glsl: empty declarations should be valid

Unlike C++, empty declarations such as

  float;

should be valid.  The spec is not explicit about this actually.

Some apps that generate their shader sources may rely on this.  This was
noted when porting one of them to Linux from Windows.

Reviewed-by: Chad Versace <chad@chad-versace.us>

Note: this is a candidate for the 7.11 branch.

src/glsl/ast_to_hir.cpp

@@ -2399,12 +2399,12 @@ ast_declarator_list::hir(exec_list *instructions,
 
    decl_type = this->type->specifier->glsl_type(& type_name, state);
    if (this->declarations.is_empty()) {
-      /* The only valid case where the declaration list can be empty is when
-       * the declaration is setting the default precision of a built-in type
-       * (e.g., 'precision highp vec4;').
-       */
-
       if (decl_type != NULL) {
+	 /* Warn if this empty declaration is not for declaring a structure.
+	  */
+	 if (this->type->specifier->structure == NULL) {
+	    _mesa_glsl_warning(&loc, state, "empty declaration");
+	 }
       } else {
 	    _mesa_glsl_error(& loc, state, "incomplete declaration");
       }

src/glsl/glsl_parser.yy

@@ -971,13 +971,9 @@ single_declaration:
 	fully_specified_type
 	{
 	   void *ctx = state;
-	   if ($1->specifier->type_specifier != ast_struct) {
-	      _mesa_glsl_error(& @1, state, "empty declaration list\n");
-	      YYERROR;
-	   } else {
-	      $$ = new(ctx) ast_declarator_list($1);
-	      $$->set_location(yylloc);
-	   }
+	   /* Empty declaration list is valid. */
+	   $$ = new(ctx) ast_declarator_list($1);
+	   $$->set_location(yylloc);
 	}
 	| fully_specified_type any_identifier
 	{