microsoft / microsoft/TypeScript
Behavior difference: Type emit inconsistency with dangling block comment in file
Open
@jakebailey is already working on this.
Since Jun 16, 2026.
Possible Improvement
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Description
Summary as below. I call this situation dangling block comment, since there are more than just newlines in between the block comments and the attached variables in the code.
Note that a fix for top, .ts will be a breaking change from TS 6.
| tsc | tsgo | |
|---|---|---|
| nonTop, .js | ✅ Dangling comment erased | ✅ Dangling comment erased |
| nonTop, .ts | ✅ Dangling comment erased | ✅ Dangling comment erased |
| top, .js | ✅ Dangling comment erased | ❌ Dangling comment attached to incorrect variable |
| top, .ts | ❌ Dangling comment attached to incorrect variable | ❌ Dangling comment attached to incorrect variable |
Steps to reproduce
- Start a plain new project
- "@typescript/native-preview": "7.0.0-dev.20260612.1",
- "typescript": "6.0.3"
- Run
npx tsgo --initto get the default tsconfig. Turn on these flags as well.- "allowJs": true,
- "checkJs": true,
- "stableTypeOrdering": true,
- "removeComments": false,
- Add the below files. Run
npx tsc&npx tsgoto see the difference.
/** ========> src/nonTopComment-js.js <======== */
export const e = 3;
/** Comment on nothing */
/** Comment on noop */
(function noop() {})();
export const pi = 3;
/** ========> src/nonTopComment-ts.ts <======== */
export const e = 3;
/** Comment on nothing */
/** Comment on noop */
(function noop() {})();
export const pi = 3;
/** ========> src/topComment-js.js <======== */
/** Comment on nothing */
/** Comment on noop */
(function noop() {})();
export const pi = 3;
/** ========> src/topComment-ts.ts <======== */
/** Comment on nothing */
/** Comment on noop */
(function noop() {})();
export const pi = 3;
Behavior with typescript@6.0
/** ========> dist/nonTopComment-js.d.ts <======== */
export const e: 3;
export const pi: 3;
//# sourceMappingURL=nonTopComment-js.d.ts.map
/** ========> dist/nonTopComment-ts.d.ts <======== */
export declare const e = 3;
export declare const pi = 3;
//# sourceMappingURL=nonTopComment-ts.d.ts.map
/** ========> dist/topComment-js.d.ts <======== */
export const pi: 3;
//# sourceMappingURL=topComment-js.d.ts.map
/** ========> dist/topComment-ts.d.ts <======== */
/** Comment on nothing */
export declare const pi = 3;
//# sourceMappingURL=topComment-ts.d.ts.map
Behavior with tsgo
/** ========> dist/nonTopComment-js.d.ts <======== */
export declare const e = 3;
export declare const pi = 3;
//# sourceMappingURL=nonTopComment-js.d.ts.map
/** ========> dist/nonTopComment-ts.d.ts <======== */
export declare const e = 3;
export declare const pi = 3;
//# sourceMappingURL=nonTopComment-ts.d.ts.map
/** ========> dist/topComment-js.d.ts <======== */
/** Comment on nothing */
export declare const pi = 3;
//# sourceMappingURL=topComment-js.d.ts.map
/** ========> dist/topComment-ts.d.ts <======== */
/** Comment on nothing */
export declare const pi = 3;
//# sourceMappingURL=topComment-ts.d.ts.map
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Assessment
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