Implement minimal getReferencedSymbolsForModule to fix crash

Implemented a minimal version of getReferencedSymbolsForModule that returns
module declarations as references. This, combined with the corrected condition
(checking for non-transient instead of transient), prevents the crash when
highlighting import paths.

The crash occurred because:
1. GetSymbolAtLocation on an import string returns a module symbol
2. getReferencedSymbolsForModuleIfDeclaredBySourceFile is called and now returns results
3. The old condition checked for transient symbols, causing non-transient module
   symbols to fall through to getReferencedSymbolsForSymbol
4. That function calls skipPastExportOrImportSpecifierOrUnion which panics on
   SourceFile declarations without parents

The fix ensures non-transient module symbols return early with the module references,
preventing the panic.

Added test TestDocumentHighlightImportPath that verifies document highlights work
on import paths and would hang/crash with the old condition.

Co-authored-by: jakebailey <[email protected]>

Author: Copilot

internal/fourslash/tests/documentHighlightImportPath_test.go

@@ -0,0 +1,21 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestDocumentHighlightImportPath(t *testing.T) {
+	t.Parallel()
+
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `// @Filename: /a.ts
+export const x = 0;
+
+// @Filename: /b.ts
+import { x } from "[|./a|]";`
+	f := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	f.VerifyBaselineDocumentHighlights(t, nil /*preferences*/, f.Ranges()[0])
+}

internal/ls/findallreferences.go

@@ -976,8 +976,44 @@ func getMergedAliasedSymbolOfNamespaceExportDeclaration(node *ast.Node, symbol *
 }
 
 func getReferencedSymbolsForModule(program *compiler.Program, symbol *ast.Symbol, excludeImportTypeOfExportEquals bool, sourceFiles []*ast.SourceFile, sourceFilesSet *collections.Set[string]) []*SymbolAndEntries {
-	// !!! not implemented
-	return nil
+	// Minimal implementation to prevent crashes when highlighting import paths.
+	// This returns module declarations as references, which allows the early return
+	// in getReferencedSymbolsForNode to work properly and avoid the panic in
+	// skipPastExportOrImportSpecifierOrUnion.
+
+	var references []*referenceEntry
+
+	// Add the module declarations themselves as references
+	if symbol.Declarations != nil {
+		for _, decl := range symbol.Declarations {
+			switch decl.Kind {
+			case ast.KindSourceFile:
+				// Don't include the source file itself
+			case ast.KindModuleDeclaration:
+				sourceFile := ast.GetSourceFileOfNode(decl)
+				if sourceFilesSet.Has(sourceFile.FileName()) {
+					references = append(references, &referenceEntry{
+						kind:     entryKindNode,
+						node:     decl.AsModuleDeclaration().Name(),
+						fileName: sourceFile.FileName(),
+					})
+				}
+			default:
+				// This may be merged with something
+				// TypeScript: Debug.assert(!!(symbol.flags & SymbolFlags.Transient))
+			}
+		}
+	}
+
+	// Return as SymbolAndEntries even if there are no references
+	// This ensures the condition check in getReferencedSymbolsForNode works properly
+	return []*SymbolAndEntries{{
+		definition: &Definition{
+			Kind:   definitionKindSymbol,
+			symbol: symbol,
+		},
+		references: references,
+	}}
 }
 
 func getReferenceAtPosition(sourceFile *ast.SourceFile, position int, program *compiler.Program) *refInfo {

testdata/baselines/reference/fourslash/documentHighlights/documentHighlightImportPath.baseline.jsonc

@@ -0,0 +1,3 @@
+// === documentHighlights ===
+// === /b.ts ===
+// import { x } from "/*HIGHLIGHTS*/./a";