Add setting to disable mousewheel tab switching.

See #374.

doc/help/settings.asciidoc

@@ -111,6 +111,7 @@
 |<<tabs-indicator-space,indicator-space>>|Spacing between tab edge and indicator.
 |<<tabs-tabs-are-windows,tabs-are-windows>>|Whether to open windows instead of tabs.
 |<<tabs-title-format,title-format>>|The format to use for the tab title. The following placeholders are defined:
+|<<tabs-mousewheel-tab-switching,mousewheel-tab-switching>>|Switch between tabs using the mouse wheel.
 |==============
 
 .Quick reference for section ``storage''
@@ -1031,6 +1032,17 @@ The format to use for the tab title. The following placeholders are defined:
 
 Default: +pass:[{index}: {title}]+
 
+[[tabs-mousewheel-tab-switching]]
+=== mousewheel-tab-switching
+Switch between tabs using the mouse wheel.
+
+Valid values:
+
+ * +true+
+ * +false+
+
+Default: +pass:[true]+
+
 == storage
 Settings related to cache and storage.
 

qutebrowser/config/configdata.py

@@ -522,6 +522,10 @@ def data(readonly=False):
              "* `{index}`: The index of this tab.\n"
              "* `{id}`: The internal tab ID of this tab."),
 
+            ('mousewheel-tab-switching',
+             SettingValue(typ.Bool(), 'true'),
+             "Switch between tabs using the mouse wheel."),
+
             readonly=readonly
         )),
 

qutebrowser/mainwindow/tabwidget.py

@@ -480,6 +480,17 @@ class TabBar(QTabBar):
             new_idx = super().insertTab(idx, icon, '')
         self.set_page_title(new_idx, text)
 
+    def wheelEvent(self, event):
+        """Override wheelEvent to make the action configurable."""
+        if config.get('tabs', 'mousewheel-tab-switching'):
+            super().wheelEvent(event)
+        else:
+            tabbed_browser = objreg.get('tabbed-browser', scope='window',
+                                        window=self._win_id)
+            focused_tab = tabbed_browser.currentWidget()
+            if focused_tab is not None:
+                focused_tab.wheelEvent(event)
+
 
 class TabBarStyle(QCommonStyle):