From a4ad255438dbd0f2ff52eef42c2a6578f0d2c2ee Mon Sep 17 00:00:00 2001
From: Alex Zhou <126853855+aexzhou@users.noreply.github.com>
Date: Fri, 20 Feb 2026 21:43:22 -0800
Subject: [PATCH] Fix extending class by a typedef (#6679) (#6855)

---
 docs/CONTRIBUTORS                        |  1 +
 src/V3LinkDot.cpp                        | 17 +++++++++++++++++
 test_regress/t/t_class_extends_alias.out |  5 -----
 test_regress/t/t_class_extends_alias.py  |  6 ++++--
 4 files changed, 22 insertions(+), 7 deletions(-)
 delete mode 100644 test_regress/t/t_class_extends_alias.out

diff --git a/docs/CONTRIBUTORS b/docs/CONTRIBUTORS
index b3e411363..34b80c77f 100644
--- a/docs/CONTRIBUTORS
+++ b/docs/CONTRIBUTORS
@@ -12,6 +12,7 @@ Aidan McNay
 Aleksander Kiryk
 Alex Chadwick
 Alex Solomatnikov
+Alex Zhou
 Aliaksei Chapyzhenka
 Ameya Vikram Singh
 Andrea Calabrese
diff --git a/src/V3LinkDot.cpp b/src/V3LinkDot.cpp
index 2c22bf1a2..404dcec95 100644
--- a/src/V3LinkDot.cpp
+++ b/src/V3LinkDot.cpp
@@ -5381,6 +5381,23 @@ class LinkDotResolveVisitor final : public VNVisitor {
                 refParamp->refDTypep(paramp);
                 nodep->childDTypep(refParamp);
                 nodep->parameterized(true);
+            } else if (AstTypedef* const typedefp = VN_CAST(foundp->nodep(), Typedef)) {
+                AstNodeDType* const unwrappedp = typedefp->subDTypep()->skipRefp();
+                if (AstClassRefDType* const classRefp = VN_CAST(unwrappedp, ClassRefDType)) {
+                    AstPin* paramsp = cpackagerefp->paramsp();
+                    if (paramsp) {
+                        paramsp = paramsp->cloneTree(true);
+                        nodep->parameterized(true);
+                    }
+                    nodep->childDTypep(new AstClassRefDType{nodep->fileline(), classRefp->classp(), paramsp});
+                    iterate(nodep->childDTypep());
+                }
+                else {
+                    nodep->v3warn(E_UNSUPPORTED,
+                        "Unsupported: " << foundp->nodep()->prettyTypeName()
+                                        << " in 'class extends'");
+                    return;
+                }
             } else {
                 nodep->v3warn(E_UNSUPPORTED, "Unsupported: " << foundp->nodep()->prettyTypeName()
                                                              << " in 'class extends'");
diff --git a/test_regress/t/t_class_extends_alias.out b/test_regress/t/t_class_extends_alias.out
deleted file mode 100644
index f668ed890..000000000
--- a/test_regress/t/t_class_extends_alias.out
+++ /dev/null
@@ -1,5 +0,0 @@
-%Error-UNSUPPORTED: t/t_class_extends_alias.v:24:21: Unsupported: TYPEDEF 'foo_t' in 'class extends'
-   24 |   class bar extends foo_t;
-      |                     ^~~~~
-                    ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
-%Error: Exiting due to
diff --git a/test_regress/t/t_class_extends_alias.py b/test_regress/t/t_class_extends_alias.py
index c7d9b21a5..3cc73805c 100755
--- a/test_regress/t/t_class_extends_alias.py
+++ b/test_regress/t/t_class_extends_alias.py
@@ -9,8 +9,10 @@
 
 import vltest_bootstrap
 
-test.scenarios('linter')
+test.scenarios('simulator')
 
-test.lint(fails=True, expect_filename=test.golden_filename)
+test.compile()
+
+test.execute()
 
 test.passes()