support for empty port connections

test/basic/unbound_port.sv

@@ -0,0 +1,29 @@
+`ifndef TRAIL
+`define TRAIL ,
+`endif
+
+module mod #(
+    parameter [23:0] KEY = "INV"
+) (a, b, c);
+    input wire [31:0] a, b, c;
+    initial #1 $display("%s a=%0d b=%0d c=%0d", KEY, a, b, c);
+endmodule
+
+module top;
+    mod #("MA0") MA0(, , );
+    mod #("MA1") MA1(1, , );
+    mod #("MA2") MA2(1, 2, );
+    mod #("MA3") MA3(1, 2, 3);
+    mod #("MA4") MA4(1, , 3);
+    mod #("MA5") MA5(1, , 3);
+    mod #("MA6") MA6(, 2, 3);
+    mod #("MA7") MA7(, , 3);
+    mod #("MB0") MB0(, , `TRAIL);
+    mod #("MB1") MB1(1, , `TRAIL);
+    mod #("MB2") MB2(1, 2, `TRAIL);
+    mod #("MB3") MB3(1, 2, 3 `TRAIL);
+    mod #("MB4") MB4(1, , 3 `TRAIL);
+    mod #("MB5") MB5(1, , 3 `TRAIL);
+    mod #("MB6") MB6(, 2, 3 `TRAIL);
+    mod #("MB7") MB7(, , 3 `TRAIL);
+endmodule

test/basic/unbound_port.v

@@ -0,0 +1,2 @@
+`define TRAIL
+`include "unbound_port.sv"