Add support for null ports (#2875)

bin/verilator

@@ -4729,6 +4729,17 @@ using a regular always may be more appropriate.
 Ignoring this warning will only suppress the lint check, it will simulate
 correctly.
 
+=item NULLPORT
+
+Warns that a null port was detected in the module definition port list. Null
+ports are empty placeholders, i.e. either one ore more commas at the beginning
+or the end of a module port list, or two or more consecutive commas in the
+middle of a module port list. A null port cannot be accessed within the module,
+but when instantiating the module by port order, it is treated like a regular
+port and any wire connected to it is left unconnected.
+This is considered a warning because this feature is rarely used, and is mostly
+the result of a typing error such as a dangling comma at the end of a port list.
+
 =item PINCONNECTEMPTY
 
 Warns that an instance has a pin which is connected to .pin_name(),

src/V3Error.h

@@ -101,6 +101,7 @@ public:
         MULTIDRIVEN,    // Driven from multiple blocks
         MULTITOP,       // Multiple top level modules
         NOLATCH,        // No latch detected in always_latch block
+        NULLPORT,       // Null port detected in module definition
         PINCONNECTEMPTY,// Cell pin connected by name with empty reference
         PINMISSING,     // Cell pin not specified
         PINNOCONNECT,   // Cell pin not connected
@@ -167,7 +168,7 @@ public:
             "IMPERFECTSCH", "IMPLICIT", "IMPORTSTAR", "IMPURE",
             "INCABSPATH", "INFINITELOOP", "INITIALDLY", "INSECURE",
             "LATCH", "LITENDIAN", "MODDUP",
-            "MULTIDRIVEN", "MULTITOP","NOLATCH", "PINCONNECTEMPTY",
+            "MULTIDRIVEN", "MULTITOP","NOLATCH", "NULLPORT", "PINCONNECTEMPTY",
             "PINMISSING", "PINNOCONNECT",  "PINNOTFOUND", "PKGNODECL", "PROCASSWIRE",
             "RANDC", "REALCVT", "REDEFMACRO",
             "SELRANGE", "SHORTREAL", "SPLITVAR", "STMTDLY", "SYMRSVDWORD", "SYNCASYNCNET",

src/verilog.y

@@ -1284,9 +1284,31 @@ portsStarE<nodep>:		// IEEE: .* + list_of_ports + list_of_port_declarations + em
 	|	'(' {VARRESET_LIST(PORT);} list_of_ports ')'	{ $$ = $3; VARRESET_NONLIST(UNKNOWN); }
 	;
 
+list_of_portsE<nodep>:		// IEEE: list_of_ports + list_of_port_declarations
+		portAndTagE			{ $$ = $1; }
+	|	list_of_portsE ',' portAndTagE		{ $$ = $1->addNextNull($3); }
+	;
+
 list_of_ports<nodep>:		// IEEE: list_of_ports + list_of_port_declarations
-		portAndTag				{ $$ = $1; }
+		portAndTag			{ $$ = $1; }
-	|	list_of_ports ',' portAndTag		{ $$ = $1->addNextNull($3); }
+	|	list_of_portsE ',' portAndTagE		{ $$ = $1->addNextNull($3); }
+	;
+
+portAndTagE<nodep>:
+		/* empty */
+			{ int p = PINNUMINC();
+			   const string name = "__pinNumber" + cvtToStr(p);
+			  $$ = new AstPort{CRELINE(), p, name};
+			  AstVar* varp = new AstVar{CRELINE(), AstVarType::PORT, name, VFlagChildDType{},
+			                            new AstBasicDType{CRELINE(), LOGIC_IMPLICIT}};
+			  varp->declDirection(VDirection::INPUT);
+			  varp->direction(VDirection::INPUT);
+			  varp->ansi(false);
+			  varp->declTyped(true);
+			  varp->trace(false);
+			  $$ = $$->addNext(varp);
+			  $$->v3warn(NULLPORT, "Null port on module (perhaps extraneous comma)"); }
+	|	portAndTag				{ $$ = $1; }
 	;
 
 portAndTag<nodep>:

