Fix AttributeError: __metadata__ on Python 3.13

[kamyarghajar]

Description

This PR fixes a breaking AttributeError: __metadata__ encountered when running injector on Python 3.13.

In Python 3.13, certain type hints (particularly those involving Literal, Union, or classes using slots=True) can be identified as a specialization of Annotated but do not consistently expose the __metadata__ attribute. Direct access to v.__metadata__ now raises an AttributeError in these scenarios, whereas in previous Python versions it would typically return an empty tuple or simply not be triggered in this specific code path.

Changes

Modified the has_injectable_parameters check in injector/__init__.py to use getattr() when accessing __metadata__.

# Before
_inject_marker in v.__metadata__

# After
_inject_marker in getattr(v, "__metadata__", ())

This ensures that if the attribute is missing, the code defaults to an empty tuple, allowing the in check to fail gracefully instead of raising an exception.

[davidparsson]

Thanks for your contribution! Would you be able to include a test that exposes the problem? The test suite passed on 3.13 before this change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.54%. Comparing base (c58c7a2) to head (515a1f2).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #304   +/-   ##
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  Coverage   96.54%   96.54%           
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  Files           1        1           
  Lines         608      608           
  Branches      103      103           
=======================================
  Hits          587      587           
  Misses         15       15           
  Partials        6        6           

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[davidparsson]

Oh, I saw your issue just now. I can add a test myself based on that. Thanks again!

[davidparsson]

Fixes #303

[davidparsson]

This is released in 0.24.0