[clang][Index] check TemplateTypeParmTypeLoc::getDecl() against nullptr in TypeIndexer and CursorVisitor

clang/lib/Index/IndexTypeSourceInfo.cpp

@@ -52,6 +52,9 @@ class TypeIndexer : public RecursiveASTVisitor<TypeIndexer> {
   bool VisitTemplateTypeParmTypeLoc(TemplateTypeParmTypeLoc TTPL) {
     SourceLocation Loc = TTPL.getNameLoc();
     TemplateTypeParmDecl *TTPD = TTPL.getDecl();
+    if (!TTPD)
+      return false;
+
     return IndexCtx.handleReference(TTPD, Loc, Parent, ParentDC,
                                     SymbolRoleSet());
   }

clang/test/Index/gh89389.cpp

@@ -0,0 +1,16 @@
+// RUN: c-index-test -test-load-source all %s -std=gnu++20 -fno-delayed-template-parsing
+
+namespace test18 {
+template<typename T>
+concept False = false;
+
+template <typename T> struct Foo { T t; };
+
+template<typename T> requires False<T>
+Foo(T) -> Foo<int>;
+
+template <typename U>
+using Bar = Foo<U>;
+
+Bar s = {1};
+} // namespace test18

clang/tools/libclang/CIndex.cpp

@@ -1693,12 +1693,16 @@ bool CursorVisitor::VisitTagTypeLoc(TagTypeLoc TL) {
 }
 
 bool CursorVisitor::VisitTemplateTypeParmTypeLoc(TemplateTypeParmTypeLoc TL) {
-  if (const auto *TC = TL.getDecl()->getTypeConstraint()) {
+  TemplateTypeParmDecl *D = TL.getDecl();
+  if (!D)
+    return true;
+
+  if (const auto *TC = D->getTypeConstraint()) {
     if (VisitTypeConstraint(*TC))
       return true;
   }
 
-  return Visit(MakeCursorTypeRef(TL.getDecl(), TL.getNameLoc(), TU));
+  return Visit(MakeCursorTypeRef(D, TL.getNameLoc(), TU));
 }
 
 bool CursorVisitor::VisitObjCInterfaceTypeLoc(ObjCInterfaceTypeLoc TL) {

clang/unittests/Index/IndexTests.cpp

@@ -453,6 +453,33 @@ TEST(IndexTest, ReadWriteRoles) {
                            WrittenAt(Position(6, 17))))));
 }
 
+TEST(IndexTest, gh89389) {
+  std::string Code = R"cpp(
+    namespace test18 {
+    template<typename T>
+    concept False = false;
+
+    template <typename T> struct Foo { T t; };
+
+    template<typename T> requires False<T>
+    Foo(T) -> Foo<int>;
+
+    template <typename U>
+    using Bar = Foo<U>;
+
+    Bar s = {1};
+    } // namespace test18
+  )cpp";
+  auto Index = std::make_shared<Indexer>();
+  IndexingOptions Opts;
+  Opts.IndexTemplateParameters = true;
+
+  // This test case is invalid code, so the expected return value is `false`.
+  // What is being tested is that there is no crash.
+  EXPECT_FALSE(tooling::runToolOnCodeWithArgs(
+      std::make_unique<IndexAction>(Index, Opts), Code, {"-std=c++20"}));
+}
+
 } // namespace
 } // namespace index
 } // namespace clang