[gcc/devel/omp/gcc-11] c++: Accept C++11 attribute-definition [PR101582]

[gcc/devel/omp/gcc-11] c++: Accept C++11 attribute-definition [PR101582]

[Tobias Burnus]

https://gcc.gnu.org/g:3f57cbd4f23b0cf45ca5b048302e08e1e2b36f3e

commit 3f57cbd4f23b0cf45ca5b048302e08e1e2b36f3e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jul 30 10:53:56 2021 +0200

    c++: Accept C++11 attribute-definition [PR101582]
    
    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) 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 moves the handling of empty-declaration from
    cp_parser_toplevel_declaration to cp_parser_declaration and
    handles attribute-declaration in cp_parser_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).
    
    2021-07-30  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/101582
            * parser.c (cp_parser_skip_std_attribute_spec_seq): Add a forward
            declaration.
            (cp_parser_declaration): Parse empty-declaration and
            attribute-declaration.
            (cp_parser_toplevel_declaration): Don't parse empty-declaration here.
    
            * 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.
            * g++.dg/modules/pr101582-1.C: New test.
    
    (cherry picked from commit 77ab4e3be2d92b1ff671d58418d852195f10dd20)

Diff:
---
 gcc/cp/ChangeLog.omp                      | 12 +++++++++++
 gcc/cp/parser.c                           | 34 +++++++++++++++++++++++-------
 gcc/testsuite/ChangeLog.omp               | 11 ++++++++++
 gcc/testsuite/g++.dg/cpp0x/gen-attrs-45.C |  2 +-
 gcc/testsuite/g++.dg/cpp0x/gen-attrs-75.C | 35 +++++++++++++++++++++++++++++++
 gcc/testsuite/g++.dg/modules/pr101582-1.C |  9 ++++++++
 6 files changed, 94 insertions(+), 9 deletions(-)

diff --git a/gcc/cp/ChangeLog.omp b/gcc/cp/ChangeLog.omp
index 9db3e4f26e5..bdf818a78e6 100644
--- a/gcc/cp/ChangeLog.omp
+++ b/gcc/cp/ChangeLog.omp
@@ -1,3 +1,15 @@
+2021-07-30  Tobias Burnus  <tobias@codesourcery.com>
+
+	Backported from master:
+	2021-07-30  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/101582
+	* parser.c (cp_parser_skip_std_attribute_spec_seq): Add a forward
+	declaration.
+	(cp_parser_declaration): Parse empty-declaration and
+	attribute-declaration.
+	(cp_parser_toplevel_declaration): Don't parse empty-declaration here.
+
 2021-07-26  Tobias Burnus  <tobias@codesourcery.com>
 
 	Backported from master:
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 955677e15cb..8869a4884b7 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -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
@@ -14279,6 +14281,30 @@ cp_parser_declaration (cp_parser* parser, tree prefix_attrs)
   cp_token *token2 = (token1->type == CPP_EOF
 		      ? token1 : cp_lexer_peek_nth_token (parser->lexer, 2));
 
+  if (token1->type == CPP_SEMICOLON)
+    {
+      cp_lexer_consume_token (parser->lexer);
+      /* A declaration consisting of a single semicolon is invalid
+       * before C++11.  Allow it unless we're being pedantic.  */
+      if (cxx_dialect < cxx11)
+	pedwarn (input_location, OPT_Wpedantic, "extra %<;%>");
+      return;
+    }
+  else if (cp_lexer_nth_token_is (parser->lexer,
+				  cp_parser_skip_std_attribute_spec_seq (parser,
+									 1),
+				  CPP_SEMICOLON))
+    {
+      location_t attrs_loc = token1->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, "attribute ignored");
+      if (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON))
+	cp_lexer_consume_token (parser->lexer);
+      return;
+    }
+
   /* Get the high-water mark for the DECLARATOR_OBSTACK.  */
   void *p = obstack_alloc (&declarator_obstack, 0);
 
@@ -14429,14 +14455,6 @@ cp_parser_toplevel_declaration (cp_parser* parser)
        cp_parser_declaration.  (A #pragma at block scope is
        handled in cp_parser_statement.)  */
     cp_parser_pragma (parser, pragma_external, NULL);
-  else if (token->type == CPP_SEMICOLON)
-    {
-      cp_lexer_consume_token (parser->lexer);
-      /* A declaration consisting of a single semicolon is invalid
-       * before C++11.  Allow it unless we're being pedantic.  */
-      if (cxx_dialect < cxx11)
-	pedwarn (input_location, OPT_Wpedantic, "extra %<;%>");
-    }
   else
     /* Parse the declaration itself.  */
     cp_parser_declaration (parser, NULL_TREE);
diff --git a/gcc/testsuite/ChangeLog.omp b/gcc/testsuite/ChangeLog.omp
index b560a1b2f47..3e427ca7bc2 100644
--- a/gcc/testsuite/ChangeLog.omp
+++ b/gcc/testsuite/ChangeLog.omp
@@ -1,3 +1,14 @@
+2021-07-30  Tobias Burnus  <tobias@codesourcery.com>
+
+	Backported from master:
+	2021-07-30  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/101582
+	* 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.
+	* g++.dg/modules/pr101582-1.C: New test.
+
 2021-07-27  Tobias Burnus  <tobias@codesourcery.com>
 
 	Backported from master:
diff --git a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-45.C b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-45.C
index 573a1ab6cb0..2bdd549ea15 100644
--- a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-45.C
+++ b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-45.C
@@ -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 "attribute ignored" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-75.C b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-75.C
new file mode 100644
index 00000000000..bac80aa02ff
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-75.C
@@ -0,0 +1,35 @@
+// PR c++/101582
+// { dg-do compile }
+// { dg-options "" }
+
+;
+[[]] [[]] [[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+[[foobar]];	// { dg-warning "attribute ignored" }
+// { dg-warning "attributes only available with" "" { target c++98_only } .-1 }
+
+extern "C" ;
+extern "C" [[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+extern "C" extern "C" ;
+extern "C" extern "C" [[]][[]][[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+__extension__ ;
+__extension__ [[]];			// { dg-warning "attributes only available with" "" { target c++98_only } }
+__extension__ __extension__ ;
+__extension__ __extension__ [[]][[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+
+namespace N {
+
+;
+[[]] [[]] [[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+[[foobar]];	// { dg-warning "attribute ignored" }
+// { dg-warning "attributes only available with" "" { target c++98_only } .-1 }
+
+extern "C" ;
+extern "C" [[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+extern "C" extern "C" ;
+extern "C" extern "C" [[]][[]][[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+__extension__ ;
+__extension__ [[]];			// { dg-warning "attributes only available with" "" { target c++98_only } }
+__extension__ __extension__ ;
+__extension__ __extension__ [[]][[]];	// { dg-warning "attributes only available with" "" { target c++98_only } }
+
+}
diff --git a/gcc/testsuite/g++.dg/modules/pr101582-1.C b/gcc/testsuite/g++.dg/modules/pr101582-1.C
new file mode 100644
index 00000000000..1d3a3fcb6fa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/pr101582-1.C
@@ -0,0 +1,9 @@
+// PR c++/101582
+// { dg-additional-options "-fmodules-ts" }
+export module pr101582;
+// { dg-module-cmi "pr101582" }
+export ;			// { dg-error "export declaration does not declare anything" "" { xfail *-*-* } }
+export [[]];			// { dg-error "export declaration does not declare anything" "" { xfail *-*-* } }
+export				// { dg-error "export declaration does not declare anything" "" { xfail *-*-* } }
+{
+}