Refactor `PyUnicodeError` internal C helpers

[picnixz]

Feature or enhancement

Proposal:

Some helpers make the realization of #126004 a bit harder as we end up with many duplicated code. In order to make the related PRs and #127694 smoother, I suggest refactoring the following helpers:

• Unify get_unicode and get_string as a single as_unicode_error_attribute.
• Allow to retrieve the underlying object attribute and its size in one function, say get_unicode_error_object_and_size. This is typically useful for unifying
• The PyUnicode{Encode,Decode,Translate}Error_GetObject public functions can use a common implementation unicode_error_get_object_impl. Since this depends on the underlying object type, the implementation function would take a flag as a parameter to indicate whether it's a bytes or a string.
• All PyUnicode{Encode,Decode}Error_GetEncoding public functions can use a common implementation unicode_error_get_encoding_impl. The encoding is always a string.
• All PyUnicode{Encode,Decode,Translate}Error_{Get,Set}Reason public functions can use a common implementation unicode_error_{get,set}_reason_impl. The reason is always a string.
• All PyUnicode{Encode,Decode,Translate}_{Get,Set}{Start,End} public functions can use a common implementation unicode_error_{get,set}_{start,end}_impl. Since this depends on the underlying object type, the implementation function would take a flag as a parameter to indicate whether it's a bytes or a string.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

#127674 (comment)

Linked PRs

• gh-127787: refactor helpers for PyUnicodeErrorObject internal interface #127789
• gh-127787: Move _PyUnicodeError_GetParams() to the internal C API #128803
• gh-127787: allow to retrieved the clipped slice length in _PyUnicodeError_GetParams #128980

[encukou]

I think the gh-126004 issue can be used for the related refactoring. But I guess this one works as well.

IMO, there can be a _PyUnicodeError_GetParams to get all of object, size, start and end at the same time, and base the public functions on that.
In unicodeobject the compiler could hopefully inline the function and elide the extra work, and codecs usually needs all the values.

[picnixz]

_PyUnicodeError_GetParams

Ah I missed this one. I can add it now (the interface is nice enough). You can comment on the PR which functions you'd like to unify even more.

EDIT: I've added this one and removed un-necessary functions. Now it looks much nicer!

[picnixz]

I can now close this one and move back to fixing the codecs.