Fix updating fonts when fonts.monospace is changed

Fixes #2973

qutebrowser/config/configinit.py

@@ -75,6 +75,7 @@ def early_init(args):
             message.error("set: {} - {}".format(e.__class__.__name__, e))
 
     configtypes.Font.monospace_fonts = config.val.fonts.monospace
+    config.instance.changed.connect(_update_monospace_fonts)
 
     _init_envvars()
 
@@ -94,6 +95,21 @@ def _init_envvars():
         os.environ.pop('QT_WAYLAND_DISABLE_WINDOWDECORATION', None)
 
 
+@config.change_filter('fonts.monospace', function=True)
+def _update_monospace_fonts():
+    """Update all fonts if fonts.monospace was set."""
+    configtypes.Font.monospace_fonts = config.val.fonts.monospace
+    for name, opt in configdata.DATA.items():
+        if name == 'fonts.monospace':
+            continue
+        elif not isinstance(opt.typ, configtypes.Font):
+            continue
+        elif not config.instance.get_obj(name).endswith(' monospace'):
+            continue
+
+        config.instance.changed.emit(name)
+
+
 def get_backend(args):
     """Find out what backend to use based on available libraries."""
     str_to_backend = {

tests/unit/config/test_configinit.py

@@ -211,6 +211,22 @@ class TestEarlyInit:
         assert config.instance.get('fonts.keyhint') == '8pt "Comic Sans MS"'
         assert config.instance.get('fonts.tabs').family() == 'Comic Sans MS'
 
+    def test_monospace_fonts_later(self, init_patch, args):
+        """Ensure setting fonts.monospace after init works properly.
+
+        See https://github.com/qutebrowser/qutebrowser/issues/2973
+        """
+        configinit.early_init(args)
+        changed_options = []
+        config.instance.changed.connect(changed_options.append)
+
+        config.instance.set_obj('fonts.monospace', '"Comic Sans MS"')
+
+        assert 'fonts.keyhint' in changed_options
+        assert config.instance.get('fonts.keyhint') == '8pt "Comic Sans MS"'
+        assert 'fonts.tabs' in changed_options
+        assert config.instance.get('fonts.tabs').family() == 'Comic Sans MS'
+
     def test_force_software_rendering(self, monkeypatch, config_stub):
         """Setting force_software_rendering should set the environment var."""
         envvar = 'QT_XCB_FORCE_SOFTWARE_OPENGL'