Refactor codecs error handlers to use `_PyUnicodeError_GetParams` and extract complex logic into separate functions

[picnixz]

Feature or enhancement

Proposal:

I want to refactor the different codecs handlers in Python/codecs.c to use _PyUnicodeError_GetParams. Some codecs handlers will be refactored as part of #126004 but some others are not subject to issues (namely, the ignore, namereplace, surrogateescape, and surrogatepass handlers do not suffer from crashes, or at least I wasn't able to make them crash easily).

In addition, I also plan to split the handlers into functions instead of 2 or 3 big blocks of code handling a specific exception. For that reason, I will introduce the following helper macros:

#define _PyIsUnicodeEncodeError(EXC)    \
    PyObject_TypeCheck(EXC, (PyTypeObject *)PyExc_UnicodeEncodeError)
#define _PyIsUnicodeDecodeError(EXC)    \
    PyObject_TypeCheck(EXC, (PyTypeObject *)PyExc_UnicodeDecodeError)
#define _PyIsUnicodeTranslateError(EXC) \
    PyObject_TypeCheck(EXC, (PyTypeObject *)PyExc_UnicodeTranslateError)

For handlers that need to be fixed, I will first fix them in-place (no refactorization). Afterwards, I will refactor them and extract the relevant part of the code into functions. That way, the diff will be easier to follow (I've observed that it's much harder to read the diff where I did both so I will revert that part in the existing PRs; EDIT: actually there is no PR doing both fixes and split...).

I'm creating this issue to track the progression of the refactorization if no issue occurs.

cc @vstinner @encukou

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:

No response

Linked PRs

• gh-129173: Use _PyUnicodeError_GetParams in PyCodec_IgnoreErrors #129174
• gh-129173: Use _PyUnicodeError_GetParams in PyCodec_NameReplaceErrors #129135
• gh-129173: Use _PyUnicodeError_GetParams in PyCodec_SurrogatePassErrors #129134
• gh-129173: Use _PyUnicodeError_GetParams in PyCodec_SurrogateEscapeErrors #129175
• gh-129173: refactor PyCodec_ReplaceErrors into separate functions #129893
• gh-129173: simplify PyCodec_XMLCharRefReplaceErrors logic #129894
• gh-129173: refactor PyCodec_BackslashReplaceErrors into separate functions #129895

[picnixz]

The merge plan is as follows:

• complete Incorrect handling of start and end values in codecs error handlers #126004 (fixing only)
• merge gh-129173: Use _PyUnicodeError_GetParams in PyCodec_IgnoreErrors #129174 so that we have the new helpers
• merge the other PRs and use the new helpers (4/4)
• come back to the fixes in Incorrect handling of start and end values in codecs error handlers #126004 and create PRs for this issue in particular (refactorization only)
• merge the cleanup PRs only (3/3)