support quick info and go to definition on mapped keys

[Zzzen]

Fixes:

• Mapped keys do not preserve JSDoc documentation TypeScript#50715
• regression in "key remapping breaks definition navigation" TypeScript#56019
• [TypeScript] Mapped Types with Template Literal Keys Do Not Preserve Type Declaration References TypeScript#61094

This was originally implemented in microsoft/TypeScript#61061 (migrated here).

[Copilot]

Pull request overview

Adds language service support for Quick Info (hover) and Go to Definition on mapped type properties, including cases where keys are remapped (e.g. via as), aligning behavior with upstream TypeScript fixes for the linked issues.

Changes:

• Attach and surface JSDoc (notably @inheritDoc) on MappedTypeNode so hover can show documentation for remapped mapped properties.
• Improve go-to-definition for mapped properties by falling back to the mapped symbol’s syntheticOrigin declarations when the mapped property has no direct declarations.
• Add fourslash coverage + reference baselines for hover and go-to-definition on mapped keys.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
internal/parser/utilities.go	Includes KindMappedType in JSDoc comment range collection so mapped types can have lazily-parsed JSDoc in TS/TSX.
internal/parser/parser.go	Records preceding JSDoc info when parsing mapped types and attaches it via withJSDoc.
internal/checker/checker.go	Sets prop.Parent for mapped properties to the mapped type symbol to enable doc lookup via parent declarations.
internal/checker/services.go	Exposes GetMappedSyntheticOrigin helper for LS to navigate mapped symbols back to their source property symbol.
internal/ls/hover.go	Synthesizes hover documentation for mapped properties (when declaration is nil) using mapped type + synthetic origin declarations when @inheritDoc is present.
internal/ls/definition.go	Adds go-to-definition fallback to synthetic origin declarations for mapped properties with no declarations.
internal/fourslash/tests/quickInfoMappedType2_test.go	Adds/updates quick info fourslash coverage for mapped type @inheritDoc hover.
internal/fourslash/tests/quickInfoMappedType3_test.go	Adds hover baseline test for mapped type remapped keys showing inherited doc text.
internal/fourslash/tests/quickInfoMappedType4_test.go	Adds a quick info regression test for a different @inheritDoc placement scenario.
internal/fourslash/tests/goToDefinitionMappedType2_test.go	Adds go-to-definition fourslash test for mapped keys with remapping.
internal/fourslash/tests/goToDefinitionMappedType3_test.go	Adds go-to-definition fourslash test for mapped keys transformed with a suffix.
testdata/baselines/reference/fourslash/quickInfo/quickInfoMappedType3.baseline	New reference baseline for hover output on mapped properties.
testdata/baselines/reference/fourslash/goToDefinition/goToDefinitionMappedType2.baseline.jsonc	New reference baseline for go-to-definition on remapped mapped keys.
testdata/baselines/reference/fourslash/goToDefinition/goToDefinitionMappedType3.baseline.jsonc	New reference baseline for go-to-definition on suffix-transformed keys.

Comments suppressed due to low confidence (1)

internal/fourslash/tests/quickInfoMappedType3_test.go:54

• Same as above: this comment says hover docs are not displayed, but the updated baseline indicates documentation is shown. Please update the marker comment to match expected behavior.

// ❌ When hovering here, the documentation is NOT displayed.
me./*4*/getName();`

[Copilot]

The embedded test source still says hover documentation is not displayed for the mapped properties/call sites, but the baseline now shows documentation coming from the mapped type's @inheritdoc. Please update these ❌ comments to match the new expected behavior to avoid confusing future test readers.

This issue also appears on line 53 of the same file.

Suggested change

	// ❌ When hovering here, the documentation is NOT displayed.
	/*1*/getName: () => "Jake Carter",
	// ❌ When hovering here, the documentation is NOT displayed.
	/*2*/getAge: () => 35,
	// ❌ When hovering here, the documentation is NOT displayed.
	/*3*/getLocation: () => "United States",
	};
	// ❌ When hovering here, the documentation is NOT displayed.
	// ✅ When hovering here, the documentation is displayed, as it should.
	/*1*/getName: () => "Jake Carter",
	// ✅ When hovering here, the documentation is displayed, as it should.
	/*2*/getAge: () => 35,
	// ✅ When hovering here, the documentation is displayed, as it should.
	/*3*/getLocation: () => "United States",
	};
	// ✅ When hovering here, the documentation is displayed, as it should.

[DanielRosenwasser]

Actually we should not have comments because they were purely for the repo maintainers. Just drop these.

[Copilot]

This comment appears to be copy/pasted and doesn't match the test input (Y only has d, so the mapped type should produce getD). Consider correcting or removing it to keep the test self-explanatory.

Suggested change

	type T50 = Getters<Y>; // { getFoo: () => string, getBar: () => number }
	type T50 = Getters<Y>; // { getD: () => string }

[DanielRosenwasser]

Just remove the comments. They are lossy artifacts.

[Copilot]

This comment doesn't match the test input (Y only has d, so the resulting mapped property should be getD). Please correct or remove to avoid misleading documentation in the test case.

Suggested change

	type T50 = Getters<Y>; // { getFoo: () => string, getBar: () => number }
	type T50 = Getters<Y>; // { getD: () => string }

[Copilot]

The comment says documentation is "synthesized from" mapped type + syntheticOrigin declarations, but the implementation actually returns documentation from the first declaration in the combined list that produces non-empty output. Consider updating the comment (or changing the logic) so the behavior and documentation are consistent.

Suggested change

	// For mapped type symbols with @inheritDoc on the mapped type, synthesize documentation
	// from the mapped type's declarations and the syntheticOrigin's declarations.
	// For mapped type symbols with @inheritDoc on the mapped type, collect documentation
	// by considering the mapped type's declarations and the syntheticOrigin's declarations.

[Copilot]

hasJSDoc is a jsdocScannerInfo bitmask (not a boolean). Renaming it to something like jsdoc/jsdocInfo would better reflect its type and avoid confusion when reading the parser code.