fix handling of undefined type annotations when from __future__ import annotations is on

Author: karlicoss

README.md

@@ -128,7 +128,7 @@ Cachew gives the best of two worlds and makes it both **easy and efficient**. Th
 - first your objects get [converted](src/cachew/marshall/cachew.py#L34) into a simpler JSON-like representation 
 - after that, they are mapped into byte blobs via [`orjson`](https://github.com/ijl/orjson).
 
-When the function is called, cachew [computes the hash of your function's arguments ](src/cachew/__init__.py:#L511)
+When the function is called, cachew [computes the hash of your function's arguments ](src/cachew/__init__.py:#L589)
 and compares it against the previously stored hash value.
 
 - If they match, it would deserialize and yield whatever is stored in the cache database
@@ -145,7 +145,7 @@ and compares it against the previously stored hash value.
 
     * primitive: `str`, `int`, `float`, `bool`, `datetime`, `date`, `Exception`
 
-      See [tests.test_types](src/cachew/tests/test_cachew.py#L697), [tests.test_primitive](src/cachew/tests/test_cachew.py#L731), [tests.test_dates](src/cachew/tests/test_cachew.py#L651), [tests.test_exceptions](src/cachew/tests/test_cachew.py#L1101)
+      See [tests.test_types](src/cachew/tests/test_cachew.py#L697), [tests.test_primitive](src/cachew/tests/test_cachew.py#L731), [tests.test_dates](src/cachew/tests/test_cachew.py#L651), [tests.test_exceptions](src/cachew/tests/test_cachew.py#L1127)
     * [@dataclass and NamedTuple](src/cachew/tests/test_cachew.py#L613)
     * [Optional](src/cachew/tests/test_cachew.py#L515) types
     * [Union](src/cachew/tests/test_cachew.py#L837) types
@@ -165,7 +165,7 @@ You can find some of my performance tests in [benchmarks/](benchmarks) dir, and
 
 
 # Using
-See [docstring](src/cachew/__init__.py#L290) for up-to-date documentation on parameters and return types. 
+See [docstring](src/cachew/__init__.py#L296) for up-to-date documentation on parameters and return types. 
 You can also use [extensive unit tests](src/cachew/tests/test_cachew.py) as a reference.
 
 Some useful (but optional) arguments of `@cachew` decorator:
@@ -271,7 +271,7 @@ Now you can use `@mcachew` in place of `@cachew`, and be certain things don't br
 ## Settings
 
 
-[cachew.settings](src/cachew/__init__.py#L66) exposes some parameters that allow you to control `cachew` behaviour:
+[cachew.settings](src/cachew/__init__.py#L67) exposes some parameters that allow you to control `cachew` behaviour:
 - `ENABLE`: set to `False` if you want to disable caching for without removing the decorators (useful for testing and debugging).
    You can also use [cachew.extra.disabled_cachew](src/cachew/extra.py#L21) context manager to do it temporarily.
 - `DEFAULT_CACHEW_DIR`: override to set a different base directory. The default is the "user cache directory" (see [appdirs docs](https://github.com/ActiveState/appdirs#some-example-output)).

src/cachew/__init__.py

@@ -213,7 +213,12 @@ def infer_return_type(func) -> Union[Failure, Inferred]:
     >>> infer_return_type(unsupported_list)
     "can't infer type from typing.List[cachew.Custom]: can't cache <class 'cachew.Custom'>"
     """
-    hints = get_type_hints(func)
+    try:
+        hints = get_type_hints(func)
+    except Exception as ne:
+        # get_type_hints might fail if types are forward defined or missing
+        # see test_future_annotation for an example
+        return str(ne)
     rtype = hints.get('return', None)
     if rtype is None:
         return f"no return type annotation on {func}"

src/cachew/logging_helper.py

@@ -214,7 +214,7 @@ def get_enlighten():
         return Mock()
 
     try:
-        import enlighten  # type: ignore[import]
+        import enlighten  # type: ignore[import-untyped]
     except ModuleNotFoundError:
         warnings.warn("You might want to 'pip install enlighten' for a nice progress bar")
 

src/cachew/tests/test_cachew.py

@@ -996,6 +996,32 @@ def orig2():
             assert list(fun()) == [123]
 
 
+@pytest.mark.parametrize('throw', [False, True])
+def test_future_annotations(tmp_path: Path, throw: bool) -> None:
+    """
+    this will work in runtime without cachew if from __future__ import annotations is used
+    so should work with cachew decorator as well
+    """
+    src = tmp_path / 'src.py'
+    src.write_text(f'''
+from __future__ import annotations
+
+from cachew import settings, cachew
+settings.THROW_ON_ERROR = {throw}
+
+@cachew
+def fun() -> BadType:
+    print("called!")
+    return 0
+
+fun()
+'''.lstrip())
+
+    ctx = pytest.raises(Exception) if throw else nullcontext()
+    with ctx:
+        assert check_output([sys.executable, src], text=True).strip() == "called!"
+
+
 def test_recursive_simple(tmp_path: Path) -> None:
     d0 = 0
     d1 = 1000