Add lint check for bad enum 4-state values.

src/V3Width.cpp

@@ -1452,6 +1452,8 @@ private:
             if (!itemp->valuep()) {
                 if (num.isEqZero() && itemp != nodep->itemsp())
                     itemp->v3error("Enum value illegally wrapped around (IEEE 2017 6.19)");
+                if (num.isFourState())
+                    itemp->v3error("Enum value that is unassigned cannot follow value with X/Zs (IEEE 2017 6.19)");
                 if (!nodep->dtypep()->basicp()
                     && !nodep->dtypep()->basicp()->keyword().isIntNumeric()) {
                     itemp->v3error("Enum names without values only allowed on numeric types");
@@ -1459,7 +1461,12 @@ private:
                 }
                 itemp->valuep(new AstConst(itemp->fileline(), num));
             }
-            num.opAssign(VN_CAST(itemp->valuep(), Const)->num());
+
+            AstConst* constp = VN_CAST(itemp->valuep(), Const);
+            if (constp->num().isFourState() && nodep->dtypep()->basicp()
+                && !nodep->dtypep()->basicp()->isFourstate())
+                itemp->v3error("Enum value with X/Zs cannot be assigned to non-fourstate type (IEEE 2019 6.19)");
+            num.opAssign(constp->num());
             // Look for duplicates
             if (inits.find(num) != inits.end()) {  // IEEE says illegal
                 AstNode* otherp = inits.find(num)->second;
@@ -1471,7 +1478,7 @@ private:
             } else {
                 inits.insert(make_pair(num, itemp));
             }
-            num.opAdd(one, VN_CAST(itemp->valuep(), Const)->num());
+            num.opAdd(one, constp->num());
         }
     }
     virtual void visit(AstEnumItem* nodep) {

test_regress/t/t_enum_x_bad.out

@@ -0,0 +1,9 @@
+%Error: t/t_enum_x_bad.v:8: Enum value with X/Zs cannot be assigned to non-fourstate type (IEEE 2019 6.19)
+                          : ... In instance t
+   enum bit [1:0] { BADX = 2'b1x } BAD1;
+                    ^~~~
+%Error: t/t_enum_x_bad.v:11: Enum value that is unassigned cannot follow value with X/Zs (IEEE 2017 6.19)
+                           : ... In instance t
+                      e1
+                      ^~
+%Error: Exiting due to

test_regress/t/t_enum_x_bad.pl

@@ -0,0 +1,18 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2008 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.
+
+scenarios(linter => 1);
+
+lint(
+    fails => 1,
+    expect_filename => $Self->{golden_filename},
+    );
+
+ok(1);
+1;

test_regress/t/t_enum_x_bad.v

@@ -0,0 +1,18 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2009 by Wilson Snyder.
+
+module t (/*AUTOARG*/);
+
+   enum bit [1:0] { BADX = 2'b1x } BAD1;
+
+   enum logic [3:0] { e0 = 4'b1xx1,
+                      e1
+                      } BAD2;
+
+   initial begin
+      $stop;
+   end
+
+endmodule