[C++ PATCH] Only allow __label__ at the beginning of compound statements as documented (PR c++/32121)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

info gcc on __label__ says:

Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.

which is something the C frontend enforces, but C++ was not.
Fixed thusly, ok for trunk?

2007-09-27  Jakub Jelinek  <jakub@redhat.com>

	PR c++/32121
	* parser.c (cp_parser_compound_statement): Handle label-declarations
	at the beginning of the compound statement.
	(cp_parser_block_declaration): Issue diagnostics about __label__
	not at the beginning of a block.

	* g++.dg/ext/label4.C: Adjust error regexp.
	* g++.dg/ext/label6.C: Adjust error regexp.
	* g++.dg/ext/label7.C: New test.
	* g++.dg/ext/label8.C: New test.
	* g++.dg/ext/label9.C: New test.

--- gcc/cp/parser.c.jj	2007-09-14 11:54:32.000000000 +0200
+++ gcc/cp/parser.c	2007-09-27 15:56:24.000000000 +0200
@@ -6821,6 +6821,11 @@ cp_parser_expression_statement (cp_parse
    compound-statement:
      { statement-seq [opt] }
 
+   GNU extension:
+
+   compound-statement:
+     { label-declaration [opt] statement-seq [opt] }
+
    Returns a tree representing the statement.  */
 
 static tree
@@ -6834,6 +6839,9 @@ cp_parser_compound_statement (cp_parser 
     return error_mark_node;
   /* Begin the compound-statement.  */
   compound_stmt = begin_compound_stmt (in_try ? BCS_TRY_BLOCK : 0);
+  /* If the next keyword is `__label__' we have a label declaration.  */
+  while (cp_lexer_next_token_is_keyword (parser->lexer, RID_LABEL))
+    cp_parser_label_declaration (parser);
   /* Parse an (optional) statement-seq.  */
   cp_parser_statement_seq_opt (parser, in_statement_expr);
   /* Finish the compound-statement.  */
@@ -7711,7 +7719,6 @@ cp_parser_declaration (cp_parser* parser
 
    block-declaration:
      __extension__ block-declaration
-     label-declaration
 
    C++0x Extension:
 
@@ -7772,12 +7779,16 @@ cp_parser_block_declaration (cp_parser *
 	cp_parser_using_declaration (parser,
 				     /*access_declaration_p=*/false);
     }
-  /* If the next keyword is `__label__' we have a label declaration.  */
+  /* If the next keyword is `__label__' we have a misplaced label
+     declaration.  */
   else if (token1->keyword == RID_LABEL)
     {
-      if (statement_p)
-	cp_parser_commit_to_tentative_parse (parser);
-      cp_parser_label_declaration (parser);
+      cp_lexer_consume_token (parser->lexer);
+      error ("%<__label__%> not at the beginning of a block");
+      cp_parser_skip_to_end_of_statement (parser);
+      /* If the next token is now a `;', consume it.  */
+      if (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON))
+	cp_lexer_consume_token (parser->lexer);
     }
   /* If the next token is `static_assert' we have a static assertion.  */
   else if (token1->keyword == RID_STATIC_ASSERT)
--- gcc/testsuite/g++.dg/ext/label4.C.jj	2006-10-05 00:26:22.000000000 +0200
+++ gcc/testsuite/g++.dg/ext/label4.C	2007-09-27 15:50:01.000000000 +0200
@@ -3,4 +3,4 @@
 
 // { dg-do compile }
 
-__label__ *l;  // { dg-error "before" }
+__label__ *l;  // { dg-error "not at the beginning of" }
--- gcc/testsuite/g++.dg/ext/label6.C.jj	2007-08-13 15:09:39.000000000 +0200
+++ gcc/testsuite/g++.dg/ext/label6.C	2007-09-27 15:50:29.000000000 +0200
@@ -1,3 +1,3 @@
 // PR c++/32108
 
-__label__ L; // { dg-error "function scopes" }
+__label__ L; // { dg-error "not at the beginning" }
--- gcc/testsuite/g++.dg/ext/label7.C.jj	2007-09-27 15:50:50.000000000 +0200
+++ gcc/testsuite/g++.dg/ext/label7.C	2007-09-27 15:52:04.000000000 +0200
@@ -0,0 +1,12 @@
+// PR c++/32121
+// { dg-do compile }
+
+int f (void)
+{
+  a:;
+  __label__ a;	// { dg-error "not at the beginning" }
+  int b;
+  __label__ c;	// { dg-error "not at the beginning" }
+  a:;		// { dg-error "duplicate label" }
+  c:;
+}
--- gcc/testsuite/g++.dg/ext/label8.C.jj	2007-09-27 15:59:17.000000000 +0200
+++ gcc/testsuite/g++.dg/ext/label8.C	2007-09-27 15:58:06.000000000 +0200
@@ -0,0 +1,22 @@
+// PR c++/32121
+// { dg-do compile }
+
+int f (void)
+{
+  __label__ a, b;
+  __label__ c;
+  a:;
+  b:;
+  c:;
+  {
+    __label__ d;
+    d:;
+    if (0)
+      {
+	__label__ e;
+	__label__ f;
+	f:;
+	e:;
+      }
+  }
+}
--- gcc/testsuite/g++.dg/ext/label9.C.jj	2007-09-27 15:59:21.000000000 +0200
+++ gcc/testsuite/g++.dg/ext/label9.C	2007-09-27 15:59:11.000000000 +0200
@@ -0,0 +1,10 @@
+// PR c++/32121
+// { dg-do compile }
+
+int f (void)
+{
+  while (1)
+    __label__ a;	// { dg-error "not at the beginning" }
+  for (;;)
+    __label__ b;	// { dg-error "not at the beginning" }
+}

	Jakub