Support non-overridable parameters in classes

SystemVerilog allows `parameter` and `localparam` to declare constants
within a class scope.  E.g.

```SystemVerilog
class C;
localparam A = 10;
endclass
```

In this context both declare a local parameter that can not be overwritten.

Supporting this can be achieved for the most part by adding a parser
sub-rule in class declaration rule. In addition some extra support code is
needed to mark the parameter as non-overridable.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

elab_scope.cc

@@ -524,6 +524,8 @@ static void elaborate_scope_class(Design*des, NetScope*scope, PClass*pclass)
 
       class_scope->add_typedefs(&pclass->typedefs);
 
+      collect_scope_parameters(des, class_scope, pclass->parameters);
+
 	// Elaborate enum types declared in the class. We need these
 	// now because enumeration constants can be used during scope
 	// elaboration.

parse.y

@@ -978,6 +978,8 @@ class_item /* IEEE1800-2005: A.1.8 */
 	yyerrok;
       }
 
+  | parameter_declaration
+
   | error ';'
       { yyerror(@2, "error: invalid class item.");
 	yyerrok;
@@ -2016,7 +2018,7 @@ package_import_item_list
 
 package_item /* IEEE1800-2005 A.1.10 */
   : timeunits_declaration
-  | parameter_or_localparam param_type parameter_assign_list ';'
+  | parameter_declaration
   | type_declaration
   | function_declaration
   | task_declaration
@@ -2697,7 +2699,7 @@ block_item_decl
       { if ($2) pform_make_events($2, @1.text, @1.first_line);
       }
 
-  | parameter_or_localparam param_type parameter_assign_list ';'
+  | parameter_declaration
 
   /* Blocks can have type declarations. */
 
@@ -5570,6 +5572,9 @@ param_type : data_type_or_implicit { param_data_type = $1; }
 parameter : K_parameter { param_is_local = false; };
 localparam : K_localparam { param_is_local = true; };
 
+parameter_declaration
+  : parameter_or_localparam param_type parameter_assign_list ';'
+
 parameter_or_localparam
   : parameter
   | localparam

pform.cc

@@ -3213,6 +3213,9 @@ void pform_set_parameter(const struct vlltype&loc,
           scope->has_parameter_port_list)
 	    overridable = false;
 
+      if (pform_in_class())
+	    overridable = false;
+
       Module::param_expr_t*parm = new Module::param_expr_t();
       FILE_NAME(parm, loc);
 

pform.h

@@ -202,6 +202,7 @@ extern void pform_set_this_class(const struct vlltype&loc, PTaskFunc*net);
 extern void pform_set_constructor_return(PFunction*net);
 
 extern void pform_end_class_declaration(const struct vlltype&loc);
+extern bool pform_in_class();
 
 extern void pform_make_udp(perm_string name, std::list<perm_string>*parms,
 			   std::vector<PWire*>*decl, std::list<std::string>*table,

pform_pclass.cc

@@ -164,3 +164,8 @@ void pform_end_class_declaration(const struct vlltype&loc)
       pform_cur_class = 0;
       pform_pop_scope();
 }
+
+bool pform_in_class()
+{
+      return pform_cur_class != 0;
+}