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> Re-creation of #4427 due to rebasing issues. Original attempt: #642 ----- Third time's the charm? Each time I attempt this rule, I find a bunch of bugs in `Semantic`, and I expect this attempt to be no different. Expect sidecar issues+PRs stemming from this PR here. ## Not Supported These are cases supported in the original eslint rule, but that I'm intentionally deciding not to support - export comments in scripts ```js /* exported a */ var a; ``` - global comments ```js /* global a */ var a; ``` ## Behavior Changes These are intentional deviations from the original rule's behavior: - logical re-assignments are not considered usages ```js // passes in eslint/no-unused-vars, fails in this implementation let a = 0; a ||= 1; let b = 0; b &&= 2; let c = undefined; c ??= [] ``` ## Known Limitations - Lint rules do not have babel or tsconfig information, meaning we can't determine if `React` imports are being used or not. The relevant tsconfig settings here are `jsx`, `jsxPragma`, and `jsxFragmentName`. To accommodate this, all imports to symbols named `React` or `h` are ignored in JSX files. - References to symbols used in JSDoc `{@link}` tags are not created, so symbols that are only used in doc comments will be reported as unused. See: #4443 - `.vue` files are skipped completely, since variables can be used in templates in ways we cannot detect > note: `.d.ts` files are skipped as well. ## Todo - [x] Skip unused TS enum members on used enums - [x] Skip unused parameters followed by used variables in object/array spreads - [x] Re-assignments to array/object spreads do not respect `destructuredArrayIgnorePattern` (related to: https://github.com/oxc-project/oxc/issues/4435) - [x] #4493 - [x] References inside a nested scope are not considered usages (#4447) - [x] Port over typescript-eslint test cases _(wip, they've been copied and I'm slowly enabling them)_ - [x] Handle constructor properties ```ts class Foo { constructor(public a) {} // `a` should be allowed } ``` - [x] Read references in sequence expressions (that are not in the last position) should not count as a usage ```js let a = 0; let b = (a++, 0); console.log(b) ``` > Honestly, is anyone even writing code like this? - [x] function overload signatures should not be reported - [x] Named functions returned from other functions get incorrectly reported as unused (found by @camc314) ```js function foo() { return function bar() { } } Foo()() ``` - [x] false positive for TS modules within ambient modules ```ts declare global { // incorrectly marked as unused namespace jest { } } ``` ## Blockers - https://github.com/oxc-project/oxc/issues/4436 - https://github.com/oxc-project/oxc/issues/4437 - #4446 - #4447 - #4494 - #4495 ## Non-Blocking Issues - #4443 - #4475 (prevents checks on exported symbols from namespaces) |
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