PY_SSIZE_T_MAX is not an integer constant expression

[ov2k]

BPO	46664

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assignee = None
closed_at = None
created_at = <Date 2022-02-06.21:20:42.705>
labels = ['3.7', '3.8', '3.9', '3.10', '3.11', 'expert-C-API', 'type-feature']
title = 'PY_SSIZE_T_MAX is not an integer constant expression'
updated_at = <Date 2022-02-06.21:37:17.876>
user = 'https://bugs.python.org/ov2k'

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activity = <Date 2022-02-06.21:37:17.876>
actor = 'ov2k'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2022-02-06.21:20:42.705>
creator = 'ov2k'
dependencies = []
files = []
hgrepos = []
issue_num = 46664
keywords = []
message_count = 1.0
messages = ['412670']
nosy_count = 1.0
nosy_names = ['ov2k']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue46664'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']

[ov2k]

PY_SSIZE_T_MAX is currently defined in Include/pyport.h as:

#define PY_SSIZE_T_MAX ((Py_ssize_t)(((size_t)-1)>>1))

This is not an integer constant expression, which means it can't be used in preprocessor conditionals. For example:

#if PY_SSIZE_T_MAX > UINT32_MAX

will fail to compile. This was touched upon and ignored a long time ago:

https://mail.python.org/archives/list/python-dev@python.org/thread/27X7LINL4UO7DAJE6J3IFQEZGUKAO4VL/

I think the best fix is to move the definition of PY_SSIZE_T_MAX (and PY_SSIZE_T_MIN) next to the definition of Py_ssize_t, and use the proper corresponding limit macro. If Py_ssize_t is a typedef for ssize_t, then PY_SSIZE_T_MAX should be SSIZE_MAX. If Py_ssize_t is a typedef for Py_intptr_t, then PY_SSIZE_T_MAX should be INTPTR_MAX. There's a minor complication because Py_ssize_t can be defined in PC/pyconfig.h. I'm not so familiar with the various Windows compilers, so I'm not sure what's best to do here. I think __int64 has a corresponding _I64_MAX macro, and int obviously has INT_MAX.