microsoft / microsoft/TypeScript

Behavior difference: Block comments on `@typedef` structural types are not preserved, if they are imported and reconstructed as inline types in another file

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#63,839 5 comments 0 reactions 0 assignees View on GitHub
Possible Improvement
Dominant language
Go
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Merged PRs (30d)
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Description

A follow-up on https://github.com/microsoft/typescript-go/issues/4235.

---

## Steps to reproduce

1. Start a plain new project
- "@typescript/native-preview": "7.0.0-dev.20260617.2",
- "typescript": "6.0.3"
2. Run `npx tsgo --init` to get the default tsconfig. Turn on these flags as well.
- "allowJs": true,
- "checkJs": true,
- "stableTypeOrdering": true,
3. Add the below files. Run `npx tsc` & `npx tsgo` to see the difference.

```ts
/** ========> src/lib.js <======== */
/**
* @typedef {Object} Foo
* @property {boolean} bool Whether `.bool` is true or not
*/
export class C {
/** @returns {Foo} */
getFoo() { return { bool: false }; }

/**
* @typedef {Object} Bar
* @property {boolean} bool Whether `.bool` is true or not
*/
/** @returns {Bar} */
getBar() { return { bool: false }; }
}

/** ========> src/mainJs.js <======== */
import { C } from './lib.js';

export class MainJs {
constructor() {
this.c = new C();
};

getFoo() { return { ...this.c.getFoo() }; }
getBar() { return { ...this.c.getBar() }; }
}

/** ========> src/mainTs.ts <======== */
import { C } from './lib.js';

export class MainTs {
constructor(public c: C) {};

getFoo() { return { ...this.c.getFoo() }; }
getBar() { return { ...this.c.getBar() }; }
}
```

## Behavior with `typescript@6.0`

```ts
/** ========> dist/mainJs.d.ts <======== */
export class MainJs {
c: C;
getFoo(): {
/**
* Whether `.bool` is true or not
*/
bool: boolean;
};
getBar(): {
/**
* Whether `.bool` is true or not
*/
bool: boolean;
};
}
import { C } from './lib.js';

/** ========> dist/mainTs.d.ts <======== */
import { C } from './lib.js';
export declare class MainTs {
c: C;
constructor(c: C);
getFoo(): {
/**
* Whether `.bool` is true or not
*/
bool: boolean;
};
getBar(): {
/**
* Whether `.bool` is true or not
*/
bool: boolean;
};
}
```

## Behavior with `tsgo`

```ts
/** ========> dist/mainJs.d.ts <======== */
import { C } from './lib.js';
export declare class MainJs {
c: C;
constructor();
getFoo(): {
bool: boolean;
};
getBar(): {
bool: boolean;
};
}

/** ========> dist/mainTs.d.ts <======== */
import { C } from './lib.js';
export declare class MainTs {
c: C;
constructor(c: C);
getFoo(): {
bool: boolean;
};
getBar(): {
bool: boolean;
};
}
```

Contributor guide

Open the contributing guide

Research direction

Reproduce the difference using src/lib.js, src/mainJs.js, and src/mainTs.ts with allowJs, checkJs, and stableTypeOrdering enabled, then run npx tsc and npx tsgo. Compare the generated dist/mainJs.d.ts and dist/mainTs.d.ts files; the fix is complete when reconstructed inline types preserve the @property comments in both outputs.

Written by the indexing model from the issue text.

Assessment

Tech stack
go, javascript, typescript
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
45/100

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