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bug(semantic): typeof operator on type imports not counted as a reference #4494

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DonIsaac opened this issue Jul 26, 2024 · 1 comment · Fixed by #4500
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bug(semantic): typeof operator on type imports not counted as a reference #4494

DonIsaac opened this issue Jul 26, 2024 · 1 comment · Fixed by #4500
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A-semantic Area - Semantic C-bug Category - Bug good first issue Experience Level - Good for newcomers

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@DonIsaac
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DonIsaac commented Jul 26, 2024 •
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Part of #4445. Found by @camc314.

import type { mySchema } from './my-schema';
function test(arg: ReturnType<typeof mySchema>) {
  //                          ^^^^^^^^^^^^^^^ should be a `Type` reference
    arg;
}
test('');

Note that non-type imports work as expected:

import { mySchema } from './my-schema';
function test(arg: ReturnType<typeof mySchema>) {
    arg;
}
test('');

Screenshots

Incorrect:
image
Correct:
image
@DonIsaac DonIsaac added C-bug Category - Bug A-semantic Area - Semantic labels Jul 26, 2024
@DonIsaac DonIsaac mentioned this issue Jul 26, 2024
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@DonIsaac DonIsaac added the good first issue Experience Level - Good for newcomers label Jul 26, 2024
@Dunqing
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Dunqing commented Jul 27, 2024

This usage looks weird, but typescript supports it, and so must we.

@Dunqing Dunqing mentioned this issue Jul 27, 2024
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Dunqing pushed a commit that referenced this issue Jul 31, 2024
@DonIsaac
feat(linter): add eslint/no-unused-vars (⭐ attempt 3.2) (#4445)
b952942 
> 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: #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
- #4436
- #4437
- #4446
- #4447
- #4494
- #4495

## Non-Blocking Issues
- #4443
- #4475 (prevents checks on exported symbols from namespaces)
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fix(semantic): typeof operator cannot reference type-only import oxc-project/oxc
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