Improve and simplify configure.ac checks

[tiran]

BPO	45723
Nosy	@tiran, @erlend-aasland
PRs	Details bpo-45723: Add helper macros and more caching to configure.ac (GH-29429) #29429 bpo-45723: Prepare support for autoconf 2.71 (GH-29441) #29441 bpo-45723: Detect missing pkg-config (GH-29442) #29442 bpo-45723: Add macro for disabling/enabling CC warnings (GH-29466) #29466 bpo-45723: Improve and simplify more configure.ac checks (GH-29485) #29485 bpo-45723: Remove obsolete AC_EXEEXT from configure.ac #29486 bpo-45723: Remove dead code for obsolete --with-dyld option #29500 bpo-45723: Add --with-pkg-config to configure (GH-29517) #29517 bpo-45723: Add helpers for save/restore env (GH-29637) #29637 bpo-45723: Use SAVE/RESTORE macros in configure.ac #29701 bpo-45723: Sort the grand AC_CHECK_HEADERS check #29846 bpo-45723: Normalise configure user communication (GH-30024) #30024 bpo-89886: Clean up MACHDEP and _PYTHON_HOST_PLATFORM checks #30026 gh-89886: Use AC_CHECK_TYPES iso. AC_CHECK_TYPE #30029 bpo-45723: Fix detection of epoll #30449

^{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 = 'https://github.com/tiran'
closed_at = None
created_at = <Date 2021-11-05.10:05:47.030>
labels = ['type-feature', 'build', '3.11']
title = 'Improve and simplify configure.ac checks'
updated_at = <Date 2022-01-12.04:40:54.295>
user = 'https://github.com/tiran'

bugs.python.org fields:

activity = <Date 2022-01-12.04:40:54.295>
actor = 'zach.ware'
assignee = 'christian.heimes'
closed = False
closed_date = None
closer = None
components = ['Build']
creation = <Date 2021-11-05.10:05:47.030>
creator = 'christian.heimes'
dependencies = []
files = []
hgrepos = []
issue_num = 45723
keywords = ['patch']
message_count = 18.0
messages = ['405780', '405799', '405865', '405896', '405932', '405977', '405978', '406021', '406027', '406054', '406104', '406137', '406745', '407281', '408191', '409946', '409951', '409953']
nosy_count = 3.0
nosy_names = ['christian.heimes', 'erlendaasland', 'byllyfish']
pr_nums = ['29429', '29441', '29442', '29466', '29485', '29486', '29500', '29517', '29637', '29701', '29846', '30024', '30026', '30029', '30449']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45723'
versions = ['Python 3.11']

Linked PRs

• bpo-45723: Add helper macros and more caching to configure.ac (GH-29429) #29429
• bpo-45723: Prepare support for autoconf 2.71 (GH-29441) #29441
• bpo-45723: Detect missing pkg-config (GH-29442) #29442
• bpo-45723: Add macro for disabling/enabling CC warnings (GH-29466) #29466
• bpo-45723: Improve and simplify more configure.ac checks (GH-29485) #29485
• bpo-45723: Remove obsolete AC_EXEEXT from configure.ac #29486
• bpo-45723: Remove dead code for obsolete --with-dyld option #29500
• bpo-45723: Add --with-pkg-config to configure (GH-29517) #29517
• bpo-45723: Add helpers for save/restore env (GH-29637) #29637
• bpo-45723: Use SAVE/RESTORE macros in configure.ac #29701
• bpo-45723: Sort the grand AC_CHECK_HEADERS check #29846
• bpo-45723: Normalise configure user communication (GH-30024) #30024
• bpo-89886: Clean up MACHDEP and _PYTHON_HOST_PLATFORM checks #30026
• gh-89886: Use AC_CHECK_TYPES iso. AC_CHECK_TYPE #30029
• bpo-45723: Fix detection of epoll #30449
• GH-89886: Bump autoconf to version 2.71 #104925
• gh-89886: Rely on HAVE_SYS_TIME_H #105058
• gh-89886: Properly quote Autoconf macro arguments #105062
• [3.12] gh-89886: Properly quote Autoconf macro arguments (#105062) #105118
• [3.12] gh-89886: Rely on HAVE_SYS_TIME_H (GH-105058) #105192
• [3.12] GH-89886: Bump to GNU Autoconf v2.71 (#104925) #105207
• gh-89886: Use Autoconf quadrigraphs where appropriate #105226
• [3.12] gh-89886: Use Autoconf quadrigraphs where appropriate (#105226) #105423

[tiran]

The autoconf-based build system has room for improvements. The configure.ac script can be simplified in several places by using AS and AC macros or by defining new custom macros.

For example we have a lot of blocks that look like this:

AC_MSG_CHECKING(for chroot)
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>]], [[void x=chroot]])],
 [AC_DEFINE(HAVE_CHROOT, 1, Define if you have the 'chroot' function.)
 AC_MSG_RESULT(yes)],
 [AC_MSG_RESULT(no)
])

The block has an issue, too. It does not use AC_CACHE to cache the result. The entire block can be replaced by a custom macro that takes care of everything and implements correct caching:

 PY_CHECK_FUNC([chroot], [#include <unistd.h>])

We can also move several library and header checks from setup.py into configure.ac, e.g. check for soundcard.h or gdbm libs and headers.

[tiran]

The first PR adds helper macros, AC_CACHE_CHECK() [1] and AS_VAR_IF() [2]. It also unified internal variables to use format "ac_cv_func_$funcname", "ac_cv_func_lib_$library_$funcname", or "ac_cv_header_$headername_h". "ac_cv" stands for autoconf cached value.

AC_CACHE_CHECK() replaces AC_MSG_CHECKING() and AC_MSG_RESULT(). The syntax is AC_CACHE_CHECK([text], [cache variable], [body]) where body is only excecuted when the cache variable is not set. The body has to set the cache variable to yes or no. Any output and AC_DEFINE must occur outside the body.

AS_VAR_IF() is a nicer way to write if test $variable = value; then; fi.

[1] https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Caching-Results.html#Caching-Results
[2] https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Polymorphic-Variables.html

[tiran]

#73627 introduces forward compatibility issues with autoconf 2.71. I took the output of autoupdate and resolved all warnings.

[tiran]

New changeset be3cd5c by Christian Heimes in branch 'main':
bpo-45723: Detect missing pkg-config (GH-29442)
be3cd5c

[tiran]

New changeset 57c50c9 by Christian Heimes in branch 'main':
bpo-45723: Add helper macros and more caching to configure.ac (GH-29429)
57c50c9

[tiran]

New changeset 9bd0cf5 by Erlend Egeberg Aasland in branch 'main':
bpo-45723: Add macro for disabling/enabling CC warnings (GH-29466)
9bd0cf5

[tiran]

New changeset cbab997 by Christian Heimes in branch 'main':
bpo-45723: Prepare support for autoconf 2.71 (GH-29441)
cbab997