Fix choices validation with unannotated args

Something like:

    @cmdutils.argument('foo', choices=['one', 'two'])
    def func(foo):
        # ...

didn't actually validate the foo argument, since the inferred type of
the argument is None, and that skipped all conversion (and thus
validation).

Fixes #1871
See #1885

qutebrowser/commands/argparser.py

@@ -119,7 +119,7 @@ def type_conv(param, typ, value, *, str_choices=None):
     if utils.is_enum(typ):
         _check_choices(param, value, [arg_name(e.name) for e in typ])
         return typ[value.replace('-', '_')]
-    elif typ is str:
+    elif typ in [str, None]:
         if str_choices is not None:
             _check_choices(param, value, str_choices)
         return value

qutebrowser/commands/command.py

@@ -422,11 +422,9 @@ class Command:
             choices = self.get_arg_info(param).choices
             value = argparser.multitype_conv(param, types, value,
                                              str_choices=choices)
-        elif typ is str:
+        elif typ in [str, None]:
             choices = self.get_arg_info(param).choices
             value = argparser.type_conv(param, typ, value, str_choices=choices)
-        elif typ is None:
-            pass
         elif typ is bool:  # no type conversion for flags
             assert isinstance(value, bool)
         else:

tests/unit/commands/test_cmdutils.py

@@ -295,6 +295,20 @@ class TestRegister:
         else:
             assert cmd._get_call_args(win_id=0) == ([expected], {})
 
+    def test_choices_no_annotation(self):
+        # https://github.com/The-Compiler/qutebrowser/issues/1871
+        @cmdutils.register()
+        @cmdutils.argument('arg', choices=['foo', 'bar'])
+        def fun(arg):
+            """Blah."""
+            pass
+
+        cmd = cmdutils.cmd_dict['fun']
+        cmd.namespace = cmd.parser.parse_args(['fish'])
+
+        with pytest.raises(cmdexc.ArgumentTypeError):
+            cmd._get_call_args(win_id=0)
+
     def test_pos_arg_info(self):
         @cmdutils.register()
         @cmdutils.argument('foo', choices=('a', 'b'))