Only update tab/window title on scroll if needed

This way, if {scroll_pos} is not in the window/tab title template,
we don't redraw anything unnecessarily.

See #2233

qutebrowser/mainwindow/tabbedbrowser.py

@@ -173,8 +173,18 @@ class TabbedBrowser(tabwidget.TabWidget):
                 widgets.append(widget)
         return widgets
 
-    def _update_window_title(self):
-        """Change the window title to match the current tab."""
+    def _update_window_title(self, field=None):
+        """Change the window title to match the current tab.
+
+        Args:
+            idx: The tab index to update.
+            field: A field name which was updated. If given, the title
+                   is only set if the given field is in the template.
+        """
+        title_format = config.val.window.title_format
+        if field is not None and ('{' + field + '}') not in title_format:
+            return
+
         idx = self.currentIndex()
         if idx == -1:
             # (e.g. last tab removed)
@@ -183,7 +193,6 @@ class TabbedBrowser(tabwidget.TabWidget):
         fields = self.get_tab_fields(idx)
         fields['id'] = self._win_id
 
-        title_format = config.val.window.title_format
         title = title_format.format(**fields)
         self.window().setWindowTitle(title)
 
@@ -696,8 +705,8 @@ class TabbedBrowser(tabwidget.TabWidget):
             log.webview.debug("Not updating scroll position because index is "
                               "-1")
             return
-        self._update_window_title()
-        self._update_tab_title(idx)
+        self._update_window_title('scroll_pos')
+        self._update_tab_title(idx, 'scroll_pos')
 
     def _on_renderer_process_terminated(self, tab, status, code):
         """Show an error when a renderer process terminated."""

qutebrowser/mainwindow/tabwidget.py

@@ -121,21 +121,29 @@ class TabWidget(QTabWidget):
         """Get the tab title user data."""
         return self.tabBar().page_title(idx)
 
-    def _update_tab_title(self, idx):
-        """Update the tab text for the given tab."""
+    def _update_tab_title(self, idx, field=None):
+        """Update the tab text for the given tab.
+
+        Args:
+            idx: The tab index to update.
+            field: A field name which was updated. If given, the title
+                   is only set if the given field is in the template.
+        """
         tab = self.widget(idx)
+        if tab.data.pinned:
+            fmt = config.val.tabs.title.format_pinned
+        else:
+            fmt = config.val.tabs.title.format
+
+        if (field is not None and
+                (fmt is None or ('{' + field + '}') not in fmt)):
+            return
+
         fields = self.get_tab_fields(idx)
         fields['title'] = fields['title'].replace('&', '&&')
         fields['index'] = idx + 1
 
-        fmt = config.val.tabs.title.format
-        fmt_pinned = config.val.tabs.title.format_pinned
-
-        if tab.data.pinned:
-            title = '' if fmt_pinned is None else fmt_pinned.format(**fields)
-        else:
-            title = '' if fmt is None else fmt.format(**fields)
-
+        title = '' if fmt is None else fmt.format(**fields)
         self.tabBar().setTabText(idx, title)
 
     def get_tab_fields(self, idx):