Re: [PATCH v3] meson: disable PCRE2 dependency by default in macOS
From: Eli Schwartz <hidden>
Date: 2025-07-15 01:55:31
On 7/13/25 1:48 PM, Carlo Marcelo Arenas Belón wrote:
Makefile requires the user to provide the USE_LIBPCRE2 flag to enable this dependency, but meson has it enabled by default, which can be problematic, at least in macOS. macOS provides a PCRE2 library in base that is not usable and not configured properly, as it installs a pkgconf module that points to a non existent pcre2.h header in /usr/local/include. Add an option that will need to be turned to true once an alternative PCRE2 library is installed (which hopefully provides its own pkgconf module earlier in PKG_CONFIG_PATH) or meson has been instructed to use its subproject as a suitable dependency by `--force-fallback-for=pcre2`.
I cannot possibly agree with any part of this. Right bug report, wrong patch. Problem: Meson supports three modes: - require pcre2 and fail if missing - automatically, optimistically use it if possible - disable and reject it even if available macOS has a problem: - pcre2 (in modes 1 and 2) is detected as available via a system package, but upon successfully configuring a ninja file, the compile fails Solution proposed here: - v1: switch default mode from "enabled" to "disabled", leaving feature broken if anyone tries it out - v2 / v3: switch default mode from "enabled" to "auto", then ignoring the config setting by default, and permitting users to use an ugly "are you sure" option to get... a failing build. Nowhere are we checking what we got. Trying to build with pcre2 will fail in confusingly awkward ways at the worst time: compile time. We don't need a build option here to ask for this bad experience -- we should just get it correct. :) The goal should be, if the pcre2 feature is: - enabled, meson should *fail early* if the demand cannot be met, providing a clear explanation of what is wrong - auto, meson should *detect* it cannot work and build without it
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Signed-off-by: Carlo Marcelo Arenas Belón <redacted> --- meson.build | 3 ++- meson_options.txt | 4 +++- 2 files changed, 5 insertions(+), 2 deletions(-)diff --git a/meson.build b/meson.build index 7fea4a34d6..e1475be6c8 100644 --- a/meson.build +++ b/meson.build@@ -1055,7 +1055,8 @@ else build_options_config.set('NO_ICONV', '1') endif -pcre2 = dependency('libpcre2-8', required: get_option('pcre2'), default_options: ['default_library=static', 'test=false']) +pcre2_feature = get_option('pcre2').disable_auto_if(host_machine.system() == 'darwin' and not get_option('macos_workaround_system_pcre2')) +pcre2 = dependency('libpcre2-8', required: pcre2_feature, default_options: ['default_library=static', 'test=false']) if pcre2.found() libgit_dependencies += pcre2 libgit_c_args += '-DUSE_LIBPCRE2'
Instead of disable_auto_if, we should simply verify a working install.
if pcre2.found() and pcre2.type_name() != 'internal' and
host_machine.system() == 'darwin'
# macOS installs a broken system package, double check
if not compiler.has_header('pcre2.h', dependencies: pcre2)
if get_option('pcre2').enabled()
error('broken pcre2 install found but pcre2 is required')
endif
# Replace with not-found-dependency
pcre2 = dependency('', required: false)
warning('broken pcre2 install found, disabling pcre2 feature')
endif
endif
if pcre2.found()
libgit_dependencies += pcre2
[...]
Please double-check my work, that this compiler.has_header() is
sufficient on your reproducer system to detect and disable the
non-working feature.
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diff --git a/meson_options.txt b/meson_options.txt index e7f768df24..f63ff32556 100644 --- a/meson_options.txt +++ b/meson_options.txt@@ -45,7 +45,7 @@ option('gitweb', type: 'feature', value: 'auto', description: 'Build Git web interface. Requires Perl.') option('iconv', type: 'feature', value: 'auto', description: 'Support reencoding strings with different encodings.') -option('pcre2', type: 'feature', value: 'enabled', +option('pcre2', type: 'feature', value: 'auto',
This part is fine. We shouldn't default-fail if it isn't found, when we can't expect it to be universally available.
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description: 'Support Perl-compatible regular expressions in e.g. git-grep(1).') option('perl', type: 'feature', value: 'auto', description: 'Build tools written in Perl.')@@ -73,6 +73,8 @@ option('breaking_changes', type: 'boolean', value: false, description: 'Enable upcoming breaking changes.') option('macos_use_homebrew_gettext', type: 'boolean', value: true, description: 'Use gettext from Homebrew instead of the slightly-broken system-provided one.') +option('macos_workaround_system_pcre2', type: 'boolean', value: false, + description: 'A working PCRE2 library is available or will be provided by a subproject.') # gitweb configuration. option('gitweb_config', type: 'string', value: 'gitweb_config.perl')
-- Eli Schwartz
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