Fix: Empty compare target

Fixes #560

Setting compare target to `origin` may cause a `None` target to be
applied. GitGutter no longer knows that to compare against and raises
exceptions.

This commit fixes `on_branch_name()` to set a new compare target if the
given value is empty and ensures the handler to use sane fallback values
in case compare target values are empty.

modules/compare.py

@@ -174,9 +174,10 @@ def set_against_origin(git_gutter, **kwargs):
             by the GitGutterCommand object.
     """
     def on_branch_name(status):
-        if not status or not status.get('remote'):
-            sublime.message_dialog('Current branch has not tracking remote!')
-        git_gutter.git_handler.set_compare_against(status.get('remote'), True)
+        remote = status.get('remote') if status else None
+        if remote:
+            git_gutter.git_handler.set_compare_against(remote, True)
+        sublime.message_dialog('Current branch has no tracking remote!')
 
     git_gutter.git_handler.git_branch_status().then(on_branch_name)
 

modules/handler.py

@@ -220,10 +220,11 @@ def get_compare_against(self):
                 The reference to compare the view against.
         """
         # Interactively specified compare target overrides settings.
-        if self._git_tree in self._compare_against_mapping:
-            return self._compare_against_mapping[self._git_tree]
-        # Project settings and Preferences override plugin settings if set.
-        return self.settings.get('compare_against', 'HEAD')
+        result = self._compare_against_mapping.get(self._git_tree)
+        if not result:
+            # Project settings and Preferences override plugin settings if set.
+            result = self.settings.get('compare_against', 'HEAD')
+        return result
 
     def set_compare_against(self, compare_against, refresh=False):
         """Apply a new branch/commit/tag string the view is compared to.
@@ -239,6 +240,8 @@ def set_compare_against(self, compare_against, refresh=False):
                 from 'git show-ref' to compare the view against
             refresh (bool): True to force git diff and update GUI
         """
+        if not compare_against:
+            return
         self._compare_against_mapping[self._git_tree] = compare_against
         # force refresh if live_mode and focus_change_mode are disabled
         refresh |= (not self.settings.get('live_mode') and