Fix parameterized class nested in a parameterized interface (#8328) (#8329)

docs/CONTRIBUTORS

@@ -183,6 +183,7 @@ Keith Colbert
 Kevin Kiningham
 Kevin Nygaard
 Kornel Uriasz
+Kristof Marien
 Kritik Bhimani
 Krzysztof Bieganski
 Krzysztof Boronski

src/V3Param.cpp

@@ -961,6 +961,12 @@ class ParamProcessor final {
         } else {
             newModp = srcModp->cloneTree(false);
         }
+        // AstPin normally retains links to external module formals across cloning. For a cloned
+        // interface, relink pins whose formals were cloned with the interface while clonep() is
+        // still valid, so nested parameterized classes use the cloned interface parameters.
+        if (AstIface* const newIfacep = VN_CAST(newModp, Iface)) {
+            newIfacep->foreach([](AstPin* pinp) { pinp->cloneRelinkGen(); });
+        }
 
         // Mark the source module as a parameterized template now that a specialized
         // clone exists.  This suppresses width/type errors on the unresolved template

test_regress/t/t_interface_param_nested_class.py

@@ -0,0 +1,18 @@
+#!/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_all')
+
+test.compile()
+
+test.execute()
+
+test.passes()

test_regress/t/t_interface_param_nested_class.v

@@ -0,0 +1,24 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2026 by Verilator Authors.
+// SPDX-FileCopyrightText: 2026 Wilson Snyder
+// SPDX-License-Identifier: CC0-1.0
+
+// A parameterized class nested in a specialized parameterized interface must
+// produce distinct, well-formed class-package names during C++ emission.
+interface intf #(int P = 1);
+  class Cls #(int Q);
+  endclass
+
+  Cls #(P) obj;
+endinterface
+
+module t;
+  intf #(2) intf_i();
+
+  initial begin
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule