Warning: implicit declaration of function '_setmode'

[ma8ma]

BPO	28768
Nosy	@pfmoore, @vstinner, @tjguk, @benjaminp, @vadmium, @zware, @zooba, @ma8ma
PRs	[Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Files	include-io.h.patch 2.7-include-io.h.patch

^{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 2017-01-04.16:00:39.202>
created_at = <Date 2016-11-21.20:00:30.849>
labels = ['build', '3.7', 'OS-windows']
title = "Warning: implicit declaration of function '_setmode'"
updated_at = <Date 2017-03-31.16:36:34.322>
user = 'https://github.com/ma8ma'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:34.322>
actor = 'dstufft'
assignee = 'none'
closed = True
closed_date = <Date 2017-01-04.16:00:39.202>
closer = 'vstinner'
components = ['Build', 'Windows']
creation = <Date 2016-11-21.20:00:30.849>
creator = 'masamoto'
dependencies = []
files = ['45592', '45593']
hgrepos = []
issue_num = 28768
keywords = ['patch']
message_count = 9.0
messages = ['281389', '281470', '281472', '284210', '284211', '284566', '284616', '284645', '284646']
nosy_count = 10.0
nosy_names = ['paul.moore', 'vstinner', 'tim.golden', 'benjamin.peterson', 'stutzbach', 'python-dev', 'martin.panter', 'zach.ware', 'steve.dower', 'masamoto']
pr_nums = ['552']
priority = 'normal'
resolution = 'fixed'
stage = 'commit review'
status = 'closed'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue28768'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7']

[ma8ma]

Platform that appeared warning is Vista Cygwin x86. Interpreter execution doesn't crash because _setmode function is supplied from cygwin1.dll that always linked.
Warning reason is header io.h [*] doesn't include to source file. Therefore I wrote two patches for 3.7 and 2.7.

[*] https://msdn.microsoft.com/en-us/library/tw4k6df8.aspx (Cygwin also avaliable)

build log on 3.7:

gcc -c -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I. -I./Include -DPy_BUILD_CORE -o Modules/main.o Modules/main.c
Modules/main.c: In function 'Py_Main':
Modules/main.c:599:5: warning: implicit declaration of function '_setmode' [-Wimplicit-function-declaration]
_setmode(fileno(stdin), O_BINARY);
^
gcc -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I. -I./Include -DPy_BUILD_CORE -I./Modules/_io -c ./Modules/_io/fileio.c -o Modules/fileio.o
./Modules/_io/fileio.c: In function '_io_FileIO___init___impl':
./Modules/_io/fileio.c:478:5: warning: implicit declaration of function '_setmode' [-Wimplicit-function-declaration]
_setmode(self->fd, O_BINARY);
^

[vadmium]

The Modules/main.c change at least looks reasonable as a bug fix.

In the long term, it would be nice to clean up some of the conditions for including <io.h>. Currently it is unconditional via PC/pyconfig.h, configure.ac optionally enables HAVE_IO_H, and there are various other conditions in different files, like as QUICKWIN, PYCC_VACPP and MS_WINDOWS || __CYGWIN__.

[vstinner]

include-io.h.patch LGTM.

2.7-include-io.h.patch: Cygwin is not currently officially supported in CPython. I suggest to focus efforts on supporting Cygwin in the default branch (future 3.7) only, as we are doing with Android.

[python-dev]

New changeset 5027780d456b by Steve Dower in branch '3.6':
Issue bpo-28768: Fix implicit declaration of function _setmode. Patch by Masayuki Yamamoto
https://hg.python.org/cpython/rev/5027780d456b

New changeset 276d1bae92be by Steve Dower in branch 'default':
Issue bpo-28768: Fix implicit declaration of function _setmode. Patch by Masayuki Yamamoto
https://hg.python.org/cpython/rev/276d1bae92be

[zooba]

I applied to 3.6 and default. If anyone is motivated enough to apply to 2.7, feel free.

[vstinner]

Masayuki Yamamoto: Do you consider that Python 2.7 should be fixed as well? What is your use case for compiling Python 2.7 on Windows using Cygwin?

[ma8ma]

Building 2.7 is for testing purposes. It is used to judge whether it is a problem (specifically for Cygwin-specific) originated in the old version. _setmode is an important function for setting input and output of CPython, so in Cygwin I feel annoying that warnings are issued even though there is actually no problem.

[python-dev]

New changeset 5ea0fef6ec53 by Steve Dower in branch '2.7':
Issue bpo-28768: Fix implicit declaration of function _setmode. Patch by Masayuki Yamamoto
https://hg.python.org/cpython/rev/5ea0fef6ec53

[vstinner]

Well, the change is not going to hurt. I backported the change. Thanks for the fix Masayuki!