Make sure @cmdutils.argument after @register fails

qutebrowser/commands/cmdutils.py

@@ -185,8 +185,10 @@ class argument:  # pylint: disable=invalid-name
         self._kwargs = kwargs
 
     def __call__(self, func):
+        funcname = func.__name__
+
         if self._argname not in inspect.signature(func).parameters:
-            raise ValueError("{} has no argument {}!".format(func.__name__,
+            raise ValueError("{} has no argument {}!".format(funcname,
                                                              self._argname))
 
         # Fill up args which weren't passed
@@ -196,6 +198,10 @@ class argument:  # pylint: disable=invalid-name
 
         if not hasattr(func, 'qute_args'):
             func.qute_args = {}
+        elif func.qute_args is None:
+            raise ValueError("@cmdutils.argument got called above (after) "
+                             "@cmdutils.register for {}!".format(funcname))
+
         func.qute_args[self._argname] = command.ArgInfo(**self._kwargs)
 
         return func

qutebrowser/commands/command.py

@@ -128,6 +128,10 @@ class Command:
 
         args = self._inspect_func()
 
+        # This is checked by future @cmdutils.argument calls so they fail
+        # (as they'd be silently ignored otherwise)
+        self.handler.qute_args = None
+
         if self.completion is not None and len(self.completion) > len(args):
             raise ValueError("Got {} completions, but only {} "
                              "arguments!".format(len(self.completion),

tests/unit/commands/test_cmdutils.py

@@ -260,3 +260,17 @@ class TestArgument:
             'bar': self._arginfo(flag='y')
         }
         assert fun.qute_args == expected
+
+    def test_wrong_order(self):
+        """When @cmdutils.argument is used above (after) @register, fail."""
+        with pytest.raises(ValueError) as excinfo:
+            @cmdutils.argument('bar', flag='y')
+            @cmdutils.register()
+            def fun(bar):
+                """Blah."""
+                pass
+
+        text = ("@cmdutils.argument got called above (after) "
+                "@cmdutils.register for fun!")
+
+        assert str(excinfo.value) == text