re PR c/67580 (Improve error message on missing "struct" tag)

	PR c/67580
	* c-decl.c (tag_exists_p): New function.
	* c-parser.c (c_parser_declaration_or_fndef): Give a hint when
	struct/union/enum keywords are missing.
	* c-tree.h (tag_exists_p): Declare.

	* gcc.dg/pr67580.c: New test.

From-SVN: r227803

gcc/c/ChangeLog

 2015-09-15  Marek Polacek  <polacek@redhat.com>
 
+	PR c/67580
+	* c-decl.c (tag_exists_p): New function.
+	* c-parser.c (c_parser_declaration_or_fndef): Give a hint when
+	struct/union/enum keywords are missing.
+	* c-tree.h (tag_exists_p): Declare.
+
+2015-09-15  Marek Polacek  <polacek@redhat.com>
+
 	* c-decl.c (lookup_label): Return NULL_TREE instead of 0.
 	(lookup_tag): Change the type of THISLEVEL_ONLY to bool.
 	Return NULL_TREE instead of 0.

gcc/c/c-decl.c

@@ -3856,6 +3856,18 @@ lookup_tag (enum tree_code code, tree name, bool thislevel_only,
   return b->decl;
 }
 
+/* Return true if a definition exists for NAME with code CODE.  */
+
+bool
+tag_exists_p (enum tree_code code, tree name)
+{
+  struct c_binding *b = I_TAG_BINDING (name);
+
+  if (b == NULL || b->decl == NULL_TREE)
+    return false;
+  return TREE_CODE (b->decl) == code;
+}
+
 /* Print an error message now
    for a recent invalid struct, union or enum cross reference.
    We don't print them immediately because they are not invalid

gcc/c/c-parser.c

@@ -1539,8 +1539,16 @@ c_parser_declaration_or_fndef (c_parser *parser, bool fndef_ok,
           || c_parser_peek_2nd_token (parser)->type == CPP_MULT)
       && (!nested || !lookup_name (c_parser_peek_token (parser)->value)))
     {
-      error_at (here, "unknown type name %qE",
-                c_parser_peek_token (parser)->value);
+      tree name = c_parser_peek_token (parser)->value;
+      error_at (here, "unknown type name %qE", name);
+      /* Give a hint to the user.  This is not C++ with its implicit
+	 typedef.  */
+      if (tag_exists_p (RECORD_TYPE, name))
+	inform (here, "use %<struct%> keyword to refer to the type");
+      else if (tag_exists_p (UNION_TYPE, name))
+	inform (here, "use %<union%> keyword to refer to the type");
+      else if (tag_exists_p (ENUMERAL_TYPE, name))
+	inform (here, "use %<enum%> keyword to refer to the type");
 
       /* Parse declspecs normally to get a correct pointer type, but avoid
          a further "fails to be a type name" error.  Refuse nested functions

gcc/c/c-tree.h

@@ -701,6 +701,7 @@ extern tree c_omp_reduction_lookup (tree, tree);
 extern tree c_check_omp_declare_reduction_r (tree *, int *, void *);
 extern void c_pushtag (location_t, tree, tree);
 extern void c_bind (location_t, tree, bool);
+extern bool tag_exists_p (enum tree_code, tree);
 
 /* In c-errors.c */
 extern void pedwarn_c90 (location_t, int opt, const char *, ...)

gcc/testsuite/ChangeLog

+2015-09-15  Marek Polacek  <polacek@redhat.com>
+
+	PR c/67580
+	* gcc.dg/pr67580.c: New test.
+
 2015-09-15  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/67470

gcc/testsuite/gcc.dg/pr67580.c

+/* PR c/67580 */
+/* { dg-do compile } */
+
+struct S { int s; };
+union U { int s; };
+enum E { A };
+
+void
+f (void)
+{
+  S s; /* { dg-error "unknown type name" } */
+/* { dg-message "use .struct. keyword to refer to the type" "" { target *-*-* } 11 } */
+  U u; /* { dg-error "unknown type name" } */
+/* { dg-message "use .union. keyword to refer to the type" "" { target *-*-* } 13 } */
+  E e; /* { dg-error "unknown type name" } */
+/* { dg-message "use .enum. keyword to refer to the type" "" { target *-*-* } 15 } */
+}
+
+void
+g (void)
+{
+  struct T { int i; };
+  union V { int i; };
+  enum F { J };
+  T t; /* { dg-error "unknown type name" } */
+/* { dg-message "use .struct. keyword to refer to the type" "" { target *-*-* } 25 } */
+  V v; /* { dg-error "unknown type name" } */
+/* { dg-message "use .union. keyword to refer to the type" "" { target *-*-* } 27 } */
+  F f; /* { dg-error "unknown type name" } */
+/* { dg-message "use .enum. keyword to refer to the type" "" { target *-*-* } 29 } */
+}