From f6ff5b4cfbdf54327f4b7d9ee435a9785c99584c Mon Sep 17 00:00:00 2001
From: Ethan Sifferman <ethan@sifferman.dev>
Date: Fri, 25 Sep 2026 14:34:47 -0700
Subject: [PATCH] Fix elaboration of classes reached through deferred
 references (#8440) (#8510)

---
 src/V3Param.cpp                               | 21 +++++++++++
 .../t/t_class_lparam_type_param_override.py   | 16 +++++++++
 .../t/t_class_lparam_type_param_override.v    | 36 +++++++++++++++++++
 3 files changed, 73 insertions(+)
 create mode 100755 test_regress/t/t_class_lparam_type_param_override.py
 create mode 100644 test_regress/t/t_class_lparam_type_param_override.v

diff --git a/src/V3Param.cpp b/src/V3Param.cpp
index 6465b7ce8..9ca2b66ba 100644
--- a/src/V3Param.cpp
+++ b/src/V3Param.cpp
@@ -309,6 +309,8 @@ class ParamProcessor final {
     // Guard against infinite recursion in classTypeMatchesDefaultClone slow path
     std::unordered_set<const AstClass*> m_defaultCloneInProgress;
 
+    std::vector<AstClass*> m_specializedClassps;  // Classes specialized since last drained
+
     // member names cached for fast lookup
     VMemberMap m_memberMap;
 
@@ -2143,6 +2145,14 @@ class ParamProcessor final {
         const bool cloned = (newModp != srcModp);
         UINFO(9, "nodeDeparamCommon result: " << newModp->prettyNameQ() << " cloned=" << cloned);
 
+        // ParamVisitor skips the body of a class still marked hasGParam(), relying on it
+        // being visited through a reference instead.  A class reached only by a deferred
+        // class-scoped reference (e.g. the 'C#(V)::t' default of a type parameter that the
+        // instantiation overrides) is never visited, so record specializations here.
+        // user2() is set once processWorkQ has elaborated the body, which needs no re-queue.
+        AstClass* const newClassp = VN_CAST(newModp, Class);
+        if (newClassp && !newClassp->user2()) m_specializedClassps.push_back(newClassp);
+
         // Link source class to its specialized version for later relinking of method references
         if (defaultsResolved) srcModp->user4p(newModp);
 
@@ -2455,6 +2465,13 @@ public:
         return newModp;
     }
 
+    // Return, and forget, the classes specialized since the previous call
+    std::vector<AstClass*> takeSpecializedClassps() {
+        std::vector<AstClass*> taken;
+        taken.swap(m_specializedClassps);
+        return taken;
+    }
+
     // CONSTRUCTORS
     explicit ParamProcessor(AstNetlist* nodep)
         : m_hierBlocks{v3Global.opt.hierBlocks(), nodep} {
@@ -2775,6 +2792,10 @@ class ParamVisitor final : public VNVisitor {
 
         // Visit all cells under module, recursively
         while (true) {
+            // Classes specialized since the last pass still need their bodies elaborated
+            for (AstClass* const classp : m_processor.takeSpecializedClassps()) {
+                m_state.m_workQueueNext.emplace(ParamState::WQKey{true, classp->level()}, classp);
+            }
             if (workQueue.empty()) std::swap(workQueue, m_state.m_workQueueNext);
             if (workQueue.empty()) break;
 
diff --git a/test_regress/t/t_class_lparam_type_param_override.py b/test_regress/t/t_class_lparam_type_param_override.py
new file mode 100755
index 000000000..a5ea6627e
--- /dev/null
+++ b/test_regress/t/t_class_lparam_type_param_override.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('linter')
+
+test.lint()
+
+test.passes()
diff --git a/test_regress/t/t_class_lparam_type_param_override.v b/test_regress/t/t_class_lparam_type_param_override.v
new file mode 100644
index 000000000..0e8c160f0
--- /dev/null
+++ b/test_regress/t/t_class_lparam_type_param_override.v
@@ -0,0 +1,36 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// SPDX-FileCopyrightText: 2026 Ethan Sifferman
+// SPDX-License-Identifier: CC0-1.0
+
+// Overriding a type parameter whose default is a parameterized class scope
+// still specializes the class, so its body must be elaborated (#8440).
+
+package pkg;
+  function automatic integer func();
+    return 1;
+  endfunction
+endpackage
+
+class class_with_package_call #(
+    parameter int unused_param = 0
+);
+  typedef int value_t;
+  localparam int local_param = pkg::func();
+endclass
+
+module module_with_type_parameter #(
+    parameter type value_t = class_with_package_call#(0)::value_t
+);
+endmodule
+
+interface iface_with_type_parameter #(
+    parameter type value_t = class_with_package_call#(1)::value_t
+) ();
+  value_t value;
+endinterface
+
+module top;
+  module_with_type_parameter #(.value_t(logic signed [15:0])) dut ();
+  iface_with_type_parameter #(.value_t(logic signed [15:0])) itf ();
+endmodule