[clang][ASTImporter][NFC] add unittests for unnamed EnumDecl (#100545)

These tests are for multiple anonymous EnumDecls structural eq test &
importing.

We found the anonymous enums importing issue a few days ago and tried to
fix it
but 0a6233a already did this. I think
these tests are still useful for regressions.

clang/unittests/AST/ASTImporterTest.cpp

@@ -9783,6 +9783,43 @@ TEST_P(ASTImporterOptionSpecificTestBase, ImportExistingEmptyAnonymousEnums) {
   EXPECT_EQ(ImportedE2, ToE1);
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase, ImportMultipleAnonymousEnumDecls) {
+  Decl *ToTU = getToTuDecl("", Lang_CXX03);
+  Decl *FromTU = getTuDecl(
+      R"(
+        struct foo {
+          enum { A };
+          enum { B };
+        };
+      )",
+      Lang_CXX03);
+
+  auto EnumConstA = enumConstantDecl(hasName("A"));
+  auto EnumConstB = enumConstantDecl(hasName("B"));
+
+  auto *FromA = FirstDeclMatcher<EnumConstantDecl>().match(FromTU, EnumConstA);
+  auto *FromB = FirstDeclMatcher<EnumConstantDecl>().match(FromTU, EnumConstB);
+
+  auto *ToA = Import(FromA, Lang_CXX03);
+  auto *ToB = Import(FromB, Lang_CXX03);
+
+  ASSERT_TRUE(ToA);
+  ASSERT_TRUE(ToB);
+
+  auto *ToFooA = FirstDeclMatcher<CXXRecordDecl>().match(
+      ToTU, tagDecl(has(enumDecl(has(EnumConstA)))));
+  auto *ToFooB = FirstDeclMatcher<CXXRecordDecl>().match(
+      ToTU, tagDecl(has(enumDecl(has(EnumConstB)))));
+  ASSERT_EQ(ToFooA, ToFooB);
+
+  // different EnumDecl
+  auto *ToEnumDeclA =
+      FirstDeclMatcher<EnumDecl>().match(ToTU, enumDecl(has(EnumConstA)));
+  auto *ToEnumDeclB =
+      FirstDeclMatcher<EnumDecl>().match(ToTU, enumDecl(has(EnumConstB)));
+  ASSERT_NE(ToEnumDeclA, ToEnumDeclB);
+}
+
 INSTANTIATE_TEST_SUITE_P(ParameterizedTests, ASTImporterLookupTableTest,
                          DefaultTestValuesForRunOptions);
 

clang/unittests/AST/StructuralEquivalenceTest.cpp

@@ -1109,6 +1109,20 @@ TEST_F(StructuralEquivalenceEnumTest, EnumsWithDifferentBody) {
   EXPECT_FALSE(testStructuralMatch(t));
 }
 
+TEST_F(StructuralEquivalenceEnumTest, AnonymousEnumsWithSameConsts) {
+  // field x is required to trigger comparison of the anonymous enum
+  auto t = makeNamedDecls("struct foo { enum { A } x; };",
+                          "struct foo { enum { A } x;};", Lang_CXX11);
+  EXPECT_TRUE(testStructuralMatch(t));
+}
+
+TEST_F(StructuralEquivalenceEnumTest, AnonymousEnumsWithDiffConsts) {
+  // field x is required to trigger comparison of the anonymous enum
+  auto t = makeNamedDecls("struct foo { enum { A } x; };",
+                          "struct foo { enum { B } x;};", Lang_CXX11);
+  EXPECT_FALSE(testStructuralMatch(t));
+}
+
 struct StructuralEquivalenceEnumConstantTest : StructuralEquivalenceTest {};
 
 TEST_F(StructuralEquivalenceEnumConstantTest, EnumConstantsWithSameValues) {