#25292 made isolated declaration emit report a false TS9025 for a defaulted parameter whose annotation is an indexed access type. This breaks Vite's `UserConfig["base"]` case when Rolldown upgrades Oxc, even though the indexed property already includes `undefined`.
Oxc's isolated declaration emitter has no type checker, so it cannot safely resolve indexed accesses, type references, conditional types, or similar annotations. This change uses a syntax-only classification: widen or diagnose types whose syntax is conclusive, and preserve checker-dependent types rather than emit an unstable error. The union/intersection rules retain the distinct behavior of `any`, `never`, `unknown`, and `void`, and an explicit `undefined` union member is never duplicated.
Regression coverage includes the Rolldown/Vite case and a compact matrix of the relevant type algebra. The implementation and tests were reduced to one commit after review.
Validated with the isolated-declarations tests, strict Clippy, the all-features workspace suite, lint, docs, AST generation, and TypeScript 5.6.1-rc/6.0.3 type-algebra checks. The full local `just ready` run stopped only at a runner-dependent source-map snapshot because the repository expects Node 26.5.0 and this machine has 25.8.1; the remaining suite passed with that and the known terminal-color snapshot group skipped.
Follow-up to #25292. Related Rolldown failure: https://github.com/rolldown/rolldown/actions/runs/32158377691/job/95782148042?pr=10707
Disclosure: this change was prepared and verified with AI assistance (Codex).
## Summary
- emit `any | undefined` for default-initialized `any` parameters followed by required parameters
- add a regression fixture for #25290 and update the existing parameter snapshot
- preserve the existing handling of `unknown`
Closes#25290
## Summary
- report TS1016 while parsing formal parameter lists
- preserve initialized-parameter and rest-parameter behavior
- remove the equivalent semantic check and diagnostic
- update parser and semantic coverage snapshots
Follows #24596, which has now merged.
fixes#10948
This PR changes how comment options are interpreted.
`CodegenOptions::comments`, `CodegenOptions::annotation_comments` and
`CodegenOptions::legal_comments` are now independent of each other.
### `CodegenOptions::comments`
Controls printing of normal comments. At present, only some leading
comments are preserved. It does not control legal and annotation
comments.
### `CodegenOptions::annotation_comments`
Controls printing of annotation comments
* jsdoc: `/** jsdoc */`
* pure: `/* #__PURE__ */` and `/* #__NO_SIDE_EFFECTS__ */`
* webpack: `/* webpackChunkName */`
* vite: `/* @vite-ignore */`
* coverage: `v8 ignore`, `c8 ignore`, `node:coverage`, `istanbul ignore`
### `CodegenOptions::legal_comments`
Controls printing of legal comments
* starts with `//!` or `/*!`.
* contains `/* @license */` or `/* @preserve */`
---
Comment generation is also changed:
codegen first builds a comments map by keeping only the needed comments.
Printing functions will then print out comments in their respective
positions.
---
This PR reveals some incorrect comment interpretation:
* https://github.com/oxc-project/oxc/issues/10998
The default values in destructured parameters are retained in
declarations, which can cause captured variables to be part of the emit
when they shouldn't be. This can also lead to unnecessary isolated
declaration errors when those variables are themselves missing type
annotations and can't be inferred.
For example:
```ts
const x = 42;
const y = '';
export function fooGood3({a = x, b: [{c = y}]}: object): void {}
```
before this change will be emitted as:
```ts
declare const x = 42;
declare const y = '';
export declare function fooGood3({ a = x, b: [{ c = y }] }: object): void;
```
and after this change will be emitted as:
```ts
export declare function fooGood3({ a, b: [{ c }] }: object): void;
```
Co-authored-by: MichaelMitchell-at <=>
Dunqing