[meld] Improve state skipping logic, and avoid order comparisons between types

[Kai Willadsen <kaiw src gnome org>]

commit c8a2c1b5f00528b387b7f8543f306265d8bd08d3
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sat Oct 27 13:04:02 2012 +1000

    Improve state skipping logic, and avoid order comparisons between types
    
    There were problems with our previous state-calculation skipping logic
    where calculation was not correctly skipped in cases where the previous
    and/or next differences were None. In particular, this would cause
    problems in Python 3, where comparisons between unequal types are not
    allowed.

 meld/dirdiff.py |   36 ++++++++++++++++++++++++++----------
 meld/vcview.py  |   35 +++++++++++++++++++++++++----------
 2 files changed, 51 insertions(+), 20 deletions(-)
---
diff --git a/meld/dirdiff.py b/meld/dirdiff.py
index 847415b..66c5723 100644
--- a/meld/dirdiff.py
+++ b/meld/dirdiff.py
@@ -630,6 +630,7 @@ class DirDiff(melddoc.MeldDoc, gnomeglade.Component):
             self.treeview[0].expand_to_path(path)
         yield _("[%s] Done") % self.label_text
         self.actiongroup.get_action("Hide").set_sensitive(True)
+        self.scheduler.add_task(self.on_treeview_cursor_changed)
 
     def _show_tree_wide_errors(self, invalid_filenames, shadowed_entries):
         header = _("Multiple errors occurred while scanning this folder")
@@ -816,6 +817,12 @@ class DirDiff(melddoc.MeldDoc, gnomeglade.Component):
         cursor_path, cursor_col = self.treeview[pane].get_cursor()
         if not cursor_path:
             self.emit("next-diff-changed", False, False)
+            self.current_path = cursor_path
+            return
+
+        # If invoked directly rather than through a callback, we always check
+        if not args:
+            skip = False
         else:
             try:
                 old_cursor = self.model.get_iter(self.current_path)
@@ -823,17 +830,26 @@ class DirDiff(melddoc.MeldDoc, gnomeglade.Component):
                 # An invalid path gives ValueError; None gives a TypeError
                 skip = False
             else:
+                # We can skip recalculation if the new cursor is between
+                # the previous/next bounds, and we weren't on a changed row
                 state = self.model.get_state(old_cursor, 0)
-                # We can skip recalculation if the new cursor is between the
-                # previous/next bounds, and we weren't on a changed row
-                skip = state in (tree.STATE_NORMAL, tree.STATE_EMPTY) and \
-                       self.prev_path < cursor_path < self.next_path
-
-            if not skip:
-                prev, next = self.model._find_next_prev_diff(cursor_path)
-                self.prev_path, self.next_path = prev, next
-                have_next_diffs = (prev is not None, next is not None)
-                self.emit("next-diff-changed", *have_next_diffs)
+                if state not in (tree.STATE_NORMAL, tree.STATE_EMPTY):
+                    skip = False
+                else:
+                    if self.prev_path is None and self.next_path is None:
+                        skip = True
+                    elif self.prev_path is None:
+                        skip = cursor_path < self.next_path
+                    elif self.next_path is None:
+                        skip = self.prev_path < cursor_path
+                    else:
+                        skip = self.prev_path < cursor_path < self.next_path
+
+        if not skip:
+            prev, next = self.model._find_next_prev_diff(cursor_path)
+            self.prev_path, self.next_path = prev, next
+            have_next_diffs = (prev is not None, next is not None)
+            self.emit("next-diff-changed", *have_next_diffs)
         self.current_path = cursor_path
 
         paths = self._get_selected_paths(pane)
diff --git a/meld/vcview.py b/meld/vcview.py
index 31ef142..486ee99 100644
--- a/meld/vcview.py
+++ b/meld/vcview.py
@@ -714,6 +714,12 @@ class VcView(melddoc.MeldDoc, gnomeglade.Component):
         cursor_path, cursor_col = self.treeview.get_cursor()
         if not cursor_path:
             self.emit("next-diff-changed", False, False)
+            self.current_path = cursor_path
+            return
+
+        # If invoked directly rather than through a callback, we always check
+        if not args:
+            skip = False
         else:
             try:
                 old_cursor = self.model.get_iter(self.current_path)
@@ -721,17 +727,26 @@ class VcView(melddoc.MeldDoc, gnomeglade.Component):
                 # An invalid path gives ValueError; None gives a TypeError
                 skip = False
             else:
+                # We can skip recalculation if the new cursor is between
+                # the previous/next bounds, and we weren't on a changed row
                 state = self.model.get_state(old_cursor, 0)
-                # We can skip recalculation if the new cursor is between the
-                # previous/next bounds, and we weren't on a changed row
-                skip = state in (tree.STATE_NORMAL, tree.STATE_EMPTY) and \
-                       self.prev_path < cursor_path < self.next_path
-
-            if not skip:
-                prev, next = self.model._find_next_prev_diff(cursor_path)
-                self.prev_path, self.next_path = prev, next
-                have_next_diffs = (prev is not None, next is not None)
-                self.emit("next-diff-changed", *have_next_diffs)
+                if state not in (tree.STATE_NORMAL, tree.STATE_EMPTY):
+                    skip = False
+                else:
+                    if self.prev_path is None and self.next_path is None:
+                        skip = True
+                    elif self.prev_path is None:
+                        skip = cursor_path < self.next_path
+                    elif self.next_path is None:
+                        skip = self.prev_path < cursor_path
+                    else:
+                        skip = self.prev_path < cursor_path < self.next_path
+
+        if not skip:
+            prev, next = self.model._find_next_prev_diff(cursor_path)
+            self.prev_path, self.next_path = prev, next
+            have_next_diffs = (prev is not None, next is not None)
+            self.emit("next-diff-changed", *have_next_diffs)
         self.current_path = cursor_path
 
     def next_diff(self, direction):