Re: [PATCH 7/8] meson: compile compatibility sources separately

[Phillip Wood <phillip.wood123@gmail.com>]

On 11/03/2026 14:32, Phillip Wood wrote:
> On 10/03/2026 17:52, Patrick Steinhardt wrote:
>> In the next commit we're about to introduce a precompiled header for
>> "git-compat-util.h". The consequence of this change is that we'll
>> implicitly include that header for every compilation unit that uses the
>> precompiled headers.
> 
> Is that a meson thing? I know it defines precompiled headers on a per- 
> target basis but does it somehow force each source file to include the 
> precompiled header? Looking at the gcc documentation it seems like the 
> precompiled header is only included where the original header is 
> included.

Answering my own question the precompiled header is included via 
"-include" on the commandline. This is necessary in the general case 
because a precompiled header cannot be used once the first C token is seen.

As an aside in git we could probably get away without using "-include" 
because if we include "git-compat-util.h" it is always the first thing 
we do, or we inculde another file like "builtin.h" which immediately 
includes "git-compat-util.h" and so it is included before the first C 
token is seen. However meson cannot rely on that.

I notice the reftable sources don't seem to include "git-compat-util.h", 
do they need special handling here as well?

Thanks

Phillip

> Splitting out the sources that do not depend on "git-compat- 
> util.h" does mean we get some additional parallelism while we're 
> precompiling the header which is probably a good thing.
> 
> Thanks
> 
> Phillip
> 
>> This is okay for our "normal" library sources and our builtins. But some
>> of our compatibility sources do not include the header on purpose, and
>> doing so would cause compileir errors.
>>
>> Prepare for this change by splitting out compatibility sources into
>> their static library. Like this we can selectively enable precompiled
>> headers for the library sources.
>>
>> Signed-off-by: Patrick Steinhardt <ps@pks.im>
>> ---
>>   meson.build | 79 ++++++++++++++++++++++++++++++++++ 
>> +--------------------------
>>   1 file changed, 45 insertions(+), 34 deletions(-)
>>
>> diff --git a/meson.build b/meson.build
>> index 604fe89d2d..cd00be1c23 100644
>> --- a/meson.build
>> +++ b/meson.build
>> @@ -271,6 +271,13 @@ version_gen_environment.set('GIT_VERSION', 
>> get_option('version'))
>>   compiler = meson.get_compiler('c')
>> +compat_sources = [
>> +  'compat/nonblock.c',
>> +  'compat/obstack.c',
>> +  'compat/open.c',
>> +  'compat/terminal.c',
>> +]
>> +
>>   libgit_sources = [
>>     'abspath.c',
>>     'add-interactive.c',
>> @@ -304,10 +311,6 @@ libgit_sources = [
>>     'commit.c',
>>     'common-exit.c',
>>     'common-init.c',
>> -  'compat/nonblock.c',
>> -  'compat/obstack.c',
>> -  'compat/open.c',
>> -  'compat/terminal.c',
>>     'compiler-tricks/not-constant.c',
>>     'config.c',
>>     'connect.c',
>> @@ -1163,7 +1166,7 @@ endif
>>   if not has_poll_h and not has_sys_poll_h
>>     libgit_c_args += '-DNO_POLL'
>> -  libgit_sources += 'compat/poll/poll.c'
>> +  compat_sources += 'compat/poll/poll.c'
>>     libgit_include_directories += 'compat/poll'
>>   endif
>> @@ -1179,7 +1182,7 @@ endif
>>   # implementation to threat things like drive prefixes specially.
