Re: [patch] fix PR c++/14136: Duplicate error message

[Volker Reichelt <reichelt at igpm dot rwth-aachen dot de>]

On  2 Dec, Giovanni Bajo wrote:
> Volker Reichelt <reichelt@igpm.rwth-aachen.de> wrote:
> 
>> For the following code snippet we issue a duplicate diagnostic on
> mainline:
>>
>> ==========================
>> struct A
>> {
>>     typedef A B;
>>     ~B();
>> };
>> ==========================
>>
>> PR14136.cc:4: error: typedef-name 'A::B' used as destructor declarator
>> PR14136.cc:4: error: typedef-name 'A::B' used as destructor declarator
>>
>> This is because we issue the error when we are parsing the declaration
>> tentatively and then again when we parse it for real.
>>
>> The following patch fixes that by not issuing the error message when we
>> do tentative parsing only.
> 
> I don't recall us doing a check like this to avoid error messages anywhere
> else in the parser. Usually, we use cp_parser_error: in tentative parsing,
> it does not emit the error message but marks the parsing attempt as failed;
> in non-tenative parsing, it emits a normal error message.
> 
> So I am not sure this is the correct way to go.

Good point.

Alas, cp_parser_error can only deal with a simple string, and not with
"%qD" which is used to output the typedef-name. In cp_parser_lookup_name
occured a similar problem. It is dealt with in the following way:

  /* The error message we have to print is too complicated for
     cp_parser_error, so we incorporate its actions directly.  */
  if (!cp_parser_simulate_error (parser))
    {
      error ("reference to %qD is ambiguous", name);
      print_candidates (decl);
    }

In fact, cp_parser_simulate_error in fact calls
!cp_parser_committed_to_tentative_parse, but does some additional
stuff (like marking the attempt as failed), too.
So here's an updated version which uses cp_parser_simulate_error
instead of just cp_parser_committed_to_tentative_parse.

OK to apply to mainline once this passes bootstrap and regtesting?

Regards,
Volker

2004-12-02  Volker Reichelt  <reichelt@igpm.rwth-aachen.de>

	PR c++/14136
	* parser.c (cp_parser_unqualified_id): Do not issue error message
	for typedef-name as destructor declarator when parsing tentatively.

Index: parser.c
===================================================================
RCS file: /usr/local/gcc/CVS/gcc-cvs/gcc/gcc/cp/parser.c,v
retrieving revision 1.276
diff -u -p -r1.276 parser.c
--- parser.c	3 Nov 2004 02:48:37 -0000	1.276
+++ parser.c	27 Nov 2004 07:07:14 -0000
@@ -3234,7 +3234,8 @@ cp_parser_unqualified_id (cp_parser* par
 	   identifier in the declarator for a destructor declaration.  */
 	if (declarator_p
 	    && !DECL_IMPLICIT_TYPEDEF_P (type_decl)
-	    && !DECL_SELF_REFERENCE_P (type_decl))
+	    && !DECL_SELF_REFERENCE_P (type_decl)
+	    && !cp_parser_simulate_error (parser))
 	  error ("typedef-name %qD used as destructor declarator",
 		 type_decl);
 
===================================================================