From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Wed, 19 Oct 2011 00:54:10 +0000 (+0000)
Subject: Add a -Wc++98-compat warning for friend functions of class templates which would
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=53e535161dfa9850de394b300915fc250eb0fdf4;p=clang

Add a -Wc++98-compat warning for friend functions of class templates which would
be implicitly instantiated (resulting in a redefinition) in C++98.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142468 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 5c4ecc8f9d..e5a49c658a 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2652,6 +2652,9 @@ def err_definition_of_explicitly_defaulted_member : Error<
 def err_redefinition_extern_inline : Error<
   "redefinition of a 'extern inline' function %0 is not supported in "
   "%select{C99 mode|C++}1">;
+def warn_cxx98_compat_friend_redefinition : Warning<
+  "friend function %0 would be implicitly redefined in C++98">,
+  InGroup<CXX98Compat>, DefaultIgnore;
 
 // This should eventually be an error.
 def warn_undefined_internal : Warning<
diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 02a05d5182..218beaa682 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -1230,16 +1230,33 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D,
 
     bool queuedInstantiation = false;
 
-    if (!SemaRef.getLangOptions().CPlusPlus0x &&
+    // C++98 [temp.friend]p5: When a function is defined in a friend function
+    //   declaration in a class template, the function is defined at each
+    //   instantiation of the class template. The function is defined even if it
+    //   is never used.
+    // C++11 [temp.friend]p4: When a function is defined in a friend function
+    //   declaration in a class template, the function is instantiated when the
+    //   function is odr-used.
+    //
+    // If -Wc++98-compat is enabled, we go through the motions of checking for a
+    // redefinition, but don't instantiate the function.
+    if ((!SemaRef.getLangOptions().CPlusPlus0x ||
+         SemaRef.Diags.getDiagnosticLevel(
+             diag::warn_cxx98_compat_friend_redefinition,
+             Function->getLocation())
+           != DiagnosticsEngine::Ignored) &&
         D->isThisDeclarationADefinition()) {
       // Check for a function body.
       const FunctionDecl *Definition = 0;
       if (Function->isDefined(Definition) &&
           Definition->getTemplateSpecializationKind() == TSK_Undeclared) {
-        SemaRef.Diag(Function->getLocation(), diag::err_redefinition)
-          << Function->getDeclName();
+        SemaRef.Diag(Function->getLocation(),
+                     SemaRef.getLangOptions().CPlusPlus0x ?
+                       diag::warn_cxx98_compat_friend_redefinition :
+                       diag::err_redefinition) << Function->getDeclName();
         SemaRef.Diag(Definition->getLocation(), diag::note_previous_definition);
-        Function->setInvalidDecl();
+        if (!SemaRef.getLangOptions().CPlusPlus0x)
+          Function->setInvalidDecl();
       }
       // Check for redefinitions due to other instantiations of this or
       // a similar friend function.
@@ -1250,7 +1267,8 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D,
           continue;
         switch (R->getFriendObjectKind()) {
         case Decl::FOK_None:
-          if (!queuedInstantiation && R->isUsed(false)) {
+          if (!SemaRef.getLangOptions().CPlusPlus0x &&
+              !queuedInstantiation && R->isUsed(false)) {
             if (MemberSpecializationInfo *MSInfo
                 = Function->getMemberSpecializationInfo()) {
               if (MSInfo->getPointOfInstantiation().isInvalid()) {
@@ -1267,10 +1285,14 @@ Decl *TemplateDeclInstantiator::VisitFunctionDecl(FunctionDecl *D,
           if (const FunctionDecl *RPattern
               = R->getTemplateInstantiationPattern())
             if (RPattern->isDefined(RPattern)) {
-              SemaRef.Diag(Function->getLocation(), diag::err_redefinition)
+              SemaRef.Diag(Function->getLocation(),
+                           SemaRef.getLangOptions().CPlusPlus0x ?
+                             diag::warn_cxx98_compat_friend_redefinition :
+                             diag::err_redefinition)
                 << Function->getDeclName();
               SemaRef.Diag(R->getLocation(), diag::note_previous_definition);
-              Function->setInvalidDecl();
+              if (!SemaRef.getLangOptions().CPlusPlus0x)
+                Function->setInvalidDecl();
               break;
             }
         }
diff --git a/test/SemaCXX/cxx98-compat.cpp b/test/SemaCXX/cxx98-compat.cpp
index 8da54f0da6..193a418d7f 100644
--- a/test/SemaCXX/cxx98-compat.cpp
+++ b/test/SemaCXX/cxx98-compat.cpp
@@ -179,3 +179,10 @@ template<typename T> typename T::ImPrivate SFINAEAccessControl(T t) { // expecte
 }
 int SFINAEAccessControl(...) { return 0; }
 int CheckSFINAEAccessControl = SFINAEAccessControl(PrivateMember());
+
+template<typename T>
+struct FriendRedefinition {
+  friend void Friend() {} // expected-warning {{friend function 'Friend' would be implicitly redefined in C++98}} expected-note {{previous}}
+};
+FriendRedefinition<int> FriendRedef1;
+FriendRedefinition<char> FriendRedef2; // expected-note {{requested here}}