Previously `ScopeTree::get_child_ids` and `ScopeTree::get_child_ids_mut` returned an `Option`. Instead return the unwrapped value, in line with other methods e.g. `get_flags`.
> 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)