test_regress/t/t_lint_nullport.out

@@ -0,0 +1,107 @@
+%Warning-NULLPORT: t/t_lint_nullport.v:23:13: Null port on module (perhaps extraneous comma)
+   23 | module t5(a,);
+      |             ^
+                   ... Use "/* verilator lint_off NULLPORT */" and lint_on around source to disable this message.
+%Warning-NULLPORT: t/t_lint_nullport.v:27:13: Null port on module (perhaps extraneous comma)
+   27 | module t6(a,,);
+      |             ^
+%Warning-NULLPORT: t/t_lint_nullport.v:27:14: Null port on module (perhaps extraneous comma)
+   27 | module t6(a,,);
+      |              ^
+%Warning-NULLPORT: t/t_lint_nullport.v:31:15: Null port on module (perhaps extraneous comma)
+   31 | module t7(a,b,);
+      |               ^
+%Warning-NULLPORT: t/t_lint_nullport.v:35:15: Null port on module (perhaps extraneous comma)
+   35 | module t8(a,b,,);
+      |               ^
+%Warning-NULLPORT: t/t_lint_nullport.v:35:16: Null port on module (perhaps extraneous comma)
+   35 | module t8(a,b,,);
+      |                ^
+%Warning-NULLPORT: t/t_lint_nullport.v:39:13: Null port on module (perhaps extraneous comma)
+   39 | module t9(a,,b);
+      |             ^
+%Warning-NULLPORT: t/t_lint_nullport.v:43:14: Null port on module (perhaps extraneous comma)
+   43 | module t10(a,,b,);
+      |              ^
+%Warning-NULLPORT: t/t_lint_nullport.v:43:17: Null port on module (perhaps extraneous comma)
+   43 | module t10(a,,b,);
+      |                 ^
+%Warning-NULLPORT: t/t_lint_nullport.v:47:14: Null port on module (perhaps extraneous comma)
+   47 | module t11(a,,b,,);
+      |              ^
+%Warning-NULLPORT: t/t_lint_nullport.v:47:17: Null port on module (perhaps extraneous comma)
+   47 | module t11(a,,b,,);
+      |                 ^
+%Warning-NULLPORT: t/t_lint_nullport.v:47:18: Null port on module (perhaps extraneous comma)
+   47 | module t11(a,,b,,);
+      |                  ^
+%Warning-NULLPORT: t/t_lint_nullport.v:51:12: Null port on module (perhaps extraneous comma)
+   51 | module t12(,a,,b);
+      |            ^
+%Warning-NULLPORT: t/t_lint_nullport.v:51:15: Null port on module (perhaps extraneous comma)
+   51 | module t12(,a,,b);
+      |               ^
+%Warning-NULLPORT: t/t_lint_nullport.v:55:12: Null port on module (perhaps extraneous comma)
+   55 | module t13(,a,,b,);
+      |            ^
+%Warning-NULLPORT: t/t_lint_nullport.v:55:15: Null port on module (perhaps extraneous comma)
+   55 | module t13(,a,,b,);
+      |               ^
+%Warning-NULLPORT: t/t_lint_nullport.v:55:18: Null port on module (perhaps extraneous comma)
+   55 | module t13(,a,,b,);
+      |                  ^
+%Warning-NULLPORT: t/t_lint_nullport.v:59:12: Null port on module (perhaps extraneous comma)
+   59 | module t14(,a,,b,,);
+      |            ^
+%Warning-NULLPORT: t/t_lint_nullport.v:59:15: Null port on module (perhaps extraneous comma)
+   59 | module t14(,a,,b,,);
+      |               ^
+%Warning-NULLPORT: t/t_lint_nullport.v:59:18: Null port on module (perhaps extraneous comma)
+   59 | module t14(,a,,b,,);
+      |                  ^
+%Warning-NULLPORT: t/t_lint_nullport.v:59:19: Null port on module (perhaps extraneous comma)
+   59 | module t14(,a,,b,,);
+      |                   ^
+%Warning-NULLPORT: t/t_lint_nullport.v:63:12: Null port on module (perhaps extraneous comma)
+   63 | module t15(,,a,,b);
+      |            ^
+%Warning-NULLPORT: t/t_lint_nullport.v:63:13: Null port on module (perhaps extraneous comma)
+   63 | module t15(,,a,,b);
+      |             ^
+%Warning-NULLPORT: t/t_lint_nullport.v:63:16: Null port on module (perhaps extraneous comma)
+   63 | module t15(,,a,,b);
+      |                ^
+%Warning-NULLPORT: t/t_lint_nullport.v:67:12: Null port on module (perhaps extraneous comma)
+   67 | module t16(,,a,,b,);
+      |            ^
+%Warning-NULLPORT: t/t_lint_nullport.v:67:13: Null port on module (perhaps extraneous comma)
+   67 | module t16(,,a,,b,);
+      |             ^
+%Warning-NULLPORT: t/t_lint_nullport.v:67:16: Null port on module (perhaps extraneous comma)
+   67 | module t16(,,a,,b,);
+      |                ^
+%Warning-NULLPORT: t/t_lint_nullport.v:67:19: Null port on module (perhaps extraneous comma)
+   67 | module t16(,,a,,b,);
+      |                   ^
+%Warning-NULLPORT: t/t_lint_nullport.v:71:12: Null port on module (perhaps extraneous comma)
+   71 | module t17(,,a,,b,,);
+      |            ^
+%Warning-NULLPORT: t/t_lint_nullport.v:71:13: Null port on module (perhaps extraneous comma)
+   71 | module t17(,,a,,b,,);
+      |             ^
+%Warning-NULLPORT: t/t_lint_nullport.v:71:16: Null port on module (perhaps extraneous comma)
+   71 | module t17(,,a,,b,,);
+      |                ^
+%Warning-NULLPORT: t/t_lint_nullport.v:71:19: Null port on module (perhaps extraneous comma)
+   71 | module t17(,,a,,b,,);
+      |                   ^
+%Warning-NULLPORT: t/t_lint_nullport.v:71:20: Null port on module (perhaps extraneous comma)
+   71 | module t17(,,a,,b,,);
+      |                    ^
+%Warning-NULLPORT: t/t_lint_nullport.v:75:12: Null port on module (perhaps extraneous comma)
+   75 | module t18(,);
+      |            ^
+%Warning-NULLPORT: t/t_lint_nullport.v:75:13: Null port on module (perhaps extraneous comma)
+   75 | module t18(,);
+      |             ^
+%Error: Exiting due to

