Preserve JSDoc @property comments when reconstructing typedef types

[veksa]

Fixes #4352

Problem

Block comments on @property entries of a @typedef were dropped when the structural type was reconstructed inline in another file. TypeScript 6 preserves them; tsgo did not.

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

// main.js
import { C } from './lib.js';
export class Main {
    constructor() { this.c = new C(); }
    getFoo() { return { ...this.c.getFoo() }; }
}

main.d.ts before (comment lost):

getFoo(): {
    bool: boolean;
};

main.d.ts after (matches tsc):

getFoo(): {
    /**
     * Whether `.bool` is true or not
     */
    bool: boolean;
};

Fix

The old JS .d.ts emitter copied comments onto synthesized property signatures via preserveCommentsOn / setSyntheticLeadingComments. The Go node builder used a raw setCommentRange in addPropertyToElementList, which drops comments for properties reparsed from @typedef/@property tags — their comment lives on a synthetic reparsed JSDoc rather than in a source comment range.

This reimplements preserveCommentsOn inside addPropertyToElementList: for a property whose declaration is a reparsed node carrying JSDoc, the comment text is reattached as a synthetic leading comment; otherwise the existing setCommentRange behavior is preserved. Only reparsed JS @property declarations take the new path, so TS declaration emit is unaffected.

Tests

Adds jsDeclarationsTypedefPropertyComments.ts covering both the same-file type alias and the cross-file inline reconstruction. Full local compiler suite and checker/transformer package tests pass.

AI usage disclosure

This change was authored with the assistance of an AI agent (Claude Code). I have read and understand the change and will discuss and revise it in review like any other contribution.

[veksa]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

Preserves JSDoc @property descriptions when typedef structures are synthesized into declaration types.

Changes:

• Reattaches reparsed JSDoc as synthetic leading comments.
• Adds a cross-file JavaScript declaration test and baselines.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/checker/nodebuilderimpl.go	Preserves comments on synthesized properties.
testdata/tests/cases/conformance/jsdoc/declarations/jsDeclarationsTypedefPropertyComments.ts	Adds regression coverage.
testdata/baselines/reference/conformance/jsDeclarationsTypedefPropertyComments.js	Verifies declaration output.
testdata/baselines/reference/conformance/jsDeclarationsTypedefPropertyComments.types	Records inferred types.
testdata/baselines/reference/conformance/jsDeclarationsTypedefPropertyComments.symbols	Records symbol bindings.