Switch a couple more traversals to child first

I think when removing nodes it's less work to remove leaves first, so that
children don't have to be reparented. We also don't need to save everything to
a list. I don't know what the difference out of POST and POST_R, maybe if you
remove the last sibling first it's less work? Not sure.

Also take care of a fixme comment which is fixed (the comment it refers to is
still there, but add_undo_entry is no longer modifying the tree).

2 files changed, 9 insertions, 6 deletions

diff --git a/qutebrowser/browser/commands.py b/qutebrowser/browser/commands.py
index aa720a747..caba596c3 100644
--- a/qutebrowser/browser/commands.py
+++ b/qutebrowser/browser/commands.py
@@ -522,7 +522,10 @@ class CommandDispatcher:
         # third pass: remove tabs from old window, children first this time to
         # avoid having to re-parent things when traversing.
         if not keep:
-            for node in reversed(traversed):
+            for node in self._current_widget().node.traverse(
+                notree.TraverseOrder.POST_R,
+                render_collapsed=False,
+            ):
                 self._tabbed_browser.close_tab(node.value,
                                                add_undo=False,
                                                transfer=True)
diff --git a/qutebrowser/mainwindow/treetabbedbrowser.py b/qutebrowser/mainwindow/treetabbedbrowser.py
index eacc9f4c3..2fe6d4c84 100644
--- a/qutebrowser/mainwindow/treetabbedbrowser.py
+++ b/qutebrowser/mainwindow/treetabbedbrowser.py
@@ -81,22 +81,22 @@ class TreeTabbedBrowser(TabbedBrowser):
 
     def _remove_tab(self, tab, *, add_undo=True, new_undo=True, crashed=False):
         """Handle children positioning after a tab is removed."""
-        node = tab.node
-        # FIXME after the fixme in _add_undo_entry is resolved, no need
-        # to save descendents
-        descendents = tuple(node.traverse(render_collapsed=True))
 
         if not tab.url().isEmpty() and tab.url().isValid() and add_undo:
             idx = self.widget.indexOf(tab)
             self._add_undo_entry(tab, idx, new_undo)
 
+        node = tab.node
         parent = node.parent
 
         if node.collapsed:
             # Collapsed nodes have already been removed from the TabWidget so
             # we can't ask super() to dispose of them and need to do it
             # ourselves.
-            for descendent in descendents:
+            for descendent in node.traverse(
+                order=notree.TraverseOrder.POST_R,
+                render_collapsed=True
+            ):
                 descendent.parent = None
                 descendent_tab = descendent.value
                 descendent_tab.private_api.shutdown()