Add constantness to PyStructSequence_UnnamedField

[serhiy-storchaka]

BPO	38650
Nosy	@ericsnowcurrently, @serhiy-storchaka, @corona10
PRs	bpo-38650: Constify PyStructSequence_UnnamedField. #17005

^{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 2019-11-16.17:22:45.452>
created_at = <Date 2019-10-30.20:01:43.091>
labels = ['interpreter-core', '3.9']
title = 'Add constantness to PyStructSequence_UnnamedField'
updated_at = <Date 2019-11-22.19:51:57.606>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2019-11-22.19:51:57.606>
actor = 'eric.snow'
assignee = 'none'
closed = True
closed_date = <Date 2019-11-16.17:22:45.452>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2019-10-30.20:01:43.091>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 38650
keywords = ['patch']
message_count = 4.0
messages = ['355731', '356755', '356757', '357318']
nosy_count = 3.0
nosy_names = ['eric.snow', 'serhiy.storchaka', 'corona10']
pr_nums = ['17005']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue38650'
versions = ['Python 3.9']

[serhiy-storchaka]

Currently the variable PyStructSequence_UnnamedField has type "char *". It is used as a special value for setting to the name field of PyStructSequence_Field. But the type of the name field is "const char *".

I propose to change the declaration of PyStructSequence_UnnamedField to "const char * const". Makes it referring to immutable character string and make it itself immutable.

It is binary compatible change, but some user code can complain at compilation time if it uses PyStructSequence_UnnamedField in unusual way (assigns to the "char *" variable, etc). It is very unlikely.

[serhiy-storchaka]

New changeset bd44a7e by Serhiy Storchaka in branch 'master':
bpo-38650: Constify PyStructSequence_UnnamedField. (GH-17005)
bd44a7e

[corona10]

Looks like

cpython/Tools/c-analyzer/known.tsv

Line 1549 in 088b63e

Objects/structseq.c - PyStructSequence_UnnamedField variable char *PyStructSequence_UnnamedField

should be updated also.
What do you think?

[ericsnowcurrently]

I wouldn't worry about the c-analyzer stuff for now. I plan on re-generating the file in the near future.