Support enum.next with a parameter

src/V3Width.cpp

@@ -3550,12 +3550,18 @@ class WidthVisitor final : public VNVisitor {
             }
 
             if (nodep->name() != "name" && nodep->pinsp()) {
-                AstNodeExpr* const stepp = methodArg(nodep, 0);
+                AstNodeExpr* stepp = methodArg(nodep, 0);
+                VL_DO_DANGLING(V3Const::constifyParamsNoWarnEdit(stepp), stepp);
+                stepp = methodArg(nodep, 0);
                 nodep->fileline()->modifyWarnOff(V3ErrorCode::WIDTHEXPAND, true);
                 iterateCheckUInt32(nodep, "argument", stepp, BOTH);
                 if (!VN_IS(stepp, Const)) {
-                    stepp->v3fatalSrc("Unsupported: enum next/prev with non-const argument");
-                } else {
+                    stepp->v3warn(E_UNSUPPORTED,
+                                  "Unsupported: enum next/prev with non-constant argument");
+                    AstNodeExpr* const newp = new AstConst{stepp->fileline(), 1};
+                    stepp->replaceWith(newp);
+                    stepp = newp;
+                }
                 const uint32_t stepWidth = VN_AS(stepp, Const)->toUInt();
                 if (stepWidth == 0) {
                     // Step of 0 "legalizes" like $cast, use .next.prev
@@ -3583,7 +3589,6 @@ class WidthVisitor final : public VNVisitor {
                     return;
                 }
             }
-            }
             AstNodeExpr* const newp
                 = enumSelect(nodep->fromp()->unlinkFrBack(), adtypep, attrType);
             nodep->replaceWith(newp);

test_regress/t/t_enum_type_methods.v

@@ -40,7 +40,7 @@ module t (/*AUTOARG*/
       `checkh(e.next(2), E01);
       `checkh(e.next(1).next(1).next(1), E03);
       `checkh(e.next(1).next(2), E03);
-      `checkh(e.next(3), E03);
+      `checkh(e.next(THREE), E03);
       `checkh(e.prev, E01);
       `checkh(e.prev(1), E01);
       `checkh(e.prev(1).prev(1), E04);
@@ -57,6 +57,8 @@ module t (/*AUTOARG*/
       `checks(all, "E01E03E04");
    end
 
+   localparam THREE = 3;
+
    // Check runtime
    always @ (posedge clk) begin
       cyc <= cyc + 1;

test_regress/t/t_enum_type_methods_bad.out

@@ -1,5 +1,6 @@
-%Error: Internal Error: t/t_enum_type_methods_bad.v:24:14: ../V3Width.cpp:#: Unsupported: enum next/prev with non-const argument
+%Error-UNSUPPORTED: t/t_enum_type_methods_bad.v:24:14: Unsupported: enum next/prev with non-constant argument
                                                      : ... note: In instance 't'
    24 |       e.next(increment);
       |              ^~~~~~~~~
-                        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
+                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
+%Error: Exiting due to