C++ PATCH for c++/42687 (arg-dependent lookup regression)

[Jason Merrill]

When we fixed using explicit scope to suppress virtual calling, it broke 
using parentheses to suppress argument-dependent lookup.  Fixed thus.

Tested x86_64-pc-linux-gnu, applied to trunk, 4.4, 4.5 and 4.6.
commit 2bc3ed125eab1075ea18c7c80e5ab908130861fd
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue Apr 26 21:39:34 2011 -0400
        PR c++/42687
        * parser.c (cp_parser_primary_expression): Set *idk to
        CP_ID_KIND_NONE for a parenthesized identifier.

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 6da285e..68ce052 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -3437,6 +3437,12 @@ cp_parser_primary_expression (cp_parser *parser,
               `&A::B' might be a pointer-to-member, but `&(A::B)' is
               not.  */
            finish_parenthesized_expr (expr);
+           /* DR 705: Wrapping an unqualified name in parentheses
+              suppresses arg-dependent lookup.  We want to pass back
+              CP_ID_KIND_QUALIFIED for suppressing vtable lookup
+              (c++/37862), but none of the others.  */
+           if (*idk != CP_ID_KIND_QUALIFIED)
+             *idk = CP_ID_KIND_NONE;
          }
        /* The `>' token might be the end of a template-id or
           template-parameter-list now.  */
diff --git a/gcc/testsuite/g++.dg/lookup/koenig13.C 
b/gcc/testsuite/g++.dg/lookup/koenig13.C
new file mode 100644
index 0000000..625a181
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/koenig13.C
@@ -0,0 +1,16 @@
+// PR c++/42687
+// DR 705
+
+namespace N
+{
+    struct S { };
+    void f(const S &) { }
+}
+
+void f(const N::S &) { }
+
+int main()
+{
+    N::S v;
+    (f)(v); // no ambiguity: ADL is prevented with (), only ::f is considered
+}