pyconfig.h macro "timezone" name clashes with user source are likely

[mikofski]

BPO	34657
Nosy	@pfmoore, @tjguk, @zware, @zooba, @mikofski
Superseder	bpo-24643: VS 2015 pyconfig.h #define timezone _timezone conflicts with timeb.h

^{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 2018-09-13.14:40:35.355>
created_at = <Date 2018-09-13.06:10:52.349>
labels = ['3.8', 'type-feature', '3.7', 'OS-windows']
title = 'pyconfig.h macro "timezone" name clashes with user source are likely'
updated_at = <Date 2018-09-13.14:40:35.353>
user = 'https://github.com/mikofski'

bugs.python.org fields:

activity = <Date 2018-09-13.14:40:35.353>
actor = 'zach.ware'
assignee = 'none'
closed = True
closed_date = <Date 2018-09-13.14:40:35.355>
closer = 'zach.ware'
components = ['Windows']
creation = <Date 2018-09-13.06:10:52.349>
creator = 'bwanamarko'
dependencies = []
files = []
hgrepos = []
issue_num = 34657
keywords = []
message_count = 2.0
messages = ['325235', '325249']
nosy_count = 5.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'steve.dower', 'bwanamarko']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '24643'
type = 'enhancement'
url = 'https://bugs.python.org/issue34657'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7', 'Python 3.8']

[mikofski]

TL;DR: if PC user compiles source which defines "timezone" in a header, and includes Python.h after the header, then the macro also called "timezone" in pyconfig.h will redefine the users source, yielding unexpected results.

see Cython google group for an actual use case where this occurred:
https://groups.google.com/forum/#!topic/cython-users/pjbhYrpl_rU

trying to compile NREL SPA code which has a header file with a struct with a timezone field fails with the following traceback:
spa.h(88): error C2032: '__timezone': function cannot be member of struct '<anonymous-tag>'

here's the macro in PC/pyconfig.h in master as of 5489bda

cpython/PC/pyconfig.h

Line 202 in 5489bda

#define timezone _timezone

/* VS 2015 defines these names with a leading underscore */
#if _MSC_VER >= 1900
#define timezone _timezone
#define daylight _daylight
#define tzname _tzname
#endif

[zware]

This is a duplicate of bpo-24643.