[PATCH] Implement DR136

[Richard Smith]

On Tue, Jun 25, 2013 at 12:59 AM, David Majnemer
<david.majnemer at gmail.com> wrote:
> The attached patch implements DR136 [*], "Default arguments and friend
> functions."
>
> The crux of this issue is that a function declaration that specifies a
> default argument must define the function and be it's only declaration.
>
> [*] http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#136

--- lib/Sema/SemaDeclCXX.cpp	(revision 184825)
+++ lib/Sema/SemaDeclCXX.cpp	(working copy)
@@ -404,6 +404,15 @@
   }
 }

+static bool functionDeclHasDefaultArgument(const FunctionDecl *FD) {
+  for (unsigned NumParams = FD->getNumParams(); NumParams > 0; --NumParams) {
+    const ParmVarDecl *PVD = FD->getParamDecl(NumParams-1);
+    if (PVD->hasDefaultArg() && !PVD->hasInheritedDefaultArg())
+      return true;
+  }

You can bail out early if you hit a parameter that doesn't have a
default argument (since no earlier parameters can have a default
argument).


@@ -578,6 +587,18 @@
     Invalid = true;
   }

+  // C++11 [dcl.fct.default]p4: If a friend declaration specifies a default
+  // argument expression, that declaration shall be a definition and shall be
+  // the only declaration of the function or function template in the
+  // translation unit.
+  if (!isa<CXXMethodDecl>(Old) &&

What is this check for?


+      Old->getFriendObjectKind() == Decl::FOK_Undeclared &&
+      functionDeclHasDefaultArgument(Old)) {
+      Diag(New->getLocation(), diag::err_friend_decl_with_def_arg_redeclared);
+      Diag(Old->getLocation(), diag::note_previous_declaration);
+      Invalid = true;
+    }

Too much indentation for these 4 lines.


@@ -11377,6 +11398,18 @@
     else
       FD = cast<FunctionDecl>(ND);

+    // C++11 [dcl.fct.default]p4: If a friend declaration specifies a
+    // default argument expression, that declaration shall be a definition
+    // and shall be the only declaration of the function or function
+    // template in the translation unit.
+    if (!isa<CXXMethodDecl>(FD) && functionDeclHasDefaultArgument(FD)) {

This isa check looks suspicious. Doesn't it lead to us incorrectly
accepting this:

  struct A { void f(int); };
  struct B { friend void A::f(int = 0); };

?