Revert "In MSVC compatibility mode, friend function declarations behave as function declarations" (#6143)

This reverts commit ad47114.

Temporary workaround for #6142

Reverting while there is a discussion at https://reviews.llvm.org/D124613
Will return back with the appropriate fix.

Author: Pavel Chupin

clang/lib/Sema/SemaDecl.cpp

@@ -9700,15 +9700,11 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     }
 
     if (isFriend) {
-      // In MSVC mode for older versions of the standard, friend function
-      // declarations behave as declarations
-      bool PerformFriendInjection =
-          getLangOpts().MSVCCompat && !getLangOpts().CPlusPlus20;
       if (FunctionTemplate) {
-        FunctionTemplate->setObjectOfFriendDecl(PerformFriendInjection);
+        FunctionTemplate->setObjectOfFriendDecl();
         FunctionTemplate->setAccess(AS_public);
       }
-      NewFD->setObjectOfFriendDecl(PerformFriendInjection);
+      NewFD->setObjectOfFriendDecl();
       NewFD->setAccess(AS_public);
     }
 

clang/test/SemaCXX/ms-friend-function-decl.cpp

@@ -2658,10 +2658,7 @@ TEST_P(ImportFriendFunctions, Lookup) {
       getTuDecl("struct X { friend void f(); };", Lang_CXX03, "input0.cc");
   auto *FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU, FunctionPattern);
   ASSERT_TRUE(FromD->isInIdentifierNamespace(Decl::IDNS_OrdinaryFriend));
-  // Before CXX20, MSVC treats friend function declarations as function
-  // declarations
-  ASSERT_EQ(FromTU->getLangOpts().MSVCCompat,
-            FromD->isInIdentifierNamespace(Decl::IDNS_Ordinary));
+  ASSERT_FALSE(FromD->isInIdentifierNamespace(Decl::IDNS_Ordinary));
   {
     auto FromName = FromD->getDeclName();
     auto *Class = FirstDeclMatcher<CXXRecordDecl>().match(FromTU, ClassPattern);
@@ -2705,10 +2702,7 @@ TEST_P(ImportFriendFunctions, LookupWithProtoAfter) {
   auto *FromNormal =
       LastDeclMatcher<FunctionDecl>().match(FromTU, FunctionPattern);
   ASSERT_TRUE(FromFriend->isInIdentifierNamespace(Decl::IDNS_OrdinaryFriend));
-  // Before CXX20, MSVC treats friend function declarations as function
-  // declarations
-  ASSERT_EQ(FromTU->getLangOpts().MSVCCompat,
-            FromFriend->isInIdentifierNamespace(Decl::IDNS_Ordinary));
+  ASSERT_FALSE(FromFriend->isInIdentifierNamespace(Decl::IDNS_Ordinary));
   ASSERT_FALSE(FromNormal->isInIdentifierNamespace(Decl::IDNS_OrdinaryFriend));
   ASSERT_TRUE(FromNormal->isInIdentifierNamespace(Decl::IDNS_Ordinary));
 
@@ -2799,10 +2793,7 @@ TEST_P(ImportFriendFunctions, ImportFriendChangesLookup) {
 
   ASSERT_TRUE(FromNormalF->isInIdentifierNamespace(Decl::IDNS_Ordinary));
   ASSERT_FALSE(FromNormalF->isInIdentifierNamespace(Decl::IDNS_OrdinaryFriend));
-  // Before CXX20, MSVC treats friend function declarations as function
-  // declarations
-  ASSERT_EQ(FromFriendTU->getLangOpts().MSVCCompat,
-            FromFriendF->isInIdentifierNamespace(Decl::IDNS_Ordinary));
+  ASSERT_FALSE(FromFriendF->isInIdentifierNamespace(Decl::IDNS_Ordinary));
   ASSERT_TRUE(FromFriendF->isInIdentifierNamespace(Decl::IDNS_OrdinaryFriend));
   auto LookupRes = FromNormalTU->noload_lookup(FromNormalName);
   ASSERT_TRUE(LookupRes.isSingleResult());