Fix config validation for String types.

Fixes #1231.

qutebrowser/config/configtypes.py

@@ -258,6 +258,13 @@ class String(BaseType):
         self._basic_validation(value)
         if not value:
             return
+
+        if self.valid_values is not None:
+            if value not in self.valid_values:
+                raise configexc.ValidationError(
+                    value, "valid values: {}".format(', '.join(
+                        self.valid_values)))
+
         if self.forbidden is not None and any(c in value
                                               for c in self.forbidden):
             raise configexc.ValidationError(value, "may not contain the chars "

tests/unit/config/test_configtypes.py

@@ -305,6 +305,8 @@ class TestString:
         ({'minlen': 2}, 'fo'),
         ({'minlen': 2, 'maxlen': 3}, 'fo'),
         ({'minlen': 2, 'maxlen': 3}, 'foo'),
+        # valid_values
+        ({'valid_values': configtypes.ValidValues('fooo')}, 'fooo'),
     ])
     def test_validate_valid(self, klass, kwargs, val):
         klass(**kwargs).validate(val)
@@ -319,6 +321,8 @@ class TestString:
         ({'maxlen': 2}, 'fob'),
         ({'minlen': 2, 'maxlen': 3}, 'f'),
         ({'minlen': 2, 'maxlen': 3}, 'fooo'),
+        # valid_values
+        ({'valid_values': configtypes.ValidValues('blah')}, 'fooo'),
     ])
     def test_validate_invalid(self, klass, kwargs, val):
         with pytest.raises(configexc.ValidationError):