>>   if host_machine.system() == 'windows' or not 
>> compiler.has_header('libgen.h')
>>     libgit_c_args += '-DNO_LIBGEN_H'
>> -  libgit_sources += 'compat/basename.c'
>> +  compat_sources += 'compat/basename.c'
>>   endif
>>   if compiler.has_header('paths.h')
>> @@ -1209,7 +1212,7 @@ if host_machine.system() != 'windows'
>>     foreach symbol : ['inet_ntop', 'inet_pton', 'hstrerror']
>>       if not compiler.has_function(symbol, dependencies: 
>> networking_dependencies)
>>         libgit_c_args += '-DNO_' + symbol.to_upper()
>> -      libgit_sources += 'compat/' + symbol + '.c'
>> +      compat_sources += 'compat/' + symbol + '.c'
>>       endif
>>     endforeach
>>   endif
>> @@ -1251,18 +1254,18 @@ else
>>   endif
>>   if host_machine.system() == 'darwin'
>> -  libgit_sources += 'compat/precompose_utf8.c'
>> +  compat_sources += 'compat/precompose_utf8.c'
>>     libgit_c_args += '-DPRECOMPOSE_UNICODE'
>>     libgit_c_args += '-DPROTECT_HFS_DEFAULT'
>>   endif
>>   # Configure general compatibility wrappers.
>>   if host_machine.system() == 'cygwin'
>> -  libgit_sources += [
>> +  compat_sources += [
>>       'compat/win32/path-utils.c',
>>     ]
>>   elif host_machine.system() == 'windows'
>> -  libgit_sources += [
>> +  compat_sources += [
>>       'compat/winansi.c',
>>       'compat/win32/dirent.c',
>>       'compat/win32/flush.c',
>> @@ -1289,20 +1292,20 @@ elif host_machine.system() == 'windows'
>>     libgit_include_directories += 'compat/win32'
>>     if compiler.get_id() == 'msvc'
>>       libgit_include_directories += 'compat/vcbuild/include'
>> -    libgit_sources += 'compat/msvc.c'
>> +    compat_sources += 'compat/msvc.c'
>>     else
>> -    libgit_sources += 'compat/mingw.c'
>> +    compat_sources += 'compat/mingw.c'
>>     endif
>>   endif
>>   if host_machine.system() == 'linux'
>> -  libgit_sources += 'compat/linux/procinfo.c'
>> +  compat_sources += 'compat/linux/procinfo.c'
>>   elif host_machine.system() == 'windows'
>> -  libgit_sources += 'compat/win32/trace2_win32_process_info.c'
>> +  compat_sources += 'compat/win32/trace2_win32_process_info.c'
>>   elif host_machine.system() == 'darwin'
>> -  libgit_sources += 'compat/darwin/procinfo.c'
>> +  compat_sources += 'compat/darwin/procinfo.c'
>>   else
>> -  libgit_sources += 'compat/stub/procinfo.c'
>> +  compat_sources += 'compat/stub/procinfo.c'
>>   endif
>>   if host_machine.system() == 'cygwin' or host_machine.system() == 
>> 'windows'
>> @@ -1315,13 +1318,13 @@ endif
>>   # Configure the simple-ipc subsystem required fro the fsmonitor.
>>   if host_machine.system() == 'windows'
>> -  libgit_sources += [
>> +  compat_sources += [
>>       'compat/simple-ipc/ipc-shared.c',
>>       'compat/simple-ipc/ipc-win32.c',
>>     ]
>>     libgit_c_args += '-DSUPPORTS_SIMPLE_IPC'
>>   else
>> -  libgit_sources += [
>> +  compat_sources += [
>>       'compat/simple-ipc/ipc-shared.c',
>>       'compat/simple-ipc/ipc-unix-socket.c',
>>     ]
>> @@ -1339,7 +1342,7 @@ if fsmonitor_backend != ''
>>     libgit_c_args += '-DHAVE_FSMONITOR_DAEMON_BACKEND'
>>     libgit_c_args += '-DHAVE_FSMONITOR_OS_SETTINGS'
>> -  libgit_sources += [
>> +  compat_sources += [
>>       'compat/fsmonitor/fsm-health-' + fsmonitor_backend + '.c',
>>       'compat/fsmonitor/fsm-ipc-' + fsmonitor_backend + '.c',
