[libsigcplusplus/libsigc++-2-10] slot_base::set_parent(): Create a dummy slot_rep if necessary

[Kjell Ahlstedt <kjellahl src gnome org>]

commit a0089c47b0942cf889aaf45e5a5348b6fac644c3
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Nov 9 09:13:28 2017 +0100

    slot_base::set_parent(): Create a dummy slot_rep if necessary
    
    set_parent() must always store the supplied parent pointer and cleanup
    function pointer, or else there may be a memory leak. The pointers are
    stored in slot_rep. Bug 167714

 sigc++/functors/slot_base.cc |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)
---
diff --git a/sigc++/functors/slot_base.cc b/sigc++/functors/slot_base.cc
index 1b8285a..84b9df7 100644
--- a/sigc++/functors/slot_base.cc
+++ b/sigc++/functors/slot_base.cc
@@ -36,6 +36,14 @@ struct destroy_notify_struct
 
   bool deleted_;
 };
+
+// Used by slot_base::set_parent() when a slot_base without a rep_ is assigned a parent.
+class dummy_slot_rep : public sigc::internal::slot_rep
+{
+public:
+  dummy_slot_rep() : slot_rep(nullptr, nullptr, &clone) {}
+  static void* clone(void*) { return new dummy_slot_rep(); }
+};
 } // anonymous namespace
 
 namespace sigc
@@ -263,8 +271,9 @@ slot_base& slot_base::operator=(slot_base&& src)
 
 void slot_base::set_parent(void* parent, void* (*cleanup)(void*)) const noexcept
 {
-  if (rep_)
-    rep_->set_parent(parent, cleanup);
+  if (!rep_)
+    rep_ = new dummy_slot_rep();
+  rep_->set_parent(parent, cleanup);
 }
 
 void slot_base::add_destroy_notify_callback(void* data, func_destroy_notify func) const