C++ PATCH to fix a part of c++/70513 (ICE-on-invalid with enums)

[Marek Polacek <polacek at redhat dot com>]

This is my attempt to fix at least a part of this PR.  I haven't been able to
come up with a fix that fixes the other part involving templates.

We were ICEing on code such as

struct S
{
  enum E : int;
  enum S::E : int { foo } e;
};

Clang rejects this with "extra qualification" error.  When I modified the test
to use structs rather than enums...

struct T
{
  struct U;
  struct T::U {};
};

...I found out that we reject this with "extra qualification not allowed".  So
I think the enum case is missing a similar check that this patch adds.

By the template part of this PR I mean that we ICE on

template <typename T>
class D
{
  enum D::A { foo } c;
};

where clang++ says
error: template specialization or definition requires a template parameter list
       corresponding to the nested type 'D<T>'
which I guess means that a valid code would have "<T>" after "D".  I thought
num_template_headers_for_class and cp_parser_check_template_parameters would
do the job here, but apparently something else needs to be used for this case.
But I'm at my wits' end here.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2016-04-08  Marek Polacek  <polacek@redhat.com>

	PR c++/70513
	* parser.c (cp_parser_enum_specifier): Check for extra qualification.

	* g++.dg/cpp0x/forw_enum12.C: New test.

diff --git gcc/cp/parser.c gcc/cp/parser.c
index 28e01af..dc0d1c8 100644
--- gcc/cp/parser.c
+++ gcc/cp/parser.c
@@ -17231,6 +17231,15 @@ cp_parser_enum_specifier (cp_parser* parser)
 			  type, prev_scope, nested_name_specifier);
 	      type = error_mark_node;
 	    }
+	  /* If that scope is the scope where the declaration is being placed
+	     the program is invalid.  */
+	  else if (nested_name_specifier == prev_scope)
+	    {
+	      permerror (type_start_token->location,
+			 "extra qualification not allowed");
+	      type = error_mark_node;
+	      nested_name_specifier = NULL_TREE;
+	    }
 	}
 
       if (scoped_enum_p)
diff --git gcc/testsuite/g++.dg/cpp0x/forw_enum12.C gcc/testsuite/g++.dg/cpp0x/forw_enum12.C
index e69de29..906ba68 100644
--- gcc/testsuite/g++.dg/cpp0x/forw_enum12.C
+++ gcc/testsuite/g++.dg/cpp0x/forw_enum12.C
@@ -0,0 +1,29 @@
+// PR c++/70513
+// { dg-do compile { target c++11 } }
+
+struct S1
+{
+  enum E : int;
+  enum S1::E : int { X } e; // { dg-error "extra qualification not allowed" }
+};
+
+struct S2
+{
+  enum class E : int;
+  enum class S2::E : int { X } e; // { dg-error "extra qualification not allowed" }
+};
+
+struct S3
+{
+  enum struct E : int;
+  enum struct S3::E : int { X } e; // { dg-error "extra qualification not allowed" }
+};
+
+struct S4
+{
+  struct S5
+  {
+    enum E : char;
+    enum S4::S5::E : char { X } e; // { dg-error "extra qualification not allowed" }
+  };
+};

	Marek