mypy: Improve typing for cmdutils/qute_args

See https://github.com/python/mypy/issues/2087

1 files changed, 24 insertions, 7 deletions

diff --git a/qutebrowser/api/cmdutils.py b/qutebrowser/api/cmdutils.py
index 067ebca92..0c367c6bf 100644
--- a/qutebrowser/api/cmdutils.py
+++ b/qutebrowser/api/cmdutils.py
@@ -35,7 +35,7 @@ Possible values:
 
 
 import inspect
-from typing import Any, Callable, Iterable
+from typing import Any, Callable, Iterable, Protocol, Optional, Dict, cast
 
 from qutebrowser.utils import qtutils
 from qutebrowser.commands import command, cmdexc
@@ -90,7 +90,21 @@ def check_exclusive(flags: Iterable[bool], names: Iterable[str]) -> None:
         raise CommandError("Only one of {} can be given!".format(argstr))
 
 
-_CmdHandlerType = Callable[..., Any]
+_CmdHandlerFunc = Callable[..., Any]
+
+
+class _CmdHandlerType(Protocol):
+
+    """A qutebrowser command function, which had qute_args patched on it.
+
+    Applying @cmdutils.argument to a function will patch it with a qute_args attribute.
+    Below, we cast the decorated function to _CmdHandlerType to make mypy aware of this.
+    """
+
+    qute_args: Optional[Dict[str, command.ArgInfo]]
+
+    def __call__(self, *args: Any, **kwargs: Any) -> Any:
+        ...
 
 
 class register:  # noqa: N801,N806 pylint: disable=invalid-name
@@ -118,7 +132,7 @@ class register:  # noqa: N801,N806 pylint: disable=invalid-name
         # The arguments to pass to Command.
         self._kwargs = kwargs
 
-    def __call__(self, func: _CmdHandlerType) -> _CmdHandlerType:
+    def __call__(self, func: _CmdHandlerFunc) -> _CmdHandlerType:
         """Register the command before running the function.
 
         Gets called when a function should be decorated.
@@ -158,7 +172,8 @@ class register:  # noqa: N801,N806 pylint: disable=invalid-name
 
         # This is checked by future @cmdutils.argument calls so they fail
         # (as they'd be silently ignored otherwise)
-        func.qute_args = None  # type: ignore[attr-defined]
+        func = cast(_CmdHandlerType, func)
+        func.qute_args = None
 
         return func
 
@@ -210,19 +225,21 @@ class argument:  # noqa: N801,N806 pylint: disable=invalid-name
         self._argname = argname   # The name of the argument to handle.
         self._kwargs = kwargs  # Valid ArgInfo members.
 
-    def __call__(self, func: _CmdHandlerType) -> _CmdHandlerType:
+    def __call__(self, func: _CmdHandlerFunc) -> _CmdHandlerType:
         funcname = func.__name__
 
         if self._argname not in inspect.signature(func).parameters:
             raise ValueError("{} has no argument {}!".format(funcname,
                                                              self._argname))
+
+        func = cast(_CmdHandlerType, func)
         if not hasattr(func, 'qute_args'):
-            func.qute_args = {}  # type: ignore[attr-defined]
+            func.qute_args = {}
         elif func.qute_args is None:
             raise ValueError("@cmdutils.argument got called above (after) "
                              "@cmdutils.register for {}!".format(funcname))
 
         arginfo = command.ArgInfo(**self._kwargs)
-        func.qute_args[self._argname] = arginfo  # type: ignore[attr-defined]
+        func.qute_args[self._argname] = arginfo
 
         return func