[clang][ASTImporter] import InstantiatedFromMember of ClassTemplateSpecializationDecl (#76493)

import of `ClassTemplateSpecializationDecl` didn't set
`InstantiatedFromMember` and this makes ast-dump crash. import and set
`InstantiatedFromMember`. fix
[issue](#76469)

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

Author: jcsxky

clang/lib/AST/ASTImporter.cpp

@@ -6141,6 +6141,11 @@ ExpectedDecl ASTNodeImporter::VisitClassTemplateSpecializationDecl(
                                                   InsertPos))
       // Add this partial specialization to the class template.
       ClassTemplate->AddPartialSpecialization(PartSpec2, InsertPos);
+    if (Expected<ClassTemplatePartialSpecializationDecl *> ToInstOrErr =
+            import(PartialSpec->getInstantiatedFromMember()))
+      PartSpec2->setInstantiatedFromMember(*ToInstOrErr);
+    else
+      return ToInstOrErr.takeError();
 
     updateLookupTableForTemplateParameters(*ToTPList);
   } else { // Not a partial specialization.

clang/unittests/AST/ASTImporterTest.cpp

@@ -9342,6 +9342,39 @@ TEST_P(ASTImporterOptionSpecificTestBase, ImportConflictTypeAliasTemplate) {
   EXPECT_FALSE(ImportedCallable);
 }
 
+AST_MATCHER(ClassTemplateSpecializationDecl, hasInstantiatedFromMember) {
+  if (auto Instantiate = Node.getInstantiatedFrom()) {
+    if (auto *FromPartialSpecialization =
+            Instantiate.get<ClassTemplatePartialSpecializationDecl *>()) {
+      return nullptr != FromPartialSpecialization->getInstantiatedFromMember();
+    }
+  }
+  return false;
+}
+
+TEST_P(ASTImporterOptionSpecificTestBase, ImportInstantiatedFromMember) {
+  const char *Code =
+      R"(
+      template <typename> struct B {
+        template <typename, bool = false> union D;
+        template <typename T> union D<T> {};
+        D<int> d;
+      };
+      B<int> b;
+      )";
+  Decl *FromTU = getTuDecl(Code, Lang_CXX11);
+  auto *FromD = FirstDeclMatcher<ClassTemplateSpecializationDecl>().match(
+      FromTU, classTemplateSpecializationDecl(hasName("D"),
+                                              hasInstantiatedFromMember()));
+  auto *FromPartialSpecialization =
+      cast<ClassTemplatePartialSpecializationDecl *>(
+          FromD->getInstantiatedFrom());
+  ASSERT_TRUE(FromPartialSpecialization->getInstantiatedFromMember());
+  auto *ImportedPartialSpecialization =
+      Import(FromPartialSpecialization, Lang_CXX11);
+  EXPECT_TRUE(ImportedPartialSpecialization->getInstantiatedFromMember());
+}
+
 INSTANTIATE_TEST_SUITE_P(ParameterizedTests, ASTImporterLookupTableTest,
                          DefaultTestValuesForRunOptions);