[libsigc++2] slot_rep::disconnect(): Remove a comment, add a test

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 54b5c013552e753fad02c879ace7d0f7f91f33b6
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Sun Oct 11 15:12:10 2015 +0200

    slot_rep::disconnect(): Remove a comment, add a test
    
    * sigc++/functors/slot_base.cc: Remove a TODO comment at slot_rep::disconnect().
    * tests/test_slot_disconnect.cc: Add a test that assigns an empty slot.

 sigc++/functors/slot_base.cc  |   19 +++++++++----------
 tests/test_slot_disconnect.cc |    5 ++++-
 2 files changed, 13 insertions(+), 11 deletions(-)
---
diff --git a/sigc++/functors/slot_base.cc b/sigc++/functors/slot_base.cc
index 2bc0d40..88a91f9 100644
--- a/sigc++/functors/slot_base.cc
+++ b/sigc++/functors/slot_base.cc
@@ -55,23 +55,22 @@ void slot_rep::operator delete(void* p)
 }
 #endif
 
-//TODO: When we can break API: Is it necessary to invalidate the slot here?
-// If the parent misbehaves, when the slot is not invalidated, isn't that
-// a problem that should be fixed in the parent?
-// See discussion in https://bugzilla.gnome.org/show_bug.cgi?id=738602
 void slot_rep::disconnect()
 {
+  // Invalidate the slot.
+  // _Must_ be done here because parent_ might defer the actual
+  // destruction of the slot_rep and try to invoke it before that point.
+  // Must be done also for a slot without a parent, according to
+  // https://bugzilla.gnome.org/show_bug.cgi?id=311057
+  // See also https://bugzilla.gnome.org/show_bug.cgi?id=738602
+  call_ = nullptr;
+
   if (parent_)
   {
-    call_ = nullptr;          // Invalidate the slot.
-                        // _Must_ be done here because parent_ might defer the actual
-                        // destruction of the slot_rep and try to invoke it before that point.
     auto data_ = parent_;
-    parent_ = nullptr;        // Just a precaution.
+    parent_ = nullptr;  // Just a precaution.
     (cleanup_)(data_);  // Notify the parent (might lead to destruction of this!).
   }
-  else
-    call_ = nullptr;
 }
 
 //static
diff --git a/tests/test_slot_disconnect.cc b/tests/test_slot_disconnect.cc
index 13d42e0..a1d6834 100644
--- a/tests/test_slot_disconnect.cc
+++ b/tests/test_slot_disconnect.cc
@@ -1,4 +1,3 @@
-// -*- c++ -*-
 /* Copyright 2005, The libsigc++ Development Team
  *  Assigned to public domain.  Use as you wish without restriction.
  */
@@ -45,5 +44,9 @@ int main(int argc, char* argv[])
   theSlot();
   util->check_result(result_stream, "Bar");
 
+  theSlot = sigc::slot<void>(); // Assign an empty slot.
+  theSlot();
+  util->check_result(result_stream, "");
+
   return util->get_result_and_delete_instance() ? EXIT_SUCCESS : EXIT_FAILURE;
 }