test_regress/t/t_lint_nullport.pl

@@ -0,0 +1,19 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2021 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(linter => 1);
+
+lint(
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;

test_regress/t/t_lint_nullport.v

@@ -0,0 +1,80 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2021 by Udi Finkelstein.
+// SPDX-License-Identifier: CC0-1.0
+
+/* verilator lint_off MULTITOP */
+// First, test we haven't broken normal ports
+module t1();
+endmodule
+
+module t2;
+endmodule
+
+module t3(a);
+input a;
+endmodule
+
+module t4(a, b);
+input a, b;
+endmodule
+
+module t5(a,);
+input a;
+endmodule
+
+module t6(a,,);
+input a;
+endmodule
+
+module t7(a,b,);
+input a, b;
+endmodule
+
+module t8(a,b,,);
+input a, b;
+endmodule
+
+module t9(a,,b);
+input a, b;
+endmodule
+
+module t10(a,,b,);
+input a, b;
+endmodule
+
+module t11(a,,b,,);
+input a, b;
+endmodule
+
+module t12(,a,,b);
+input a, b;
+endmodule
+
+module t13(,a,,b,);
+input a, b;
+endmodule
+
+module t14(,a,,b,,);
+input a, b;
+endmodule
+
+module t15(,,a,,b);
+input a, b;
+endmodule
+
+module t16(,,a,,b,);
+input a, b;
+endmodule
+
+module t17(,,a,,b,,);
+input a, b;
+endmodule
+
+module t18(,);
+endmodule
+
+/* verilator lint_off NULLPORT */
+module t19(,,);
+endmodule