fix: type CachedResponse.__init__ for mypy --strict (#628)

CHANGES.rst

@@ -4,6 +4,8 @@ Changelog
 Unreleased
 ----------
 
+- Type ``CachedResponse.__init__`` so it doesn't trigger mypy ``[no-untyped-call]``
+  in strict downstream codebases. :issue:`628`
 - Docs: clarify that ``@memoize`` uses ``repr(obj)``
   (or ``__caching_id__``) for the ``self``/``cls`` identity, not Python's
   :func:`id`. :issue:`555`

src/flask_caching/__init__.py

@@ -57,9 +57,13 @@ class CachedResponse(Response):
     to override the cache TTL dynamically
     """
 
-    timeout = None
+    timeout: int | None = None
 
-    def __init__(self, response, timeout):
+    def __init__(self, response: Response, timeout: int | None) -> None:
+        # ``CachedResponse`` adopts the state of an existing Response in
+        # place rather than calling ``Response.__init__``; copying
+        # ``__dict__`` preserves headers, status and body without having
+        # to round-trip the response through Werkzeug's constructor.
         self.__dict__ = response.__dict__
         self.timeout = timeout
 

tests/test_init.py

@@ -1,9 +1,12 @@
 import importlib.util
+import inspect
 
 import pytest
 from flask import Flask
+from flask import make_response
 
 from flask_caching import Cache
+from flask_caching import CachedResponse
 from flask_caching.backends import FileSystemCache
 from flask_caching.backends import MemcachedCache
 from flask_caching.backends import NullCache
@@ -61,3 +64,37 @@ def test_init_nullcache(cache_type, app, tmp_path):
     cache = Cache(app=app)
 
     assert isinstance(app.extensions["cache"][cache], cache_type)
+
+
+def test_cached_response_init_is_typed():
+    """Regression test for issue #628.
+
+    ``CachedResponse.__init__`` must declare a return type and parameter
+    types so that mypy ``--strict`` doesn't flag construction in typed
+    code with ``[no-untyped-call]``. See
+    https://github.com/pallets-eco/flask-caching/issues/628.
+    """
+    sig = inspect.signature(CachedResponse.__init__)
+    # __init__ should declare ``-> None`` rather than be untyped.
+    # inspect.signature returns the literal ``None`` for ``-> None``.
+    assert sig.return_annotation is None, (
+        f"CachedResponse.__init__ return annotation is {sig.return_annotation!r}; "
+        "expected None"
+    )
+    # All non-self parameters should carry an annotation.
+    for name, param in sig.parameters.items():
+        if name == "self":
+            continue
+        assert (
+            param.annotation is not inspect.Parameter.empty
+        ), f"CachedResponse.__init__ parameter {name!r} has no annotation"
+
+
+def test_cached_response_construction_with_flask_response():
+    """Sanity check that CachedResponse still wraps a flask Response."""
+    app = Flask(__name__)
+    with app.test_request_context():
+        resp = make_response("hi")
+        cached = CachedResponse(resp, 10)
+    assert cached.timeout == 10
+    assert cached.get_data(as_text=True) == "hi"