Fix extending a class by a typedef (#6679)

docs/CONTRIBUTORS

@@ -273,6 +273,7 @@ Yutetsu TAKATSUKASA
 Yves Mathieu
 Zhanglei Wang
 Zhen Yan
+Zhou Qinnan (Alex)
 Zhou Shen
 Zhouyi Shen
 Zixi Li

src/V3LinkDot.cpp

@@ -5016,6 +5016,23 @@ 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(); // Unwrap typedef to get the underlying type
+                    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()

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.passes()
+test.execute()
+
+test.passes()