Fix WIDTH warnings on comparisons with nullptr (#2602).

Changes

@@ -6,6 +6,8 @@ The contributors that suggested a given feature are shown in []. Thanks!
 
 ****  Support queue slicing (#2326).
 
+****  Fix WIDTH warnings on comparisons with nullptr (#2602). [Rupert Swarbrick]
+
 
 * Verilator 4.102 2020-10-15
 

src/V3Width.cpp

@@ -4781,6 +4781,12 @@ private:
                 = new AstNeqD(nodep->fileline(), underp,
                               new AstConst(nodep->fileline(), AstConst::RealDouble(), 0.0));
             linker.relink(newp);
+        } else if (VN_IS(underp->dtypep(), ClassRefDType)
+                   || (VN_IS(underp->dtypep(), BasicDType)
+                       && VN_CAST(underp->dtypep(), BasicDType)->keyword()
+                              == AstBasicDTypeKwd::CHANDLE)) {
+            // Allow warning-free "if (handle)"
+            VL_DO_DANGLING(fixWidthReduce(underp), underp);  // Changed
         } else if (!underp->dtypep()->basicp()) {
             nodep->v3error("Logical operator " << nodep->prettyTypeName()
                                                << " expects a non-complex data type on the "

src/verilog.y

@@ -4228,7 +4228,7 @@ expr<nodep>:			// IEEE: part of expression/constant_expression/primary
 	//			// Indistinguishable from function_subroutine_call:method_call
 	//
 	|	'$'					{ $$ = new AstUnbounded($<fl>1); }
-	|	yNULL					{ $$ = new AstConst($1, AstConst::LogicFalse()); }
+	|	yNULL					{ $$ = new AstConst($1, AstConst::StringToParse(), "'0"); }
 	//			// IEEE: yTHIS
 	//			// See exprScope
 	//

test_regress/t/t_class1.v

@@ -15,8 +15,11 @@ module t (/*AUTOARG*/);
    initial begin
       Cls c;
       if (c != null) $stop;
+      if (c) $stop;
       $display("Display: null = \"%p\"", c);  // null
       c = new;
+      if (c == null) $stop;
+      if (!c) $stop;
       $display("Display: newed = \"%p\"", c);  // '{imembera:0, imemberb:0}
       c.imembera = 10;
       c.imemberb = 20;

test_regress/t/t_var_types.v

@@ -216,6 +216,11 @@ module t (/*AUTOARG*/);
       d_time = $time;
       if ($time !== d_time) $stop;
 
+      // Null checks
+      d_chandle = null;
+      if (d_chandle != null) $stop;
+      if (d_chandle) $stop;
+
       $write("*-* All Finished *-*\n");
       $finish;
    end