[git_common] Fix memoize_one type check

pyright doesn't like assigning random functions to function
attributes, as you might imagine.

The new implementation is much cleaner if I say so myself.

The memoize tests also pass FWIW.

Change-Id: Ie37b14f48004b81270c08b4d073c323b8b4ebd54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5762788
Commit-Queue: Allen Li <ayatane@chromium.org>
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>

git_common.py

@@ -41,7 +41,10 @@ import tempfile
 import textwrap
 import time
 import typing
+from typing import Any
 from typing import AnyStr
+from typing import Callable
+from typing import ContextManager
 from typing import Optional
 from typing import Tuple
 
@@ -154,6 +157,40 @@ class BadCommitRefException(Exception):
         super(BadCommitRefException, self).__init__(msg)
 
 
+class _MemoizeWrapper(object):
+
+    def __init__(self, f: Callable[[Any], Any], *, threadsafe: bool):
+        self._f: Callable[[Any], Any] = f
+        self._cache: dict[Any, Any] = {}
+        self._lock: ContextManager = contextlib.nullcontext()
+        if threadsafe:
+            self._lock = threading.Lock()
+
+    def __call__(self, arg: Any) -> Any:
+        ret = self.get(arg)
+        if ret is None:
+            ret = self._f(arg)
+            if ret is not None:
+                self.set(arg, ret)
+        return ret
+
+    def get(self, key: Any, default: Any = None) -> Any:
+        with self._lock:
+            return self._cache.get(key, default)
+
+    def set(self, key: Any, value: Any) -> None:
+        with self._lock:
+            self._cache[key] = value
+
+    def clear(self) -> None:
+        with self._lock:
+            self._cache.clear()
+
+    def update(self, other: dict[Any, Any]) -> None:
+        with self._lock:
+            self._cache.update(other)
+
+
 def memoize_one(*, threadsafe: bool):
     """Memoizes a single-argument pure function.
 
@@ -172,19 +209,6 @@ def memoize_one(*, threadsafe: bool):
             unittests.
         * update(other) - Updates the contents of the cache from another dict.
     """
-    if threadsafe:
-
-        def withlock(lock, f):
-            def inner(*args, **kwargs):
-                with lock:
-                    return f(*args, **kwargs)
-
-            return inner
-    else:
-
-        def withlock(_lock, f):
-            return f
-
     def decorator(f):
         # Instantiate the lock in decorator, in case users of memoize_one do:
         #
@@ -195,26 +219,8 @@ def memoize_one(*, threadsafe: bool):
         #
         # @memoizer
         # def fn2(val): ...
-
-        lock = threading.Lock() if threadsafe else None
-        cache = {}
-        _get = withlock(lock, cache.get)
-        _set = withlock(lock, cache.__setitem__)
-
-        @functools.wraps(f)
-        def inner(arg):
-            ret = _get(arg)
-            if ret is None:
-                ret = f(arg)
-                if ret is not None:
-                    _set(arg, ret)
-            return ret
-
-        inner.get = _get
-        inner.set = _set
-        inner.clear = withlock(lock, cache.clear)
-        inner.update = withlock(lock, cache.update)
-        return inner
+        wrapped = _MemoizeWrapper(f, threadsafe=threadsafe)
+        return functools.wraps(f)(wrapped)
 
     return decorator