Handle nil queue as a was to delete a queue.

Treat this like assigning null to a dynamic array. This deletes the
queue and thus has the effect of clearing it.

PExpr.h

@@ -245,6 +245,10 @@ class PEConcat : public PExpr {
 
       virtual NetNet* elaborate_lnet(Design*des, NetScope*scope) const;
       virtual NetNet* elaborate_bi_net(Design*des, NetScope*scope) const;
+
+      virtual NetExpr*elaborate_expr(Design*des, NetScope*scope,
+				     ivl_type_t type, unsigned flags) const;
+
       virtual NetExpr*elaborate_expr(Design*des, NetScope*,
 				     unsigned expr_wid,
                                      unsigned flags) const;

elab_expr.cc

@@ -2497,6 +2497,24 @@ unsigned PEConcat::test_width(Design*des, NetScope*scope, width_mode_t&)
 // Keep track of the concatenation/repeat depth.
 static int concat_depth = 0;
 
+NetExpr* PEConcat::elaborate_expr(Design*, NetScope*,
+				  ivl_type_t type, unsigned /*flags*/) const
+{
+      switch (type->base_type()) {
+	  case IVL_VT_QUEUE:
+	    if (parms_.size() == 0) {
+		  NetENull*tmp = new NetENull;
+		  tmp->set_line(*this);
+		  return tmp;
+	    }
+	  default:
+	    cerr << get_fileline() << ": internal error: "
+		 << "I don't know how to elaborate(ivl_type_t)"
+		 << " this expression: " << *this << endl;
+	    return 0;
+      }
+}
+
 NetExpr* PEConcat::elaborate_expr(Design*des, NetScope*scope,
 				  unsigned expr_wid, unsigned flags) const
 {

parse.y

@@ -3456,11 +3456,14 @@ expr_primary
   | '{' '}'
       { // This is the empty queue syntax.
 	if (gn_system_verilog()) {
-	      yyerror(@1, "sorry: Expty queue expressions not supported.");
+	      list<PExpr*> empty_list;
+	      PEConcat*tmp = new PEConcat(empty_list);
+	      FILE_NAME(tmp, @1);
+	      $$ = tmp;
 	} else {
 	      yyerror(@1, "error: Concatenations are not allowed to be empty.");
+	      $$ = 0;
 	}
-	$$ = 0;
       }
 
   /* Cast expressions are primaries */

tgt-vvp/stmt_assign.c

@@ -976,6 +976,30 @@ static int show_stmt_assign_sig_darray(ivl_statement_t net)
       return errors;
 }
 
+static int show_stmt_assign_sig_queue(ivl_statement_t net)
+{
+      int errors = 0;
+      ivl_lval_t lval = ivl_stmt_lval(net, 0);
+      ivl_expr_t rval = ivl_stmt_rval(net);
+      ivl_signal_t var= ivl_lval_sig(lval);
+      ivl_type_t var_type= ivl_signal_net_type(var);
+      assert(ivl_type_base(var_type) == IVL_VT_QUEUE);
+
+      switch (ivl_expr_type(rval)) {
+	  case IVL_EX_NULL:
+	    errors += draw_eval_object(rval);
+	    break;
+	  default:
+	    fprintf(stderr, "XXXX: I don't know how to handle expr_type=%d here\n", ivl_expr_type(rval));
+	    fprintf(vvp_out, " ; XXXX expr_type=%d\n", ivl_expr_type(rval));
+	    errors += 1;
+	    break;
+      }
+
+      fprintf(vvp_out, "    %%store/obj v%p_0;\n", var);
+      return errors;
+}
+
 static int show_stmt_assign_sig_cobject(ivl_statement_t net)
 {
       int errors = 0;
@@ -1106,6 +1130,10 @@ int show_stmt_assign(ivl_statement_t net)
 	    return show_stmt_assign_sig_darray(net);
       }
 
+      if (sig && (ivl_signal_data_type(sig) == IVL_VT_QUEUE)) {
+	    return show_stmt_assign_sig_queue(net);
+      }
+
       if (sig && (ivl_signal_data_type(sig) == IVL_VT_CLASS)) {
 	    return show_stmt_assign_sig_cobject(net);
       }