Fix hover JSDoc for mapped type properties

internal/fourslash/_scripts/failingTests.txt

@@ -327,7 +327,6 @@ TestQuickInfoJSDocFunctionThis
 TestQuickInfoJsDocGetterSetterNoCrash1
 TestQuickInfoJsdocTypedefMissingType
 TestQuickInfoJSExport
-TestQuickInfoMappedSpreadTypes
 TestQuickInfoMappedType
 TestQuickInfoMeaning
 TestQuickInfoModuleVariables
@@ -364,7 +363,6 @@ TestQuickInfoTypeOfThisInStatics
 TestQuickInfoTypeOnlyNamespaceAndClass
 TestQuickInfoUnionOfNamespaces
 TestQuickInfoUntypedModuleImport
-TestQuickinfoWrongComment
 TestRecursiveInternalModuleImport
 TestRegexDetection
 TestSelfReferencedExternalModule

internal/fourslash/tests/quickInfoMappedTypeJSDoc_test.go

@@ -0,0 +1,35 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestQuickInfoMappedTypeJSDoc(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+
+	// https://github.com/microsoft/typescript-go/issues/3659
+	const content = `
+type Test = {
+    /** a's comment */
+    a: string;
+};
+
+type Mapped = {
+    [K in keyof Test]: number;
+};
+
+const x: Mapped = {
+    a: 123
+};
+
+x./*1*/a
+`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+
+	f.VerifyQuickInfoAt(t, "1", "(property) a: number", "a's comment")
+}

internal/fourslash/tests/quickInfoRootSymbolJSDocAggregation_test.go

@@ -0,0 +1,55 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestQuickInfoRootSymbolJSDocAggregation(t *testing.T) {
+	t.Parallel()
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+
+	const content = `
+declare const distinct: {
+    /** first */
+    a: number;
+} & {
+    /** second */
+    a: number;
+};
+
+declare const duplicate: {
+    /** same */
+    a: number;
+} & {
+    /** same */
+    a: number;
+} & {
+    /** third */
+    a: number;
+};
+
+declare const mixed: {
+    /** first */
+    a: number;
+} & {
+    /** second */
+    a: number;
+} & {
+    /** first */
+    a: number;
+};
+
+distinct./*distinct*/a
+duplicate./*duplicate*/a
+mixed./*mixed*/a
+`
+	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	defer done()
+
+	f.VerifyQuickInfoAt(t, "distinct", "(property) a: number", "first\nsecond")
+	f.VerifyQuickInfoAt(t, "duplicate", "(property) a: number", "same\nthird")
+	f.VerifyQuickInfoAt(t, "mixed", "(property) a: number", "first\nsecond")
+}

internal/ls/hover.go

@@ -98,6 +98,11 @@ func (l *LanguageService) getQuickInfoAndDocumentationForSymbol(c *checker.Check
 		return quickInfo, documentation
 	}
 
+	documentation = l.documentationFromRootSymbols(c, symbol, node, contentFormat)
+	if documentation != "" {
+		return quickInfo, documentation
+	}
+
 	return quickInfo, l.documentationFromAlias(c, symbol, node, contentFormat)
 }
 
@@ -148,6 +153,44 @@ func (l *LanguageService) documentationFromAlias(c *checker.Checker, symbol *ast
 	return ""
 }
 
+func (l *LanguageService) documentationFromRootSymbols(c *checker.Checker, symbol *ast.Symbol, node *ast.Node, contentFormat lsproto.MarkupKind) string {
+	if symbol == nil {
+		return ""
+	}
+
+	var docs []string
+	for _, rootSymbol := range c.GetRootSymbols(symbol) {
+		if rootSymbol == nil {
+			continue
+		}
+		declaration := rootSymbol.ValueDeclaration
+		if declaration == nil {
+			declaration = core.FirstOrNil(rootSymbol.Declarations)
+		}
+		if declaration == nil {
+			continue
+		}
+		if documentation := l.getDocumentationFromDeclaration(c, rootSymbol, declaration, node, contentFormat, false /*commentOnly*/); documentation != "" {
+			docs = core.AppendIfUnique(docs, documentation)
+		}
+	}
+
+	if len(docs) == 0 {
+		return ""
+	}
+	if len(docs) == 1 {
+		return docs[0]
+	}
+
+	var b strings.Builder
+	b.WriteString(docs[0])
+	for _, doc := range docs[1:] {
+		b.WriteString("\n")
+		b.WriteString(doc)
+	}
+	return b.String()
+}
+
 func (l *LanguageService) getDocumentationFromDeclaration(c *checker.Checker, symbol *ast.Symbol, declaration *ast.Node, location *ast.Node, contentFormat lsproto.MarkupKind, commentOnly bool) string {
 	if declaration == nil {
 		return ""

testdata/baselines/reference/fourslash/quickInfo/quickInfoOnUnionPropertiesWithIdenticalJSDocComments01.baseline

@@ -30,7 +30,7 @@
 // | ```typescript
 // | (property) language?: string | undefined
 // | ```
-// | 
+// | A language id, like `typescript`.
 // | ----------------------------------------------------------------------
 [
   {
@@ -46,7 +46,7 @@
     "item": {
       "contents": {
         "kind": "markdown",
-        "value": "```typescript\n(property) language?: string | undefined\n```\n"
+        "value": "```typescript\n(property) language?: string | undefined\n```\nA language id, like `typescript`."
       },
       "range": {
         "start": {