From 651f2233876cc2c6b7fce5d19ee186042cad0081 Mon Sep 17 00:00:00 2001
From: Alex Zhou <126853855+aexzhou@users.noreply.github.com>
Date: Mon, 16 Mar 2026 04:31:35 -0700
Subject: [PATCH] Fix false recursive definition error (#6769) (#7118)

---
 src/V3Param.cpp                          | 51 ++++++++++++++++++++++++
 test_regress/t/t_recursive_definition.py | 18 +++++++++
 test_regress/t/t_recursive_definition.v  | 30 ++++++++++++++
 3 files changed, 99 insertions(+)
 create mode 100755 test_regress/t/t_recursive_definition.py
 create mode 100644 test_regress/t/t_recursive_definition.v

diff --git a/src/V3Param.cpp b/src/V3Param.cpp
index 3882b8a3d..db786047e 100644
--- a/src/V3Param.cpp
+++ b/src/V3Param.cpp
@@ -1913,6 +1913,55 @@ public:
     void visit(AstNode* nodep) override { iterateChildren(nodep); }
 };
 
+//######################################################################
+//  Relink RefDType nodes to point to parameterized classes' type parameters
+
+class ParamClassRefDTypeRelinkVisitor final : public VNVisitor {
+
+    AstClass* m_classp = nullptr;
+    std::unordered_map<const AstParamTypeDType*, AstClass*> m_paramTypeClassMap;
+
+public:
+    explicit ParamClassRefDTypeRelinkVisitor(AstNetlist* netlistp) { iterate(netlistp); }
+    void visit(AstClass* nodep) override {
+        VL_RESTORER(m_classp);
+        m_classp = nodep;
+        for (AstNode* stmtp = nodep->stmtsp(); stmtp; stmtp = stmtp->nextp()) {
+            if (AstParamTypeDType* const ptp = VN_CAST(stmtp, ParamTypeDType)) {
+                m_paramTypeClassMap[ptp] = nodep;
+            }
+        }
+        iterateChildren(nodep);
+    }
+    void visit(AstRefDType* nodep) override {
+        iterateChildren(nodep);
+        AstParamTypeDType* const paramtypep = VN_CAST(nodep->refDTypep(), ParamTypeDType);
+        if (!paramtypep) return;
+        const auto it = m_paramTypeClassMap.find(paramtypep);
+        if (it == m_paramTypeClassMap.end()) return;
+        AstClass* const origClassp = it->second;
+        if (!origClassp->hasGParam()) return;  // only relink refs to original param classes
+        if (origClassp->user3p()) return;  // will not get removed, no need to relink
+        AstClass* const parametrizedClassp = VN_CAST(origClassp->user4p(), Class);
+        if (!parametrizedClassp) return;
+        const string paramName = paramtypep->name();
+        AstParamTypeDType* newParamTypep = nullptr;
+        for (AstNode* stmtp = parametrizedClassp->stmtsp(); stmtp; stmtp = stmtp->nextp()) {
+            if (AstParamTypeDType* const ptp = VN_CAST(stmtp, ParamTypeDType)) {
+                if (ptp->name() == paramName) {
+                    newParamTypep = ptp;
+                    break;
+                }
+            }
+        }
+        if (newParamTypep) {
+            nodep->refDTypep(newParamTypep);
+            nodep->classOrPackagep(parametrizedClassp);
+        }
+    }
+    void visit(AstNode* nodep) override { iterateChildren(nodep); }
+};
+
 //######################################################################
 // Process parameter top state
 
@@ -2784,6 +2833,8 @@ public:
             }
         });
 
+        ParamClassRefDTypeRelinkVisitor paramClassDTypeRelinkVisitor{netlistp};
+
         relinkDots();
 
         resortNetlistModules(netlistp);
diff --git a/test_regress/t/t_recursive_definition.py b/test_regress/t/t_recursive_definition.py
new file mode 100755
index 000000000..3cc73805c
--- /dev/null
+++ b/test_regress/t/t_recursive_definition.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: 2024 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile()
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_recursive_definition.v b/test_regress/t/t_recursive_definition.v
new file mode 100644
index 000000000..15e2fca90
--- /dev/null
+++ b/test_regress/t/t_recursive_definition.v
@@ -0,0 +1,30 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2023 Antmicro Ltd
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+  class uvm_built_in_comp #(
+    type T = int
+  );
+  endclass
+
+  class uvm_in_order_comparator #(
+    type T = int,
+    type comp_type = uvm_built_in_comp#(T)
+  );
+  endclass
+
+  class uvm_in_order_built_in_comparator #(
+    type T = int
+  ) extends uvm_in_order_comparator #(T);
+  endclass
+
+  initial begin
+    uvm_in_order_built_in_comparator #(int) sb;
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule