Deprecate building with bundled copy of libffi on non-Darwin POSIX platforms

[zware]

BPO	27976
Nosy	@malemburg, @doko42, @tjguk, @ned-deily, @bitdancer, @meadori, @cjerdonek, @xdegaye, @berkerpeksag, @zware, @koobs, @zooba, @yan12125
Files	deprecate_bundled_libffi.diff issue27976.diff

^{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 2016-09-10.00:01:35.487>
created_at = <Date 2016-09-06.17:56:22.387>
labels = ['ctypes', 'type-feature', 'build']
title = 'Deprecate building with bundled copy of libffi on non-Darwin POSIX platforms'
updated_at = <Date 2016-09-10.00:01:35.485>
user = 'https://github.com/zware'

bugs.python.org fields:

activity = <Date 2016-09-10.00:01:35.485>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2016-09-10.00:01:35.487>
closer = 'python-dev'
components = ['Build', 'ctypes']
creation = <Date 2016-09-06.17:56:22.387>
creator = 'zach.ware'
dependencies = []
files = ['44399', '44455']
hgrepos = []
issue_num = 27976
keywords = ['patch']
message_count = 6.0
messages = ['274576', '274627', '274628', '274761', '274926', '275504']
nosy_count = 17.0
nosy_names = ['lemburg', 'doko', 'tim.golden', 'ned.deily', 'Arfrever', 'r.david.murray', 'meador.inge', 'chris.jerdonek', 'xdegaye', 'python-dev', 'berker.peksag', 'zach.ware', 'koobs', 'steve.dower', 'gustavotemple', 'fabiovmp', 'yan12125']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27976'
versions = ['Python 3.6']

[zware]

Nosy list copied from bpo-23085.

Here's a patch that deprecates building _ctypes with the bundled copy of libffi (Modules/_ctypes/libffi/). The default on all platforms (other than Windows) is now to use a system copy of libffi; use the '--without-system-ffi' flag to ./configure to use the bundled copy. On non-Darwin platforms, a warning will be emitted noting that Modules/_ctypes/libffi will not be distributed with 3.7.

[berkerpeksag]

+1, thanks for working on this!

Two questions:

1. Should we check the system version of libffi and warn users (and probably use the bundled version for now) if it was older than 3.1?

2. I know this isn't directly a user-facing feature, but should we add a short note to Doc/whatsnew/3.6.rst? (we can probably mention that most of the Linux distributions already use --with-system-ffi.)

[zware]

I don't think it's worthwhile to do a version check and warning, especially since we'll be removing the bundled version in 3.7. A docs note is worthwhile, though, I'll attach a new patch shortly.

[yan12125]

That's great! bpo-26942 can be closed after this change is landed. It's caused by a libffi bug on Android.

[zware]

Finally got a new patch created. After talking it over with Ned yesterday, this patch makes sure that nothing changes on OSX.

[python-dev]

New changeset 3e02187e50df by Zachary Ware in branch 'default':
Closes bpo-27976: Deprecate bundled full copy of libffi
https://hg.python.org/cpython/rev/3e02187e50df