Show the JSDoc written on an import x = a.x alias in hover and completions

[patrick kettner (patrickkettner)]

Fixes #64655

Analysis

declare namespace a {
  /** on the declaration */
  export function f(): void;
}
declare namespace b {
  /** on the alias */
  export import f = a.f;
}
b.f; // 6.0 hovers "on the alias", 7.x "on the declaration"

getDocumentationForSymbol never looks at the alias's own declaration. The declaration it receives is the target's, recorded while the display walk resolves the alias, and documentationFromAlias resolves to the target again. The parser does attach the comment to the import f = a.f node, it is just never read. Completion details go through the same function, so the completion entry shows the same thing.

Fix

documentationFromAliasDeclaration reads the alias's own JSDoc, and getDocumentationForSymbol tries it right after the call-signature documentation. At a call site the recorded declaration is the resolved signature's and keeps priority, so hover on b.f() still shows the declaration's comment. This matches 6.0's symbolDisplay.

I tried letting documentationFromSignature return docs for any resolved-signature declaration first. That moved quickInfoCommentsFunctionExpression away from what 6.0 shows, so I dropped it.

quickInfoOnInternalAliases now gets its documentation right but stays skipped, since its display text still differs from 6.0.

Copilot Checklist

I successfully ran the applicable command at the end of my session, and it completed without error:

• npx hereby validate
• npx hereby validate --api (for TypeScript API changes)

I used Claude Code to write the patch and the test, and I have read and reviewed both.

[Copilot]

Copilot review overview

🟡 Changes recommended

Merged alias symbols may read JSDoc from a non-alias declaration.

Review effort: Balanced
Findings: 1

Open (1)

• Select the actual alias declaration instead of Declarations[0] · New

What changed in this PR

Restores alias-authored JSDoc in hover and completion details.

Changes:

• Adds alias declaration documentation lookup with call-site precedence.
• Adds fourslash coverage and hover baseline.

File	Description
tsc/​internal/​ls/​hover.go	Resolves documentation from alias declarations.
tsc/​internal/​fourslash/​tests/​hoverImportEqualsAliasJSDoc_test.go	Tests hover and completions.
tsc/​testdata/​baselines/​reference/​fourslash/​quickInfo/​hoverImportEqualsAliasJSDoc.baseline	Records expected hover output.

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[patrick kettner (patrickkettner)]

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