[gcc r12-8683] c++: pedwarn for empty unnamed enum in decl [PR67048]

[gcc r12-8683] c++: pedwarn for empty unnamed enum in decl [PR67048]

[Richard Biener]

https://gcc.gnu.org/g:60fed79c1e9a968eaedf292b298d19c9475ad37a

commit r12-8683-g60fed79c1e9a968eaedf292b298d19c9475ad37a
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Apr 28 16:50:06 2022 -0400

    c++: pedwarn for empty unnamed enum in decl [PR67048]
    
    [dcl.dcl]/5 says that
    
      enum { };
    
    is ill-formed, and since r197742 we issue a pedwarn.  However, the
    pedwarn also fires for
    
       enum { } x;
    
    which is well-formed.  So only warn when {} is followed by a ;.  This
    should be correct since you can't have "enum {}, <whatever>" -- that
    produces "expected unqualified-id before ',' token".
    
            PR c++/67048
    
    gcc/cp/ChangeLog:
    
            * parser.cc (cp_parser_enum_specifier): Warn about empty unnamed enum
            only when it's followed by a semicolon.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/enum42.C: New test.
    
    (cherry picked from commit fd0d3e9121c5aa65150d242676be6bbdc8d4a92a)

Diff:
---
 gcc/cp/parser.cc                    | 4 +++-
 gcc/testsuite/g++.dg/cpp0x/enum42.C | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 763df6f479b..5de1a80288e 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -21007,7 +21007,9 @@ cp_parser_enum_specifier (cp_parser* parser)
       /* If the next token is not '}', then there are some enumerators.  */
       else if (cp_lexer_next_token_is (parser->lexer, CPP_CLOSE_BRACE))
 	{
-	  if (is_unnamed && !scoped_enum_p)
+	  if (is_unnamed && !scoped_enum_p
+	      /* Don't warn for enum {} a; here.  */
+	      && cp_lexer_nth_token_is (parser->lexer, 2, CPP_SEMICOLON))
 	    pedwarn (type_start_token->location, OPT_Wpedantic,
 		     "ISO C++ forbids empty unnamed enum");
 	}
diff --git a/gcc/testsuite/g++.dg/cpp0x/enum42.C b/gcc/testsuite/g++.dg/cpp0x/enum42.C
new file mode 100644
index 00000000000..05b372a1947
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/enum42.C
@@ -0,0 +1,7 @@
+// PR c++/67048
+// { dg-do compile { target c++11 } }
+// { dg-options -Wpedantic }
+
+typedef enum {} X;
+enum {} x;
+enum {} y, z;