tests: add a proper test checking for from __future__ import annotati…

…ons handling

README.md

@@ -140,18 +140,18 @@ and compares it against the previously stored hash value.
 
 
 
-* automatic schema inference: [1](src/cachew/tests/test_cachew.py#L388), [2](src/cachew/tests/test_cachew.py#L402)
+* automatic schema inference: [1](src/cachew/tests/test_cachew.py#L390), [2](src/cachew/tests/test_cachew.py#L404)
 * supported types:    
 
     * primitive: `str`, `int`, `float`, `bool`, `datetime`, `date`, `Exception`
 
-      See [tests.test_types](src/cachew/tests/test_cachew.py#L714), [tests.test_primitive](src/cachew/tests/test_cachew.py#L748), [tests.test_dates](src/cachew/tests/test_cachew.py#L668), [tests.test_exceptions](src/cachew/tests/test_cachew.py#L1144)
-    * [@dataclass and NamedTuple](src/cachew/tests/test_cachew.py#L630)
-    * [Optional](src/cachew/tests/test_cachew.py#L532) types
-    * [Union](src/cachew/tests/test_cachew.py#L854) types
-    * [nested datatypes](src/cachew/tests/test_cachew.py#L448)
+      See [tests.test_types](src/cachew/tests/test_cachew.py#L713), [tests.test_primitive](src/cachew/tests/test_cachew.py#L747), [tests.test_dates](src/cachew/tests/test_cachew.py#L667), [tests.test_exceptions](src/cachew/tests/test_cachew.py#L1145)
+    * [@dataclass and NamedTuple](src/cachew/tests/test_cachew.py#L632)
+    * [Optional](src/cachew/tests/test_cachew.py#L534) types
+    * [Union](src/cachew/tests/test_cachew.py#L853) types
+    * [nested datatypes](src/cachew/tests/test_cachew.py#L450)
 
-* detects [datatype schema changes](src/cachew/tests/test_cachew.py#L478) and discards old data automatically
+* detects [datatype schema changes](src/cachew/tests/test_cachew.py#L480) and discards old data automatically
 
 
 # Performance
@@ -170,15 +170,15 @@ You can also use [extensive unit tests](src/cachew/tests/test_cachew.py) as a re
 
 Some useful (but optional) arguments of `@cachew` decorator:
 
-* `cache_path` can be a directory, or a callable that [returns a path](src/cachew/tests/test_cachew.py#L425) and depends on function's arguments.
+* `cache_path` can be a directory, or a callable that [returns a path](src/cachew/tests/test_cachew.py#L427) and depends on function's arguments.
 
    By default, `settings.DEFAULT_CACHEW_DIR` is used.
 
 * `depends_on` is a function which determines whether your inputs have changed, and the cache needs to be invalidated.
 
    By default it just uses string representation of the arguments, you can also specify a custom callable.
 
-   For instance, it can be used to [discard cache](src/cachew/tests/test_cachew.py#L120) if the input file was modified.
+   For instance, it can be used to [discard cache](src/cachew/tests/test_cachew.py#L122) if the input file was modified.
 
 * `cls` is the type that would be serialized.
 

src/cachew/tests/test_cachew.py

@@ -1,7 +1,9 @@
 import hashlib
 import inspect
+import os
 import string
 import sys
+import textwrap
 import time
 import timeit
 from concurrent.futures import ProcessPoolExecutor
@@ -638,10 +640,7 @@ def get_dataclasses() -> Iterator[Test]:
 
 def test_inner_class(tmp_path: Path) -> None:
     # NOTE: this doesn't work at the moment if from __future__ import annotations is used in client code (e.g. on top of this test)
-    # because then annotations end up as strings and we can't eval it as we don't have access to a class defined inside function
-    # keeping this test just to keep track of whether this is fixed at some point
-    # possibly relevant:
-    # - https://peps.python.org/pep-0563/#keeping-the-ability-to-use-function-local-state-when-defining-annotations
+    # see test_future_annotations for more info
 
     @dataclass
     class InnerDataclass:
@@ -1014,13 +1013,14 @@ def orig2():
 
 
 @pytest.mark.parametrize('throw', [False, True])
-def test_future_annotations(*, tmp_path: Path, throw: bool) -> None:
+def test_bad_annotation(*, 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'''
+    src.write_text(
+        f'''
 from __future__ import annotations
 
 from cachew import settings, cachew
@@ -1032,7 +1032,8 @@ def fun() -> BadType:
     return 0
 
 fun()
-'''.lstrip())
+'''.lstrip()
+    )
 
     ctx = pytest.raises(Exception) if throw else nullcontext()
     with ctx:
@@ -1453,3 +1454,94 @@ def fun_multiple() -> Iterable[int]:
 
     assert (tmp_path / callable_name(fun_single)).exists()
     assert (tmp_path / callable_name(fun_multiple)).exists()
+
+
+@pytest.mark.parametrize('use_future_annotations', [False, True])
+@pytest.mark.parametrize('local', [False, True])
+@pytest.mark.parametrize('throw', [False, True])
+def test_future_annotations(
+    *,
+    use_future_annotations: bool,
+    local: bool,
+    throw: bool,
+    tmp_path: Path,
+) -> None:
+    """
+    Checks handling of postponed evaluation of annotations (from __future__ import annotations)
+    """
+
+    if sys.version_info[:2] <= (3, 8):
+        pytest.skip("too annoying to adjust for 3.8 and it's EOL soon anyway")
+
+    # NOTE: to avoid weird interactions with existing interpreter in which pytest is running
+    #  , we compose a program and running in python directly instead
+    #  (also not sure if it's even possible to tweak postponed annotations without doing that)
+
+    if use_future_annotations and local and throw:
+        # when annotation is local (like inner class), then they end up as strings
+        #  so we can't eval it as we don't have access to a class defined inside function
+        #  keeping this test just to keep track of whether this is fixed at some point
+        #  possibly relevant:
+        #  - https://peps.python.org/pep-0563/#keeping-the-ability-to-use-function-local-state-when-defining-annotations
+        pytest.skip("local aliases/classses don't work with from __future__ import annotations")
+
+    _PREAMBLE = f'''
+from pathlib import Path
+import tempfile
+
+from cachew import cachew, settings
+settings.THROW_ON_ERROR = {throw}
+
+temp_dir = tempfile.TemporaryDirectory()
+td = Path(temp_dir.name)
+
+'''
+
+    _TEST = '''
+T = int
+
+@cachew(td)
+def fun() -> list[T]:
+    print("called")
+    return [1, 2]
+
+assert list(fun()) == [1, 2]
+assert list(fun()) == [1, 2]
+'''
+
+    if use_future_annotations:
+        code = '''
+from __future__ import annotations
+'''
+    else:
+        code = ''
+
+    code += _PREAMBLE
+
+    if local:
+        code += f'''
+def test() -> None:
+{textwrap.indent(_TEST, prefix=" ")}
+
+test()
+'''
+    else:
+        code += _TEST
+
+    run_py = tmp_path / 'run.py'
+    run_py.write_text(code)
+
+    cache_dir = tmp_path / 'cache'
+    cache_dir.mkdir()
+
+    res = check_output(
+        [sys.executable, run_py],
+        env={'TMPDIR': str(cache_dir), **os.environ},
+        text=True,
+    )
+    called = int(res.count('called'))
+    if use_future_annotations and local and not throw:
+        # cachew fails to set up, so no caching but at least it works otherwise
+        assert called == 2
+    else:
+        assert called == 1