Passing wrong number of arguments to generic produces runtime errors
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Description
In pypa/hatch#2437, we see a change to a generic type, adding an extra parameter, causing a run-time failure, and since this was used in a build plugin, it cause a build failure and my package to fail to install.
pdm.exceptions.BuildError: Build backend raised error: Showing the last 10 lines of the build output:
class GitInfoBuildHook(BuildHookInterface[Any]):
~~~~~~~~~~~~~~~~~~^^^^^
File "/usr/lib/python3.12/typing.py", line 398, in inner
return func(*args, **kwds)
^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/typing.py", line 1083, in _generic_class_getitem
_check_generic(cls, params, len(cls.__parameters__))
File "/tmp/pdm-build-env-4xoutxun-shared/lib/python3.12/site-packages/typing_extensions.py", line 3274, in _check_generic
raise TypeError(f"Too {'many' if alen > elen else 'few'} arguments"
TypeError: Too few arguments for <class 'hatchling.builders.hooks.plugin.interface.BuildHookInterface'>; actual 1, expected at least 2
I find this behavior fairly surprising; I would only expect type errors in an annotation to cause errors when doing typechecking, not runtime errors like this.
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Research direction
Start by reproducing the reported generic-parameter failure through the typing.py path shown in the traceback, then compare the corresponding validation in typing_extensions.py. The issue is resolved when the intended behavior for incorrect generic argument counts is established and covered by a regression test without breaking valid runtime typing use.
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Assessment
- Tech stack
- python
- Domain
- backend
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100