[PATCH v5] meson: work around broken system PCRE2 dependency in macOS

["Carlo Marcelo Arenas Belón" <carenas@gmail.com>]

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.

Detect that case and allow a fallback to a wrapped submodule
if the feature is enabled and that is possible, or print a
warning and disable the feature if the feature was set to "auto",
which is the new default.

To keep consistency with the cmake build system used on Windows,
add a special rule to re-enable the pcre2 feature there.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Suggested-by: Eli Schwartz <eschwartz@gentoo.org>
Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
---
 meson.build       | 25 ++++++++++++++++++++++++-
 meson_options.txt |  2 +-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/meson.build b/meson.build
index 596f5ac711..c77ce82bf2 100644
--- a/meson.build
+++ b/meson.build
@@ -1055,7 +1055,30 @@ else
   build_options_config.set('NO_ICONV', '1')
 endif
 
-pcre2 = dependency('libpcre2-8', required: get_option('pcre2'), default_options: ['default_library=static', 'test=false'])
+# can't use enable_auto_if() because it is only available in meson 1.1
+if host_machine.system() == 'windows' and get_option('pcre2').allowed()
+  pcre2_feature = true
+else
+  pcre2_feature = get_option('pcre2')
+endif
+pcre2 = dependency('libpcre2-8', required: pcre2_feature, default_options: ['default_library=static', 'test=false'])
+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 pcre2_feature.enabled()
+      # Attempt to fallback, method can't be pkg-config 
+      pcre2 = dependency('libpcre2-8', method: 'builtin', default_options: ['default_library=static', 'test=false'])
+      if not pcre2.found()
+        error('only a broken pcre2 install found and pcre2 is required')
+      endif
+    else
+      # Replace with not-found-dependency
+      pcre2 = dependency('', required: false)
+      warning('broken pcre2 install found, disabling pcre2 feature')
+    endif
+  endif
+endif
+
 if pcre2.found()
   libgit_dependencies += pcre2
   libgit_c_args += '-DUSE_LIBPCRE2'
diff --git a/meson_options.txt b/meson_options.txt
index e7f768df24..1668f260a1 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',
   description: 'Support Perl-compatible regular expressions in e.g. git-grep(1).')
 option('perl', type: 'feature', value: 'auto',
   description: 'Build tools written in Perl.')
-- 
2.39.5 (Apple Git-154)