[C API] PyUnicode_CHECK_INTERNED() doesn't work in the limited C API

[vstinner]

BPO	46007
Nosy	@vstinner, @encukou, @miss-islington
PRs	bpo-46007: Exclude PyUnicode_CHECK_INTERNED() from limited C API #29987

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-12-09.09:00:19.225>
created_at = <Date 2021-12-07.17:34:25.875>
labels = ['expert-C-API', '3.9', '3.10', '3.11']
title = "[C API] PyUnicode_CHECK_INTERNED() doesn't work in the limited C API"
updated_at = <Date 2021-12-09.09:00:19.224>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2021-12-09.09:00:19.224>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2021-12-09.09:00:19.225>
closer = 'vstinner'
components = ['C API']
creation = <Date 2021-12-07.17:34:25.875>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 46007
keywords = ['patch']
message_count = 3.0
messages = ['407955', '408007', '408086']
nosy_count = 3.0
nosy_names = ['vstinner', 'petr.viktorin', 'miss-islington']
pr_nums = ['29987']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue46007'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[vstinner]

The PyUnicode_CHECK_INTERNED() macro uses the PyASCIIObject structure which is *excluded* from the limited C API:

/* Use only if you know it's a string */
#define PyUnicode_CHECK_INTERNED(op) \
    (((PyASCIIObject *)(op))->state.interned)

Using this macro in the limited C API doesn't work.

I propose to remove it from the limited C API.

IMO it's not a good idea to fix the function in the limited C API by converting it to a regular function hiding the implementation details and so working at the ABI level. We should not expose such "implementation detail" (if a string is "interned or not") in the *limited* C API.

[encukou]

+1, PyUnicodeObject/PyASCIIObject is excluded from the limited API since Python 3.2, so it wasn't possible to use this macro.

[miss-islington]

New changeset 73325bb by Victor Stinner in branch 'main':
bpo-46007: Exclude PyUnicode_CHECK_INTERNED() from limited C API (GH-29987)
73325bb