Fix extern function that returns parametrized class (#4924).

Changes

@@ -41,6 +41,7 @@ Verilator 5.043 devel
 * Optimize $past delayed variable reuse (#6689). [Geza Lore, Fractile Ltd.]
 * Optimize combinational loops through sign extension (#6724). [Geza Lore]
 * Optimize trace initialization code size (#6749). [Geza Lore]
+* Fix extern function that returns parametrized class (#4924).
 * Fix expression short circuiting (#6483). [Todd Strader]
 * Fix expression coverage of system calls (#6592). [Todd Strader]
 * Fix `--timing` with `--x-initial-edge` (#6603) (#6631). [Krzysztof Bieganski, Antmicro Ltd.]

include/verilatedos.h

@@ -261,6 +261,16 @@
         VL_DANGLING(var); \
     } while (false)
 
+/// As with VL_DO_DANGLING, but two variables dangle.
+#define VL_DO_DANGLING2(stmt, var, var2) \
+    do { \
+        do { \
+            stmt; \
+        } while (false); \
+        VL_DANGLING(var); \
+        VL_DANGLING(var2); \
+    } while (false)
+
 /// Perform an e.g. delete, then set variable to nullptr as a requirement
 #define VL_DO_CLEAR(stmt, stmt2) \
     do { \

src/V3LinkDot.cpp

@@ -966,18 +966,17 @@ class LinkDotFindVisitor final : public VNVisitor {
 
     void moveExternFuncDecl(AstNodeFTask* nodep, AstClass* classp) {
         // Move an 'extern function|task' to inside a class or, from an outer to inner-class
-        if (!nodep->isExternDef()) {
+        if (nodep->isExternDef()) return;
-            // Move it to proper spot under the target class
+        // Move it to proper spot under the target class
-            nodep->unlinkFrBack();
+        nodep->unlinkFrBack();
-            classp->addStmtsp(nodep);
+        classp->addStmtsp(nodep);
-            nodep->isExternDef(true);  // So we check there's a matching extern
+        nodep->isExternDef(true);  // So we check there's a matching extern
-            nodep->classOrPackagep()->unlinkFrBack()->deleteTree();
+        nodep->classOrPackagep()->unlinkFrBack()->deleteTree();
-            // Any "Type::" reference in the function's IO are really "MovedToClass::" references
+        // Any "Type::" reference in the function's IO are really "MovedToClass::" references
-            if (nodep->fvarp()) moveExternFuncDeclRefs(nodep->fvarp(), classp);
+        if (nodep->fvarp()) moveExternFuncDeclRefs(nodep->fvarp(), classp);
-            for (AstNode* stmtp = nodep->stmtsp(); stmtp; stmtp = stmtp->nextp()) {
+        for (AstNode* stmtp = nodep->stmtsp(); stmtp; stmtp = stmtp->nextp()) {
-                if (AstVar* const portp = VN_CAST(stmtp, Var)) {
+            if (AstVar* const portp = VN_CAST(stmtp, Var)) {
-                    if (portp->isIO()) moveExternFuncDeclRefs(portp, classp);
+                if (portp->isIO()) moveExternFuncDeclRefs(portp, classp);
-                }
             }
         }
     }
@@ -985,7 +984,14 @@ class LinkDotFindVisitor final : public VNVisitor {
         nodep->foreach([this, classp](AstClassOrPackageRef* refp) {  //
             if (refp->name() == classp->name() && !refp->paramsp()) {
                 UINFO(9, "Cleaning up external function type for class " << refp);
-                pushDeletep(refp->unlinkFrBack());
+                AstDot* const dotp = VN_CAST(refp->backp(), Dot);
+                if (dotp && dotp->lhsp() == refp) {
+                    // If had DOT(CLASSREF this, ...) the DOT can go away
+                    dotp->replaceWith(dotp->rhsp()->unlinkFrBack());
+                    VL_DO_DANGLING2(pushDeletep(dotp), dotp, refp);
+                } else {
+                    VL_DO_DANGLING(pushDeletep(refp->unlinkFrBack()), refp);
+                }
             }
         });
     }

test_regress/t/t_class_extern2.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2024 by Wilson Snyder. 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-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile()
+
+test.execute()
+
+test.passes()

test_regress/t/t_class_extern2.v

@@ -0,0 +1,54 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+class One #(
+    type VALUE_T = int unsigned
+);
+  typedef One#(VALUE_T) self_t;
+  VALUE_T value;
+  extern static function self_t create(VALUE_T value);
+endclass
+
+class Two #(
+    type VALUE_T = int unsigned
+);
+  VALUE_T value;
+  extern static function Two#(VALUE_T) create(VALUE_T value);
+`ifdef NEVER
+  // works ok if put function directly here
+  static function Two#(VALUE_T) create(VALUE_T value);
+    Two #(VALUE_T) obj = new();
+    obj.value = value;
+    return obj;
+  endfunction
+`endif
+endclass
+
+function One::self_t One::create(VALUE_T value);
+  One #(VALUE_T) obj = new();
+  obj.value = value;
+  return obj;
+endfunction
+
+function Two#(Two::VALUE_T) Two::create(VALUE_T value);
+  Two #(VALUE_T) obj = new();
+  obj.value = value;
+  return obj;
+endfunction
+
+module t;
+  initial begin
+    One #(string) one;
+    Two #(string) two;
+    one = One#(string)::create("one");
+    two = Two#(string)::create("two");
+    if (one.value !== "one") $stop;
+    if (two.value !== "two") $stop;
+
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule