Reject hints -> chars containing duplicate chars

Fixes #1286.

CHANGELOG.asciidoc

@@ -48,6 +48,7 @@ Fixed
 - Fixed crash when downloading a file without any path information (e.g a
   magnet link).
 - Fixed crashes when opening an empty URL (e.g. via pasting).
+- Fixed validation of duplicate values in `hints -> chars`.
 
 v0.5.1
 ------

qutebrowser/config/configdata.py

@@ -870,7 +870,7 @@ def data(readonly=False):
              "Mode to use for hints."),
 
             ('chars',
-             SettingValue(typ.String(minlen=2, completions=[
+             SettingValue(typ.UniqueCharString(minlen=2, completions=[
                  ('asdfghjkl', "Home row"),
                  ('dhtnaoeu', "Home row (Dvorak)"),
                  ('abcdefghijklmnopqrstuvwxyz', "All letters"),

qutebrowser/config/configtypes.py

@@ -283,6 +283,21 @@ class String(BaseType):
             return super().complete()
 
 
+class UniqueCharString(String):
+
+    """A string which may not contain duplicate chars."""
+
+    def validate(self, value):
+        super().validate(value)
+        if not value:
+            return
+
+        # Check for duplicate values
+        if len(set(value)) != len(value):
+            raise configexc.ValidationError(
+                value, "String contains duplicate values!")
+
+
 class List(BaseType):
 
     """Base class for a (string-)list setting."""

tests/unit/config/test_configtypes.py

@@ -278,9 +278,9 @@ class TestString:
 
     """Test String."""
 
-    @pytest.fixture
-    def klass(self):
-        return configtypes.String
+    @pytest.fixture(params=[configtypes.String, configtypes.UniqueCharString])
+    def klass(self, request):
+        return request.param
 
     @pytest.mark.parametrize('minlen, maxlen', [(1, None), (None, 1)])
     def test_lengths_valid(self, klass, minlen, maxlen):
@@ -297,16 +297,16 @@ class TestString:
 
     @pytest.mark.parametrize('kwargs, val', [
         ({'none_ok': True}, ''),  # Empty with none_ok
-        ({}, "Hello World! :-)"),
+        ({}, "Test! :-)"),
         # Forbidden chars
-        ({'forbidden': 'xyz'}, 'foobar'),
+        ({'forbidden': 'xyz'}, 'fobar'),
         ({'forbidden': 'xyz'}, 'foXbar'),
         # Lengths
         ({'minlen': 2}, 'fo'),
         ({'minlen': 2, 'maxlen': 3}, 'fo'),
-        ({'minlen': 2, 'maxlen': 3}, 'foo'),
+        ({'minlen': 2, 'maxlen': 3}, 'abc'),
         # valid_values
-        ({'valid_values': configtypes.ValidValues('fooo')}, 'fooo'),
+        ({'valid_values': configtypes.ValidValues('abcd')}, 'abcd'),
     ])
     def test_validate_valid(self, klass, kwargs, val):
         klass(**kwargs).validate(val)
@@ -320,16 +320,21 @@ class TestString:
         ({'minlen': 2}, 'f'),
         ({'maxlen': 2}, 'fob'),
         ({'minlen': 2, 'maxlen': 3}, 'f'),
-        ({'minlen': 2, 'maxlen': 3}, 'fooo'),
+        ({'minlen': 2, 'maxlen': 3}, 'abcd'),
         # valid_values
-        ({'valid_values': configtypes.ValidValues('blah')}, 'fooo'),
+        ({'valid_values': configtypes.ValidValues('blah')}, 'abcd'),
     ])
     def test_validate_invalid(self, klass, kwargs, val):
         with pytest.raises(configexc.ValidationError):
             klass(**kwargs).validate(val)
 
+    def test_validate_duplicate_invalid(self):
+        typ = configtypes.UniqueCharString()
+        with pytest.raises(configexc.ValidationError):
+            typ.validate('foobar')
+
     def test_transform(self, klass):
-        assert klass().transform('foobar') == 'foobar'
+        assert klass().transform('fobar') == 'fobar'
 
     @pytest.mark.parametrize('value', [
         None,