Fix virtual class inheritance (#7403) (#7405)

Fixes #7403.

docs/CONTRIBUTORS

@@ -197,6 +197,7 @@ Nathan Graybeal
 Nathan Kohagen
 Nathan Myers
 Nick Brereton
+Nikolay Puzanov
 Nolan Poe
 Oleh Maksymenko
 Patrick Stewart

src/V3LinkDot.cpp

@@ -3406,7 +3406,7 @@ class LinkDotResolveVisitor final : public VNVisitor {
                     if (!baseFuncp || !baseFuncp->pureVirtual()) continue;
                     const bool existsInDerived = foundp && !foundp->imported();
                     if (m_statep->forPrimary() && !existsInDerived
-                        && !derivedClassp->isInterfaceClass()) {
+                        && !derivedClassp->isInterfaceClass() && !derivedClassp->isVirtual()) {
                         derivedClassp->v3error(
                             "Class " << derivedClassp->prettyNameQ() << impOrExtends
                                      << baseClassp->prettyNameQ()

test_regress/t/t_class_virtual_extends_pure.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# 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-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+
+test.lint()
+
+test.passes()

test_regress/t/t_class_virtual_extends_pure.v

@@ -0,0 +1,23 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2026 Wilson Snyder
+// SPDX-License-Identifier: CC0-1.0
+
+virtual class Base;
+  pure virtual function void f0();
+endclass
+
+virtual class Child extends Base;
+  pure virtual function void f1();
+endclass
+
+class Impl extends Child;
+  virtual function void f0();
+  endfunction
+  virtual function void f1();
+  endfunction
+endclass
+
+module t;
+endmodule