Fix variable lifetimes in extern methods (#4414)

src/V3LinkParse.cpp

@@ -296,8 +296,16 @@ private:
             nodep->v3warn(STATICVAR, "Static variable with assignment declaration declared in a "
                                      "loop converted to automatic");
         }
-        if (m_ftaskp && m_ftaskp->classMethod() && nodep->lifetime().isNone()) {
-            nodep->lifetime(VLifetime::AUTOMATIC);
+        if (m_ftaskp) {
+            bool classMethod = m_ftaskp->classMethod();
+            if (!classMethod) {
+                AstClassOrPackageRef* const pkgrefp
+                    = VN_CAST(m_ftaskp->classOrPackagep(), ClassOrPackageRef);
+                if (pkgrefp && VN_IS(pkgrefp->classOrPackagep(), Class)) classMethod = true;
+            }
+            if (classMethod && nodep->lifetime().isNone()) {
+                nodep->lifetime(VLifetime::AUTOMATIC);
+            }
         }
         if (nodep->lifetime().isNone() && nodep->varType() != VVarType::PORT) {
             nodep->lifetime(m_lifetime);

test_regress/t/t_var_extern_method_lifetime.pl

@@ -0,0 +1,23 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2023 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
+
+scenarios(simulator => 1);
+
+compile(
+    verilator_flags2 => ["--exe --main --timing"],
+    make_main => 0,
+    );
+
+execute(
+    check_finished => 1,
+    );
+
+ok(1);
+1;

test_regress/t/t_var_extern_method_lifetime.v

@@ -0,0 +1,35 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2023 by Antmicro Ltd.
+// SPDX-License-Identifier: CC0-1.0
+
+class Foo;
+  int m_v;
+
+  function new(int v);
+    m_v = v;
+  endfunction
+
+  extern task add_in_fork_delayed(int delay, Foo arg);
+endclass
+
+task automatic Foo::add_in_fork_delayed(int delay, Foo arg);
+  fork
+    #delay m_v = m_v + arg.m_v;
+  join_none
+endtask
+
+module t();
+  initial begin
+    Foo foo1, foo2;
+    foo1 = new(1);
+    foo2 = new(2);
+    foo1.add_in_fork_delayed(10, foo2);
+    #20;
+    if (foo1.m_v != 3)
+      $stop;
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule