Re: [PATCH] c++: Accept C++11 attribute-definition [PR101582]

[Jason Merrill <jason@redhat.com>]

On 7/23/21 4:03 AM, Jakub Jelinek wrote:
> Hi!
> 
> As the following testcase shows, we don't parse properly
> C++11 attribute-declaration:
> https://eel.is/c++draft/dcl.dcl#nt:attribute-declaration
> 
> cp_parser_toplevel_declaration just handles empty-declaration parsing
> (with diagnostics for C++98)

This seems to be a bug: from the comments, 
cp_parser_toplevel_declaration is intended to only handle #pragma 
parsing, everything else should be in cp_parser_declaration.

As a result, we wrongly reject

extern "C" ;

So please move empty-declaration and attribute-declaration handling into 
cp_parser_declaration.

> and otherwise calls cp_parser_declaration
> which on it calls cp_parser_simple_declaration and rejects it with
> "does not declare anything" permerror.
> 
> The following patch instead handles it in cp_parser_toplevel_declaration
> by parsing the attributes (standard ones only, we've never supported
> __attribute__((...)); at namespace scope, so I'm not sure we need to
> introduce that), which for C++98 emits the needed diagnostics, and then
> warning if there are any attributes that we throw away on the floor.
> 
> I'll need this later for OpenMP directives at namespace scope, e.g.
> [[omp::directive (requires, atomic_default_mem_order(seq_cst))]];
> should be valid at namespace scope (and many other directives).
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> 2021-07-23  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/101582
> 	* parser.c (cp_parser_skip_std_attribute_spec_seq): Add a forward
> 	declaration.
> 	(cp_parser_toplevel_declaration): Parse attribute-declaration.
> 
> 	* g++.dg/cpp0x/gen-attrs-45.C: Expect a warning about ignored
> 	attributes instead of error.
> 	* g++.dg/cpp0x/gen-attrs-75.C: New test.
> 
> --- gcc/cp/parser.c.jj	2021-07-22 17:47:26.025761491 +0200
> +++ gcc/cp/parser.c	2021-07-22 19:09:28.487513184 +0200
> @@ -2507,6 +2507,8 @@ static tree cp_parser_std_attribute_spec
>     (cp_parser *);
>   static tree cp_parser_std_attribute_spec_seq
>     (cp_parser *);
> +static size_t cp_parser_skip_std_attribute_spec_seq
> +  (cp_parser *, size_t);
>   static size_t cp_parser_skip_attributes_opt
>     (cp_parser *, size_t);
>   static bool cp_parser_extension_opt
> @@ -14547,6 +14549,20 @@ cp_parser_toplevel_declaration (cp_parse
>         if (cxx_dialect < cxx11)
>   	pedwarn (input_location, OPT_Wpedantic, "extra %<;%>");
>       }
> +  else if (cp_lexer_nth_token_is (parser->lexer,
> +				  cp_parser_skip_std_attribute_spec_seq (parser,
> +									 1),
> +				  CPP_SEMICOLON))
> +    {
> +      location_t attrs_loc = token->location;
> +      tree std_attrs = cp_parser_std_attribute_spec_seq (parser);
> +      if (std_attrs != NULL_TREE)
> +	warning_at (make_location (attrs_loc, attrs_loc, parser->lexer),
> +		    OPT_Wattributes,
> +		    "attributes in attribute declaration are ignored");
> +      if (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON))
> +	cp_lexer_consume_token (parser->lexer);
> +    }
>     else
>       /* Parse the declaration itself.  */
>       cp_parser_declaration (parser, NULL_TREE);
> --- gcc/testsuite/g++.dg/cpp0x/gen-attrs-45.C.jj	2020-01-12 11:54:37.072403466 +0100
> +++ gcc/testsuite/g++.dg/cpp0x/gen-attrs-45.C	2021-07-22 19:14:38.250222344 +0200
> @@ -1,4 +1,4 @@
>   // PR c++/52906
>   // { dg-do compile { target c++11 } }
>   
> -[[gnu::deprecated]]; // { dg-error "does not declare anything" }
> +[[gnu::deprecated]]; // { dg-warning "attributes in attribute declaration are ignored" }
> --- gcc/testsuite/g++.dg/cpp0x/gen-attrs-75.C.jj	2021-07-22 19:14:58.438942693 +0200
> +++ gcc/testsuite/g++.dg/cpp0x/gen-attrs-75.C	2021-07-22 19:12:18.442158972 +0200
> @@ -0,0 +1,8 @@
> +// PR c++/101582
> +// { dg-do compile }
> +// { dg-options "" }
> +
> +;
> +[[]] [[]] [[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
> +[[foobar]];	// { dg-warning "attributes in attribute declaration are ignored" }
> +// { dg-warning "attributes only available with" "" { target c++98_only } .-1 }
> 
> 	Jakub
>