Add error when trying to assign class object to variable of non-class types (#6237)

src/V3Width.cpp

@@ -7329,21 +7329,26 @@ class WidthVisitor final : public VNVisitor {
         }
         return false;
     }
-    void checkClassAssign(AstNode* nodep, const char* side, AstNode* rhsp,
+    void checkClassAssign(const AstNode* nodep, const char* side, AstNode* rhsp,
                           AstNodeDType* const lhsDTypep) {
-        if (AstClassRefDType* const lhsClassRefp = VN_CAST(lhsDTypep->skipRefp(), ClassRefDType)) {
-            UASSERT_OBJ(rhsp->dtypep(), rhsp, "Node has no type");
-            AstNodeDType* const rhsDtypep = rhsp->dtypep()->skipRefp();
-            if (AstClassRefDType* const rhsClassRefp = VN_CAST(rhsDtypep, ClassRefDType)) {
+        UASSERT_OBJ(rhsp->dtypep(), rhsp, "Node has no type");
+        const AstNodeDType* const lhsRawDTypep = lhsDTypep->skipRefp();
+        const AstNodeDType* const rhsRawDTypep = rhsp->dtypep()->skipRefp();
+        if (const AstClassRefDType* const lhsClassRefp = VN_CAST(lhsRawDTypep, ClassRefDType)) {
+            if (const AstClassRefDType* const rhsClassRefp
+                = VN_CAST(rhsRawDTypep, ClassRefDType)) {
                 if (isBaseClassRecurse(lhsClassRefp->classp(), rhsClassRefp->classp())) return;
             } else if (rhsp->isNull()) {
                 return;
             }
             nodep->v3error(side << " expects a " << lhsClassRefp->prettyTypeName() << ", got "
-                                << rhsDtypep->prettyTypeName());
+                                << rhsRawDTypep->prettyTypeName());
+        } else if (VN_IS(rhsRawDTypep, ClassRefDType)) {
+            nodep->v3error(side << " " << rhsRawDTypep->prettyDTypeNameQ()
+                                << " cannot be assigned to non-class "
+                                << lhsDTypep->prettyDTypeNameQ());
         }
-        if (VN_IS(lhsDTypep->skipRefp(), DynArrayDType)
-            && VN_IS(rhsp->dtypep()->skipRefp(), UnpackArrayDType)) {
+        if (VN_IS(lhsRawDTypep, DynArrayDType) && VN_IS(rhsRawDTypep, UnpackArrayDType)) {
             VNRelinker relinker;
             rhsp->unlinkFrBack(&relinker);
             relinker.relink(

test_regress/t/t_class_to_basic_assignment_bad.out

@@ -0,0 +1,5 @@
+%Error: t/t_class_to_basic_assignment_bad.v:26:29: Assign RHS 'class{}Foo' cannot be assigned to non-class 'int'
+   26 |         new_node.phase_done = get();
+      |                             ^
+        ... See the manual at https://verilator.org/verilator_doc.html?v=latest for more assistance.
+%Error: Exiting due to

test_regress/t/t_class_to_basic_assignment_bad.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 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
+
+import vltest_bootstrap
+
+test.scenarios('linter')
+
+test.lint(fails=True, expect_filename=test.golden_filename)
+
+test.passes()

test_regress/t/t_class_to_basic_assignment_bad.v

@@ -0,0 +1,32 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Antmicro.
+// SPDX-License-Identifier: CC0-1.0
+
+class Foo;
+  int phase_done;
+
+  static function Foo get();
+    Foo ans = new;
+    return ans;
+  endfunction
+
+  static function int create ();
+    return 3;
+  endfunction
+
+  function string get_name ();
+    return "bar";
+  endfunction
+
+  function void add(Foo phase);
+    Foo new_node;
+    if (new_node.get_name() == "run") begin
+        new_node.phase_done = get();
+    end
+    else begin
+        new_node.phase_done = create();
+    end
+  endfunction
+endclass

test_regress/t/t_process_copy_constr.v

@@ -7,7 +7,7 @@
 class Cls;
    int x = 1;
    function new();
-      int p = process::self();
+      process p = process::self();
    endfunction
 endclass