[meld] Rework linkmap scroll handling to not require the parent MeldDoc

[Kai Willadsen <kaiw src gnome org>]

commit 90ff3f3758f7f7d5934248b341e501b3cfa9a9cf
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sat Nov 18 06:00:34 2017 +1000

    Rework linkmap scroll handling to not require the parent MeldDoc
    
    Keeping the parent MeldDoc is an annoying requirement, and the backref
    shows up when trying to track down reference leaks. Having the parent
    documents be responsible for hooking in the scroll-event signal handler,
    as in this patch, is both a better separation and less pain.

 data/ui/dirdiff.ui  |    2 ++
 data/ui/filediff.ui |    2 ++
 meld/dirdiff.py     |    6 +++---
 meld/filediff.py    |    3 +++
 meld/linkmap.py     |   14 --------------
 5 files changed, 10 insertions(+), 17 deletions(-)
---
diff --git a/data/ui/dirdiff.ui b/data/ui/dirdiff.ui
index e60c117..e60b335 100644
--- a/data/ui/dirdiff.ui
+++ b/data/ui/dirdiff.ui
@@ -263,6 +263,7 @@
                 <property name="can_focus">False</property>
                 <property name="events">GDK_SCROLL_MASK</property>
                 <property name="vexpand">True</property>
+                <signal name="scroll-event" handler="on_linkmap_scroll_event" swapped="no"/>
               </object>
               <packing>
                 <property name="left_attach">4</property>
@@ -321,6 +322,7 @@
                 <property name="can_focus">False</property>
                 <property name="events">GDK_SCROLL_MASK</property>
                 <property name="vexpand">True</property>
+                <signal name="scroll-event" handler="on_linkmap_scroll_event" swapped="no"/>
               </object>
               <packing>
                 <property name="left_attach">2</property>
diff --git a/data/ui/filediff.ui b/data/ui/filediff.ui
index ebe8f75..dbba760 100644
--- a/data/ui/filediff.ui
+++ b/data/ui/filediff.ui
@@ -719,6 +719,7 @@
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
                 <property name="events">GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK | GDK_KEY_PRESS_MASK 
| GDK_KEY_RELEASE_MASK | GDK_SCROLL_MASK</property>
+                <signal name="scroll-event" handler="on_linkmap_scroll_event" swapped="no"/>
               </object>
               <packing>
                 <property name="left_attach">2</property>
@@ -775,6 +776,7 @@
                 <property name="visible">True</property>
                 <property name="can_focus">False</property>
                 <property name="events">GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK | GDK_KEY_PRESS_MASK 
| GDK_KEY_RELEASE_MASK | GDK_SCROLL_MASK</property>
+                <signal name="scroll-event" handler="on_linkmap_scroll_event" swapped="no"/>
               </object>
               <packing>
                 <property name="left_attach">4</property>
diff --git a/meld/dirdiff.py b/meld/dirdiff.py
index 68f95d4..eb2c26d 100644
--- a/meld/dirdiff.py
+++ b/meld/dirdiff.py
@@ -1467,9 +1467,6 @@ class DirDiff(melddoc.MeldDoc, gnomeglade.Component):
                 idx = 1 if i else 0
                 w.setup(scroll, self.get_state_traversal(idx))
 
-            for w in self.linkmap:
-                w.associate(self)
-
             for widget in (
                     self.vbox[:n] + self.file_toolbar[:n] + self.diffmap[:n] +
                     self.linkmap[:n - 1] + self.dummy_toolbar_linkmap[:n - 1]):
@@ -1559,6 +1556,9 @@ class DirDiff(melddoc.MeldDoc, gnomeglade.Component):
         self._update_diffmaps()
         self.force_cursor_recalculate = True
 
+    def on_linkmap_scroll_event(self, linkmap, event):
+        self.next_diff(event.direction)
+
     def next_diff(self, direction):
         if self.focus_pane:
             pane = self.treeview.index(self.focus_pane)
diff --git a/meld/filediff.py b/meld/filediff.py
index 5a571ec..f0551e6 100644
--- a/meld/filediff.py
+++ b/meld/filediff.py
@@ -491,6 +491,9 @@ class FileDiff(melddoc.MeldDoc, gnomeglade.Component):
         self.textview[pane].scroll_to_mark(
             buf.get_insert(), tolerance, True, 0.5, 0.5)
 
+    def on_linkmap_scroll_event(self, linkmap, event):
+        self.next_diff(event.direction)
+
     def next_diff(self, direction, centered=False):
         target = (self.cursor.next if direction == Gdk.ScrollDirection.DOWN
                   else self.cursor.prev)
diff --git a/meld/linkmap.py b/meld/linkmap.py
index 15e1dff..8931e73 100644
--- a/meld/linkmap.py
+++ b/meld/linkmap.py
@@ -131,9 +131,6 @@ class LinkMap(Gtk.DrawingArea):
             Gdk.cairo_set_source_rgba(context, self.line_colors[c[0]])
             context.stroke()
 
-    def do_scroll_event(self, event):
-        self.filediff.next_diff(event.direction)
-
 
 LinkMap.set_css_name("link-map")
 
@@ -141,14 +138,3 @@ LinkMap.set_css_name("link-map")
 class ScrollLinkMap(Gtk.DrawingArea):
 
     __gtype_name__ = "ScrollLinkMap"
-
-    def __init__(self):
-        self.melddoc = None
-
-    def associate(self, melddoc):
-        self.melddoc = melddoc
-
-    def do_scroll_event(self, event):
-        if not self.melddoc:
-            return
-        self.melddoc.next_diff(event.direction)