decorator: Strengthen types of signature-preserving decorators.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/decorator.py

@@ -4,7 +4,7 @@ import logging
 import urllib
 from functools import wraps
 from io import BytesIO
-from typing import Any, Callable, Dict, Optional, Tuple, TypeVar, Union
+from typing import Any, Callable, Dict, Optional, Tuple, TypeVar, Union, cast
 
 import django_otp
 import ujson
@@ -61,8 +61,6 @@ else:  # nocoverage # Hack here basically to make impossible code paths compile
     get_remote_server_by_uuid = Mock()
     RemoteZulipServer = Mock()  # type: ignore[misc] # https://github.com/JukkaL/mypy/issues/1188
 
-ReturnT = TypeVar('ReturnT')
-
 webhook_logger = logging.getLogger("zulip.zerver.webhooks")
 log_to_file(webhook_logger, settings.API_KEY_ONLY_WEBHOOK_LOG_PATH)
 
@@ -70,17 +68,19 @@ webhook_unexpected_events_logger = logging.getLogger("zulip.zerver.lib.webhooks.
 log_to_file(webhook_unexpected_events_logger,
             settings.WEBHOOK_UNEXPECTED_EVENTS_LOG_PATH)
 
-def cachify(method: Callable[..., ReturnT]) -> Callable[..., ReturnT]:
+FuncT = TypeVar('FuncT', bound=Callable[..., object])
-    dct: Dict[Tuple[Any, ...], ReturnT] = {}
 
-    def cache_wrapper(*args: Any) -> ReturnT:
+def cachify(method: FuncT) -> FuncT:
+    dct: Dict[Tuple[object, ...], object] = {}
+
+    def cache_wrapper(*args: object) -> object:
         tup = tuple(args)
         if tup in dct:
             return dct[tup]
         result = method(*args)
         dct[tup] = result
         return result
-    return cache_wrapper
+    return cast(FuncT, cache_wrapper)  # https://github.com/python/mypy/issues/1927
 
 def update_user_activity(request: HttpRequest, user_profile: UserProfile,
                          query: Optional[str]) -> None:
@@ -732,19 +732,18 @@ def internal_notify_view(is_tornado_view: bool) -> Callable[[ViewFuncT], ViewFun
 def to_utc_datetime(timestamp: str) -> datetime.datetime:
     return timestamp_to_datetime(float(timestamp))
 
-def statsd_increment(counter: str, val: int=1,
+def statsd_increment(counter: str, val: int=1) -> Callable[[FuncT], FuncT]:
-                     ) -> Callable[[Callable[..., ReturnT]], Callable[..., ReturnT]]:
     """Increments a statsd counter on completion of the
     decorated function.
 
     Pass the name of the counter to this decorator-returning function."""
-    def wrapper(func: Callable[..., ReturnT]) -> Callable[..., ReturnT]:
+    def wrapper(func: FuncT) -> FuncT:
         @wraps(func)
-        def wrapped_func(*args: Any, **kwargs: Any) -> ReturnT:
+        def wrapped_func(*args: object, **kwargs: object) -> object:
             ret = func(*args, **kwargs)
             statsd.incr(counter, val)
             return ret
-        return wrapped_func
+        return cast(FuncT, wrapped_func)  # https://github.com/python/mypy/issues/1927
     return wrapper
 
 def rate_limit_user(request: HttpRequest, user: UserProfile, domain: str) -> None:

zerver/lib/cache.py

@@ -20,6 +20,7 @@ from typing import (
     Sequence,
     Tuple,
     TypeVar,
+    cast,
 )
 
 from django.conf import settings
@@ -39,7 +40,7 @@ if TYPE_CHECKING:
 
 MEMCACHED_MAX_KEY_LENGTH = 250
 
-ReturnT = TypeVar('ReturnT')  # Useful for matching return types via Callable[..., ReturnT]
+FuncT = TypeVar('FuncT', bound=Callable[..., object])
 
 logger = logging.getLogger()
 
@@ -127,15 +128,15 @@ def get_cache_backend(cache_name: Optional[str]) -> BaseCache:
 def get_cache_with_key(
         keyfunc: Callable[..., str],
         cache_name: Optional[str]=None,
-) -> Callable[[Callable[..., ReturnT]], Callable[..., ReturnT]]:
+) -> Callable[[FuncT], FuncT]:
     """
     The main goal of this function getting value from the cache like in the "cache_with_key".
     A cache value can contain any data including the "None", so
     here used exception for case if value isn't found in the cache.
     """
-    def decorator(func: Callable[..., ReturnT]) -> (Callable[..., ReturnT]):
+    def decorator(func: FuncT) -> FuncT:
         @wraps(func)
-        def func_with_caching(*args: Any, **kwargs: Any) -> Callable[..., ReturnT]:
+        def func_with_caching(*args: object, **kwargs: object) -> object:
             key = keyfunc(*args, **kwargs)
             try:
                 val = cache_get(key, cache_name=cache_name)
@@ -148,14 +149,14 @@ def get_cache_with_key(
                 return val[0]
             raise NotFoundInCache()
 
-        return func_with_caching
+        return cast(FuncT, func_with_caching)  # https://github.com/python/mypy/issues/1927
 
     return decorator
 
 def cache_with_key(
         keyfunc: Callable[..., str], cache_name: Optional[str]=None,
         timeout: Optional[int]=None, with_statsd_key: Optional[str]=None,
-) -> Callable[[Callable[..., ReturnT]], Callable[..., ReturnT]]:
+) -> Callable[[FuncT], FuncT]:
     """Decorator which applies Django caching to a function.
 
