[C++ Patch] PR 56871

[Paolo Carlini]

Hi,

seems an easy issue: we aren't allowing an explicit specializations 
differing from the template declaration with respect to the constexpr 
specifier.

Tested x86_64-linux.

Thanks,
Paolo.

//////////////////////
/cp
2013-04-08  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/56871
        * decl.c (validate_constexpr_redeclaration): Allow an explicit
        specialization to be different wrt the constexpr specifier.

/testsuite
2013-04-08  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/56871
        * g++.dg/cpp0x/constexpr-specialization.C: New.
Index: cp/decl.c
===================================================================
--- cp/decl.c   (revision 197572)
+++ cp/decl.c   (working copy)
@@ -1203,6 +1203,14 @@ validate_constexpr_redeclaration (tree old_decl, t
        = DECL_DECLARED_CONSTEXPR_P (new_decl);
       return true;
     }
+  /* 7.1.5 [dcl.constexpr]
+     Note: An explicit specialization can differ from the template
+     declaration with respect to the constexpr specifier.  */
+  if (TREE_CODE (old_decl) == FUNCTION_DECL
+      && TREE_CODE (new_decl) == FUNCTION_DECL
+      && ! DECL_TEMPLATE_SPECIALIZATION (old_decl)
+      && DECL_TEMPLATE_SPECIALIZATION (new_decl))
+    return true;
   error ("redeclaration %qD differs in %<constexpr%>", new_decl);
   error ("from previous declaration %q+D", old_decl);
   return false;
Index: testsuite/g++.dg/cpp0x/constexpr-specialization.C
===================================================================
--- testsuite/g++.dg/cpp0x/constexpr-specialization.C   (revision 0)
+++ testsuite/g++.dg/cpp0x/constexpr-specialization.C   (working copy)
@@ -0,0 +1,12 @@
+// PR c++/56871
+// { dg-options "-std=c++11" }
+
+template<typename T> constexpr int foo(T);
+template<> int foo(int);
+template<> int foo(int);            // { dg-error "previous" }
+template<> constexpr int foo(int);  // { dg-error "redeclaration" }
+
+template<typename T> int bar(T);
+template<> constexpr int bar(int);
+template<> constexpr int bar(int);  // { dg-error "previous" }
+template<> int bar(int);            // { dg-error "redeclaration" }