Use main editor for loop-range undo/redo - fix crash

While CueEditor is-a HistoryOwner, session specific
changes such as Location don't belong in EditingContext.

This fixes a heap-use-after-free crash since MementoCommand
was free()ed twice. Once via ARDOUR::Location::~Location
and earlier due to direct Destructible::drop_references
from the History.

This partially reverts 04a8fb1eb6

gtk2_ardour/cue_editor.cc

@@ -35,6 +35,7 @@
 #include "cue_editor.h"
 #include "editor_drag.h"
 #include "gui_thread.h"
+#include "public_editor.h"
 #include "timers.h"
 #include "ui_config.h"
 
@@ -562,7 +563,7 @@ CueEditor::loop_button_press (GdkEventButton* ev)
 	if (_session->get_play_loop()) {
 		_session->request_play_loop (false);
 	} else {
-		set_loop_range (_region->position(), _region->end(), _("loop region"));
+		PublicEditor::instance().set_loop_range (_region->position(), _region->end(), _("loop region"));
 		_session->request_play_loop (true);
 	}
 

gtk2_ardour/editing_context.cc

@@ -3475,40 +3475,6 @@ EditingContext::transport_loop_location()
 	}
 }
 
-void
-EditingContext::set_loop_range (timepos_t const & start, timepos_t const & end, string cmd)
-{
-	EC_LOCAL_TEMPO_SCOPE;
-
-	if (!_session) {
-		return;
-	}
-	if (_session->get_play_loop () && _session->actively_recording ()) {
-		return;
-	}
-
-	begin_reversible_command (cmd);
-
-	Location* tll;
-
-	if ((tll = transport_loop_location()) == 0) {
-		Location* loc = new Location (*_session, start, end, _("Loop"),  Location::IsAutoLoop);
-		XMLNode &before = _session->locations()->get_state();
-		_session->locations()->add (loc, true);
-		_session->set_auto_loop_location (loc);
-		XMLNode &after = _session->locations()->get_state();
-		add_command (new MementoCommand<Locations>(*(_session->locations()), &before, &after));
-	} else {
-		XMLNode &before = tll->get_state();
-		tll->set_hidden (false, this);
-		tll->set (start, end);
-		XMLNode &after = tll->get_state();
-		add_command (new MementoCommand<Location>(*tll, &before, &after));
-	}
-
-	commit_reversible_command ();
-}
-
 bool
 EditingContext::allow_trim_cursors () const
 {

gtk2_ardour/editing_context.h

@@ -481,8 +481,6 @@ class EditingContext : public ARDOUR::SessionHandlePtr, public AxisViewProvider,
 
 	virtual void update_grid ();
 
-	void set_loop_range (Temporal::timepos_t const & start, Temporal::timepos_t const & end, std::string cmd);
-
 	virtual bool allow_trim_cursors () const;
 	virtual void make_a_region() {}
 

gtk2_ardour/editor.cc

@@ -4072,6 +4072,41 @@ Editor::_get_preferred_edit_position (EditIgnoreOption ignore, bool from_context
 	return where;
 }
 
+void
+Editor::set_loop_range (timepos_t const & start, timepos_t const & end, string cmd)
+{
+	if (!_session) {
+		return;
+	}
+	if (_session->get_play_loop () && _session->actively_recording ()) {
+		return;
+	}
+
+	begin_reversible_command (cmd);
+
+	Location* tll;
+
+	if ((tll = transport_loop_location()) == 0) {
+		Location* loc = new Location (*_session, start, end, _("Loop"),  Location::IsAutoLoop);
+		XMLNode &before = _session->locations()->get_state();
+		_session->locations()->add (loc, true);
+		_session->set_auto_loop_location (loc);
+		XMLNode &after = _session->locations()->get_state();
+		add_command (new MementoCommand<Locations>(*(_session->locations()), &before, &after));
+	} else if (tll->start() != start || tll->end () != end){
+		XMLNode &before = tll->get_state();
+		tll->set_hidden (false, this);
+		tll->set (start, end);
+		XMLNode &after = tll->get_state();
+		add_command (new MementoCommand<Location>(*tll, &before, &after));
+	} else {
+		abort_reversible_command ();
+		return;
+	}
+
+	commit_reversible_command ();
+}
+
 void
 Editor::set_punch_range (timepos_t const & start, timepos_t const & end, string cmd)
 {

gtk2_ardour/editor.h

@@ -1413,6 +1413,7 @@ private:
 
 	void set_loop_from_region (bool play);
 
+	void set_loop_range (Temporal::timepos_t const & start, Temporal::timepos_t const & end, std::string cmd);
 	void set_punch_range (Temporal::timepos_t const & start, Temporal::timepos_t const & end, std::string cmd);
 
 	void add_tempo_from_playhead_cursor ();

gtk2_ardour/public_editor.h

@@ -192,6 +192,7 @@ public:
 	}
 	virtual void add_location_mark_with_flag (Temporal::timepos_t const & where, ARDOUR::Location::Flags, int32_t cue_id) = 0;
 	virtual void remove_tracks () = 0;
+	virtual void set_loop_range (Temporal::timepos_t const & start, Temporal::timepos_t const & end, std::string cmd) = 0;
 	virtual void set_punch_range (Temporal::timepos_t const & start, Temporal::timepos_t const & end, std::string cmd) = 0;
 
 	void jump_forward_to_mark () {