Compiling timemodule.c can fail on macOS due to availability warnings

[MaximeBelanger]

BPO	35025
Nosy	@ronaldoussoren, @vstinner, @benjaminp, @ned-deily, @miss-islington
PRs	bpo-35025: Properly guard the CLOCK_GETTIME et al macros in timemodule.c #9961 [3.7] closes bpo-35025: Properly guard the CLOCK_GETTIME et al macros in timemodule.c. (GH-9961) #10019 [3.6] closes bpo-35025: Properly guard the CLOCK_GETTIME et al macros in timemodule.c. (GH-9961) #10020

^{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 2018-10-21.00:08:00.648>
created_at = <Date 2018-10-19.06:24:57.716>
labels = ['extension-modules', 'OS-mac', '3.8', 'build', '3.7']
title = 'Compiling `timemodule.c` can fail on macOS due to availability warnings'
updated_at = <Date 2018-10-21.00:41:45.409>
user = 'https://bugs.python.org/MaximeBelanger'

bugs.python.org fields:

activity = <Date 2018-10-21.00:41:45.409>
actor = 'miss-islington'
assignee = 'none'
closed = True
closed_date = <Date 2018-10-21.00:08:00.648>
closer = 'benjamin.peterson'
components = ['Extension Modules', 'macOS']
creation = <Date 2018-10-19.06:24:57.716>
creator = 'Maxime Belanger'
dependencies = []
files = []
hgrepos = []
issue_num = 35025
keywords = ['patch']
message_count = 4.0
messages = ['328030', '328183', '328184', '328185']
nosy_count = 6.0
nosy_names = ['ronaldoussoren', 'vstinner', 'benjamin.peterson', 'ned.deily', 'Maxime Belanger', 'miss-islington']
pr_nums = ['9961', '10019', '10020']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue35025'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[MaximeBelanger]

We build Python on macOS with -Werror=unguarded-availability and -mmacosx-version-min=<xx> to ensure libpython is binary-compatible with earlier versions of macOS.

This can create problems when building some modules, including timemodule.c, which was recently altered to fix bpo-28081. The initial fix is inappropriate, because attempting to reference CLOCK_REALTIME et al when HAVE_CLOCK_GETTIME is unset (in our case, due to being too "new"), results in a compiler error:

./Modules/timemodule.c:1368:29: error: '_CLOCK_REALTIME' is only available on macOS 10.12 or newer
      [-Werror,-Wunguarded-availability]
    PyModule_AddIntMacro(m, CLOCK_REALTIME);
                            ^~~~~~~~~~~~~~
/usr/include/time.h:154:24: note: expanded from macro 'CLOCK_REALTIME'
#define CLOCK_REALTIME _CLOCK_REALTIME
                       ^~~~~~~~~~~~~~~
./Include/modsupport.h:78:67: note: expanded from macro 'PyModule_AddIntMacro'
#define PyModule_AddIntMacro(m, c) PyModule_AddIntConstant(m, #c, c)

A more correct patch (I'm attaching ours) is to only add the macros to the module if at least one of the three functions is defined. This should continue to work for the author of the original issue as well as fix our problem.

[benjaminp]

New changeset 9445118 by Benjamin Peterson (Max Bélanger) in branch 'master':
closes bpo-35025: Properly guard the CLOCK_GETTIME et al macros in timemodule.c. (GH-9961)
9445118

[miss-islington]

New changeset beb83d0 by Miss Islington (bot) in branch '3.6':
closes bpo-35025: Properly guard the CLOCK_GETTIME et al macros in timemodule.c. (GH-9961)
beb83d0

[miss-islington]

New changeset 002aef3 by Miss Islington (bot) in branch '3.7':
closes bpo-35025: Properly guard the CLOCK_GETTIME et al macros in timemodule.c. (GH-9961)
002aef3