Make dump_userconfig work correctly

TODO

@@ -1,7 +1,6 @@
 Bugs
 ====
 
-dump_userconfig dumps everything for ValueList sections
 All kind of FIXMEs
 Weird font rendering
     https://bugreports.qt-project.org/browse/QTBUG-20973

qutebrowser/config/config.py

@@ -346,17 +346,10 @@ class Config(QObject):
         # FIXME adopt this for layering
         lines = []
         for secname, section in self.config.items():
-            changed_opts = []
+            changed = section.dump_userconfig()
-            for optname, option in section.items():
+            if changed:
-                if (option.values['temp'] is not None and
-                        option.values['temp'] != option.values['default'] or
-                    option.values['conf'] is not None and
-                        option.values['conf'] != option.values['default']):
-                    keyval = '{} = {}'.format(optname, option)  # FIXME layer?
-                    changed_opts.append(keyval)
-            if changed_opts:
                 lines.append('[{}]'.format(secname))
-                lines += changed_opts
+                lines += ['{} = {}'.format(k, v) for k, v in changed]
         return '\n'.join(lines)
 
     def optionxform(self, val):

qutebrowser/config/sections.py

@@ -93,6 +93,14 @@ class Section:
         """Initialize the values from a configparser section."""
         raise NotImplementedError
 
+    def dump_userconfig(self):
+        """Dump the part of the config which was changed by the user.
+
+        Return:
+            A list of (key, valuestr) tuples.
+        """
+        raise NotImplementedError
+
 
 class KeyValue(Section):
 
@@ -124,6 +132,17 @@ class KeyValue(Section):
             logging.debug("'{}' = '{}'".format(k, v))
             self.values[k].setv('conf', v)
 
+    def dump_userconfig(self):
+        changed = []
+        for k, v in self.items():
+            if (v.values['temp'] is not None and
+                    v.values['temp'] != v.values['default']):
+                changed.append((k, v.values['temp']))
+            elif (v.values['conf'] is not None and
+                    v.values['conf'] != v.values['default']):
+                changed.append((k, v.values['conf']))
+        return changed
+
 
 class ValueList(Section):
 
@@ -165,14 +184,6 @@ class ValueList(Section):
                                self.layers['default'])
 
     def setv(self, layer, key, value):
-        """Set the value on a layer.
-
-        Arguments:
-            layer: The layer to set the value on, an element name of the
-                   ValueLayers dict.
-            key: The key of the element to set.
-            value: The value to set.
-        """
         if key in self.layers[layer]:
             self.layers[layer][key].setv(layer, value)
         else:
@@ -181,10 +192,17 @@ class ValueList(Section):
             self.layers[layer][key] = val
 
     def from_cp(self, sect):
-        """Initialize the values from a configparser section."""
         keytype = self.keytype()
         valtype = self.valtype()
         for k, v in sect.items():
             keytype.validate(k)
             valtype.validate(v)
             self.setv('conf', k, v)
+
+    def dump_userconfig(self):
+        changed = []
+        mapping = ChainMap(self.layers['temp'], self.layers['conf'])
+        for k, v in mapping.items():
+            if v.value != self.layers['default'][k].value:
+                changed.append((k, v.value))
+        return changed