From acfcd78aec83512807718605faf698a20af26fdd Mon Sep 17 00:00:00 2001
From: Serge Pavlov <sepavloff@gmail.com>
Date: Thu, 6 Dec 2018 09:35:04 +0000
Subject: Diagnose friend function template redefinitions.

Friend function template defined in a class template becomes available if
the enclosing class template is instantiated. Until the function template
is used, it does not have a body, but still is considered a definition for
the purpose of redeclaration checks.

This change modifies redefinition check so that it can find the friend
function template definitions in instantiated classes.

Differential Revision: http://reviews.llvm.org/D21508

llvm-svn: 348473
---
 clang/lib/Sema/SemaDecl.cpp | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

(limited to 'clang/lib/Sema/SemaDecl.cpp')

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 083089fc994..a4545f2ff63 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -12737,6 +12737,29 @@ Sema::CheckForFunctionRedefinition(FunctionDecl *FD,
       }
     }
   }
+
+  if (!Definition)
+    // Similar to friend functions a friend function template may be a
+    // definition and do not have a body if it is instantiated in a class
+    // template.
+    if (FunctionTemplateDecl *FTD = FD->getDescribedFunctionTemplate()) {
+      for (auto I : FTD->redecls()) {
+        auto D = cast<FunctionTemplateDecl>(I);
+        if (D != FTD) {
+          assert(!D->isThisDeclarationADefinition() &&
+                 "More than one definition in redeclaration chain");
+          if (D->getFriendObjectKind() != Decl::FOK_None)
+            if (FunctionTemplateDecl *FT =
+                                       D->getInstantiatedFromMemberTemplate()) {
+              if (FT->isThisDeclarationADefinition()) {
+                Definition = D->getTemplatedDecl();
+                break;
+              }
+            }
+        }
+      }
+    }
+
   if (!Definition)
     return;
 
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