        Decorator argument is a function which computes a cache key
@@ -163,9 +164,9 @@ def cache_with_key(
        for avoiding collisions with other uses of this decorator or
        other uses of caching."""
 
-    def decorator(func: Callable[..., ReturnT]) -> Callable[..., ReturnT]:
+    def decorator(func: FuncT) -> FuncT:
         @wraps(func)
-        def func_with_caching(*args: Any, **kwargs: Any) -> ReturnT:
+        def func_with_caching(*args: object, **kwargs: object) -> object:
             key = keyfunc(*args, **kwargs)
 
             try:
@@ -198,7 +199,7 @@ def cache_with_key(
 
             return val
 
-        return func_with_caching
+        return cast(FuncT, func_with_caching)  # https://github.com/python/mypy/issues/1927
 
     return decorator
 

zerver/lib/profile.py

@@ -1,10 +1,10 @@
 import cProfile
 from functools import wraps
-from typing import Any, Callable, TypeVar
+from typing import Callable, TypeVar, cast
 
-ReturnT = TypeVar('ReturnT')
+FuncT = TypeVar('FuncT', bound=Callable[..., object])
 
-def profiled(func: Callable[..., ReturnT]) -> Callable[..., ReturnT]:
+def profiled(func: FuncT) -> FuncT:
     """
     This decorator should obviously be used only in a dev environment.
     It works best when surrounding a function that you expect to be
@@ -21,11 +21,13 @@ def profiled(func: Callable[..., ReturnT]) -> Callable[..., ReturnT]:
         ./tools/show-profile-results test_ratelimit_decrease.profile
 
     """
+    func_: Callable[..., object] = func  # work around https://github.com/python/mypy/issues/9075
+
     @wraps(func)
-    def wrapped_func(*args: Any, **kwargs: Any) -> ReturnT:
+    def wrapped_func(*args: object, **kwargs: object) -> object:
         fn = func.__name__ + ".profile"
         prof = cProfile.Profile()
-        retval: ReturnT = prof.runcall(func, *args, **kwargs)
+        retval = prof.runcall(func_, *args, **kwargs)
         prof.dump_stats(fn)
         return retval
-    return wrapped_func
+    return cast(FuncT, wrapped_func)  # https://github.com/python/mypy/issues/1927

zerver/openapi/python_examples.py

@@ -2,7 +2,7 @@ import json
 import os
 import sys
 from functools import wraps
-from typing import Any, Callable, Dict, Iterable, List, Optional, Set
+from typing import Any, Callable, Dict, Iterable, List, Optional, Set, TypeVar, cast
 
 from zulip import Client
 
@@ -12,27 +12,29 @@ from zerver.openapi.openapi import validate_against_openapi_schema
 
 ZULIP_DIR = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
-TEST_FUNCTIONS: Dict[str, Callable[..., None]] = dict()
+TEST_FUNCTIONS: Dict[str, Callable[..., object]] = dict()
 REGISTERED_TEST_FUNCTIONS: Set[str] = set()
 CALLED_TEST_FUNCTIONS: Set[str] = set()
 
-def openapi_test_function(endpoint: str) -> Callable[[Callable[..., Any]], Callable[..., Any]]:
+FuncT = TypeVar("FuncT", bound=Callable[..., object])
+
+def openapi_test_function(endpoint: str) -> Callable[[FuncT], FuncT]:
     """This decorator is used to register an openapi test function with
     its endpoint. Example usage:
 
     @openapi_test_function("/messages/render:post")
     def ...
     """
-    def wrapper(test_func: Callable[..., Any]) -> Callable[..., Any]:
+    def wrapper(test_func: FuncT) -> FuncT:
         @wraps(test_func)
-        def _record_calls_wrapper(*args: Any, **kwargs: Any) -> Any:
+        def _record_calls_wrapper(*args: object, **kwargs: object) -> object:
             CALLED_TEST_FUNCTIONS.add(test_func.__name__)
             return test_func(*args, **kwargs)
 
         REGISTERED_TEST_FUNCTIONS.add(test_func.__name__)
         TEST_FUNCTIONS[endpoint] = _record_calls_wrapper
 
-        return _record_calls_wrapper
+        return cast(FuncT, _record_calls_wrapper)  # https://github.com/python/mypy/issues/1927
     return wrapper
 
 def ensure_users(ids_list: List[int], user_names: List[str]) -> None: