referenced catalog entries (package.json root) (57.632125ms) ✔ Should track referenced default catalog entries (126.710542ms) ✔ Should track referenced named catalog entries (60.290042ms) ✔ Should track referenced default catalog entries (126.315625ms) ```
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Great! I was also thinking of going |
Contributor
Author
Yes, I think that's a fantastic direction. Only it was too disruptive to just throw a PR at you without discussing first :D |
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🚀 This pull request is included in v5.85.0. See Release 5.85.0 for release notes. Using Knip in a commercial project? Please consider becoming a sponsor. |
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By making knip compatible with erasableSyntaxOnly, we're making knip compatible with other systems that could potentially parse or transpile knip codebase, but are unable (or rather: unwilling) to parse TS features that require JS emit changes.
For example, we could:
tscwith another compiler like swctsxdependency from knip repository (Node.js supports TypeScript natively, but with erasable syntax only)This change also eliminates a whole class of potential bugs related to enums, namespaces legacy decorators and other syntax this setting is forbidding.