>>       'compat/fsmonitor/fsm-listen-' + fsmonitor_backend + '.c',
>> @@ -1355,7 +1358,7 @@ if not 
>> get_option('b_sanitize').contains('address') and get_option('regex').allo
>>     if compiler.get_define('REG_ENHANCED', prefix: '#include 
>> <regex.h>') != ''
>>       libgit_c_args += '-DUSE_ENHANCED_BASIC_REGULAR_EXPRESSIONS'
>> -    libgit_sources += 'compat/regcomp_enhanced.c'
>> +    compat_sources += 'compat/regcomp_enhanced.c'
>>     endif
>>   elif not get_option('regex').enabled()
>>     libgit_c_args += [
>> @@ -1364,7 +1367,7 @@ elif not get_option('regex').enabled()
>>       '-DNO_MBSUPPORT',
>>     ]
>>     build_options_config.set('NO_REGEX', '1')
>> -  libgit_sources += 'compat/regex/regex.c'
>> +  compat_sources += 'compat/regex/regex.c'
>>     libgit_include_directories += 'compat/regex'
>>   else
>>       error('Native regex support requested but not found')
>> @@ -1428,7 +1431,7 @@ else
>>     if get_option('b_sanitize').contains('address')
>>       libgit_c_args += '-DNO_MMAP'
>> -    libgit_sources += 'compat/mmap.c'
>> +    compat_sources += 'compat/mmap.c'
>>     else
>>       checkfuncs += { 'mmap': ['mmap.c'] }
>>     endif
>> @@ -1438,7 +1441,7 @@ foreach func, impls : checkfuncs
>>     if not compiler.has_function(func)
>>       libgit_c_args += '-DNO_' + func.to_upper()
>>       foreach impl : impls
>> -      libgit_sources += 'compat/' + impl
>> +      compat_sources += 'compat/' + impl
>>       endforeach
>>     endif
>>   endforeach
>> @@ -1449,13 +1452,13 @@ endif
>>   if not compiler.has_function('strdup')
>>     libgit_c_args += '-DOVERRIDE_STRDUP'
>> -  libgit_sources += 'compat/strdup.c'
>> +  compat_sources += 'compat/strdup.c'
>>   endif
>>   if not compiler.has_function('qsort')
>>     libgit_c_args += '-DINTERNAL_QSORT'
>>   endif
>> -libgit_sources += 'compat/qsort_s.c'
>> +compat_sources += 'compat/qsort_s.c'
>>   if compiler.has_function('getdelim')
>>     libgit_c_args += '-DHAVE_GETDELIM'
>> @@ -1511,7 +1514,7 @@ if meson.can_run_host_binaries() and 
>> compiler.run('''
>>     }
>>   ''', name: 'fread reads directories').returncode() == 0
>>     libgit_c_args += '-DFREAD_READS_DIRECTORIES'
>> -  libgit_sources += 'compat/fopen.c'
>> +  compat_sources += 'compat/fopen.c'
>>   endif
>>   if not meson.is_cross_build() and fs.exists('/dev/tty')
>> @@ -1745,14 +1748,22 @@ else
>>   endif
>>   libgit = declare_dependency(
>> -  link_with: static_library('git',
>> -    sources: libgit_sources,
>> -    c_args: libgit_c_args + [
>> -      '-DGIT_VERSION_H="' + version_def_h.full_path() + '"',
>> -    ],
>> -    dependencies: libgit_dependencies,
>> -    include_directories: libgit_include_directories,
>> -  ),
>> +  link_with: [
>> +    static_library('compat',
>> +      sources: compat_sources,
>> +      c_args: libgit_c_args,
>> +      dependencies: libgit_dependencies,
>> +      include_directories: libgit_include_directories,
>> +    ),
>> +    static_library('git',
>> +      sources: libgit_sources,
>> +      c_args: libgit_c_args + [
>> +        '-DGIT_VERSION_H="' + version_def_h.full_path() + '"',
>> +      ],
>> +      dependencies: libgit_dependencies,
>> +      include_directories: libgit_include_directories,
>> +    ),
>> +  ],
>>     compile_args: libgit_c_args,
>>     dependencies: libgit_dependencies,
>>     include_directories: libgit_include_directories,
>>
> 
>