[clang][ASTImport] fix issue on anonymous enum import (#93923)

Don't skip searching in `ToContext` during importing `EnumDecl`. And
`IsStructuralMatch` in `StructralEquivalence` can make sure to determine
whether the found result is match or not.

---------

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

Author: jcsxky

clang/lib/AST/ASTImporter.cpp

@@ -2929,7 +2929,7 @@ ExpectedDecl ASTNodeImporter::VisitEnumDecl(EnumDecl *D) {
 
   // We may already have an enum of the same name; try to find and match it.
   EnumDecl *PrevDecl = nullptr;
-  if (!DC->isFunctionOrMethod() && SearchName) {
+  if (!DC->isFunctionOrMethod()) {
     SmallVector<NamedDecl *, 4> ConflictingDecls;
     auto FoundDecls =
         Importer.findDeclsInToCtx(DC, SearchName);

clang/unittests/AST/ASTImporterTest.cpp

@@ -9674,6 +9674,46 @@ TEST_P(ASTImporterOptionSpecificTestBase, ImportInstantiatedFromMember) {
   EXPECT_TRUE(ImportedPartialSpecialization->getInstantiatedFromMember());
 }
 
+AST_MATCHER_P(EnumDecl, hasEnumConstName, StringRef, ConstName) {
+  for (EnumConstantDecl *D : Node.enumerators())
+    if (D->getName() == ConstName)
+      return true;
+  return false;
+}
+
+TEST_P(ASTImporterOptionSpecificTestBase, ImportAnonymousEnum) {
+  const char *ToCode =
+      R"(
+      struct A {
+        enum { E1, E2} x;
+        enum { E3, E4} y;
+      };
+      )";
+  Decl *ToTU = getToTuDecl(ToCode, Lang_CXX11);
+  auto *ToE1 = FirstDeclMatcher<EnumDecl>().match(
+      ToTU, enumDecl(hasEnumConstName("E1")));
+  auto *ToE3 = FirstDeclMatcher<EnumDecl>().match(
+      ToTU, enumDecl(hasEnumConstName("E3")));
+  const char *Code =
+      R"(
+      struct A {
+        enum { E1, E2} x;
+        enum { E3, E4} y;
+      };
+      )";
+  Decl *FromTU = getTuDecl(Code, Lang_CXX11);
+  auto *FromE1 = FirstDeclMatcher<EnumDecl>().match(
+      FromTU, enumDecl(hasEnumConstName("E1")));
+  auto *ImportedE1 = Import(FromE1, Lang_CXX11);
+  ASSERT_TRUE(ImportedE1);
+  EXPECT_EQ(ImportedE1, ToE1);
+  auto *FromE3 = FirstDeclMatcher<EnumDecl>().match(
+      FromTU, enumDecl(hasEnumConstName("E3")));
+  auto *ImportedE3 = Import(FromE3, Lang_CXX11);
+  ASSERT_TRUE(ImportedE3);
+  EXPECT_EQ(ImportedE3, ToE3);
+}
+
 INSTANTIATE_TEST_SUITE_P(ParameterizedTests, ASTImporterLookupTableTest,
                          DefaultTestValuesForRunOptions);