[ASTImporter][ASTImporterSpecificLookup] Add test for different operators

[martong]

Summary

This is to check that operators are handled properly in
ASTImporterSpecificLookup. Note, this lookup table is not used in LLDB, only
in CTU.

[a_sidorin]

LGTM!

unittests/AST/ASTImporterTest.cpp

4869

I think this comment should also be put before ASSERT_NE.

[martong]

• Add comment above ASSERT_NE

unittests/AST/ASTImporterTest.cpp

TEST_P(ASTImporterLookupTableTest, LookupFindsOverloadedNames) {
   auto *F2 = LastDeclMatcher<FunctionDecl>().match(ToTU, functionDecl());
   DeclarationName Name = F0->getDeclName();
   auto Res = LT.lookup(ToTU, Name);
   EXPECT_EQ(Res.size(), 3u);
   EXPECT_EQ(Res.count(F0), 1u);
   EXPECT_EQ(Res.count(F2), 1u);
 }
 
+TEST_P(ASTImporterLookupTableTest,
+       DifferentOperatorsShouldHaveDifferentResultSet) {
+  TranslationUnitDecl *ToTU = getToTuDecl(
+      R"(
+      struct X{};
+      void operator+(X, X);
+      void operator-(X, X);
+      )",
+      Lang_CXX);
+
+  ASTImporterLookupTable LT(*ToTU);
+  auto *FPlus = FirstDeclMatcher<FunctionDecl>().match(
+      ToTU, functionDecl(hasOverloadedOperatorName("+")));
+  auto *FMinus = FirstDeclMatcher<FunctionDecl>().match(
+      ToTU, functionDecl(hasOverloadedOperatorName("-")));
+  DeclarationName NamePlus = FPlus->getDeclName();
+  auto ResPlus = LT.lookup(ToTU, NamePlus);
+  EXPECT_EQ(ResPlus.size(), 1u);
+  EXPECT_EQ(ResPlus.count(FPlus), 1u);
+  EXPECT_EQ(ResPlus.count(FMinus), 0u);
+  DeclarationName NameMinus = FMinus->getDeclName();
+  auto ResMinus = LT.lookup(ToTU, NameMinus);
+  EXPECT_EQ(ResMinus.size(), 1u);
+  EXPECT_EQ(ResMinus.count(FMinus), 1u);
+  EXPECT_EQ(ResMinus.count(FPlus), 0u);
+  EXPECT_NE(*ResMinus.begin(), *ResPlus.begin());
+}
+
+TEST_P(ASTImporterLookupTableTest, LookupDeclNamesFromDifferentTUs) {
+  TranslationUnitDecl *ToTU = getToTuDecl(
+      R"(
+      struct X {};
+      void operator+(X, X);
+      )",
+      Lang_CXX);
+  auto *ToPlus = FirstDeclMatcher<FunctionDecl>().match(
+      ToTU, functionDecl(hasOverloadedOperatorName("+")));
+
+  Decl *FromTU = getTuDecl(
+      R"(
+      struct X {};
+      void operator+(X, X);
+      )",
+      Lang_CXX);
+  auto *FromPlus = FirstDeclMatcher<FunctionDecl>().match(
+      FromTU, functionDecl(hasOverloadedOperatorName("+")));
+
+  // FromPlus have a different TU, thus its DeclarationName is different too.
+  ASSERT_NE(ToPlus->getDeclName(), FromPlus->getDeclName());
+
+  ASTImporterLookupTable LT(*ToTU);
+  auto Res = LT.lookup(ToTU, ToPlus->getDeclName());
+  ASSERT_EQ(Res.size(), 1u);
+  EXPECT_EQ(*Res.begin(), ToPlus);
+
+  // FromPlus have a different TU, thus its DeclarationName is different too.
+  Res = LT.lookup(ToTU, FromPlus->getDeclName());
+  ASSERT_EQ(Res.size(), 0u);
+}
+
 static const RecordDecl * getRecordDeclOfFriend(FriendDecl *FD) {
   QualType Ty = FD->getFriendType()->getType();
   QualType NamedTy = cast<ElaboratedType>(Ty)->getNamedType();
   return cast<RecordType>(NamedTy)->getDecl();
 }
 
 TEST_P(ASTImporterLookupTableTest, LookupFindsFwdFriendClassDecl) {
   TranslationUnitDecl *ToTU = getToTuDecl(