Re: [PATCH] regex: not all macOS platforms seem to have REG_ENHANCED

From: René Scharfe <l.s.r@web.de>
Date: Mar 20, 2026, 11:12 UTC
Message-ID: <5b8e24c2-452c-486e-a143-386e06a75e03@web.de>
In-Reply-To: <d340af9e-334c-4e81-e58a-fc3dea73ebdd@gmx.de>

On 3/20/26 9:55 AM, Johannes Schindelin wrote:

Show 72 quoted lines

> Me again, sorry,
> 
> On Fri, 20 Mar 2026, Johannes Schindelin wrote:
> 
>> On Fri, 20 Mar 2026, Johannes Schindelin wrote:
>>
>>> On Fri, 20 Mar 2026, Junio C Hamano wrote:
>>>
>>>> The build seems to have started failing on macos-14 CI jobs at
>>>> GitHub, however, as apparently not all the macOS platforms have this
>>>> flag defined.
>>
>> [... I need to ...] recommend something like this in the `Darwin` clause
>> in `config.mak.uname`:
>>
>> -- snipsnap --
>> diff --git a/config.mak.uname b/config.mak.uname
>> index f9ffefa67a4f..572f8967bc36 100644
>> --- a/config.mak.uname
>> +++ b/config.mak.uname
>> @@ -172,6 +172,10 @@ ifeq ($(uname_S),Darwin)
>>  		NEEDS_GOOD_LIBICONV = UnfortunatelyYes
>>          endif
>>  
>> +	ifeq ($(CC),clang)
>> +		NO_REGEX = HomebrewsClangSeemsToBeMissingEnhancedRegexSupportAsOfMarch2026
>> +	endif
>> +
>>  	# The builtin FSMonitor on MacOS builds upon Simple-IPC.  Both require
>>  	# Unix domain sockets and PThreads.
>>          ifndef NO_PTHREADS
> 
> Turns out that my analysis was not _quite_ complete yet. With Claude Opus'
> assistance, I was able to find the exact turn of events that led to the CI
> failure. Here is my proposal for an alternative to your patch, Junio (the
> https://github.com/git-for-windows/git/actions/runs/23335584918 shows that
> the build completed successfully this time; the tests are still running as
> of time of writing, of course):
> 
> -- snipsnap --
> From f65b3b657c36e9132624ea223c90047527edea59 Mon Sep 17 00:00:00 2001
> From: Johannes Schindelin <johannes.schindelin@gmx.de>
> Date: Fri, 20 Mar 2026 09:09:10 +0100
> Subject: [PATCH] osx-clang: work around Homebrew's clang lacking REG_ENHANCED
> 
> The `osx-clang` and `osx-reftable` CI jobs on macOS started failing
> with:
> 
>     compat/regcomp_enhanced.c:7:13: error: use of undeclared identifier
>     'REG_ENHANCED'
> 
> The failure coincides with the GitHub Actions `macos-14-arm64` runner
> image being updated from `20260302.0147` to `20260317.0174`.  The key
> change in that image update is the Homebrew version bump from 5.0.15 to
> 5.1.0.
> 
> Homebrew 5.1.0 introduced automatic linking for versioned keg-only
> formulae when the unversioned sibling is absent (see
> https://github.com/Homebrew/brew/pull/21676, announced at
> https://brew.sh/2026/03/10/homebrew-5.1.0/).  The runner image installs
> `llvm@15` (keg-only) but not unversioned `llvm`.  Under Homebrew 5.0.x
> that formula stayed in its keg and its `clang` binary only lived at
> `$(brew --prefix llvm@15)/bin/clang`.  Under 5.1.0, because unversioned
> `llvm` is absent, `llvm@15` is now auto-linked into
> `/opt/homebrew/bin/`, which sits earlier in PATH than `/usr/bin`.
> 
> The net effect is that `CC=clang` in CI now silently resolves to
> Homebrew's LLVM 15.0.7 clang instead of Apple's system clang (Apple
> clang 15.0.0, bundled with Xcode 15.4).  The runner image README
> confirms this: the reported "Clang/LLVM" version flipped from 15.0.0 to
> 15.0.7 between image releases, matching the Homebrew LLVM version
> exactly.

Good find!

Show 7 quoted lines

> Homebrew's LLVM clang uses different include paths from Apple's clang.
> In particular, the `regex.h` it sees does not define `REG_ENHANCED`,
> which is an Apple-specific extension present in the macOS SDK headers
> since at least macOS 10.12.  The Makefile unconditionally sets
> `USE_ENHANCED_BASIC_REGULAR_EXPRESSIONS` for all Darwin builds via
> `config.mak.uname`, which pulls in `compat/regcomp_enhanced.c`, which
> references `REG_ENHANCED`, hence the build failure.

I suspect it uses the same regex.h. The definition of REG_ENHANCED is gated by a __MAC_OS_X_VERSION_MIN_REQUIRED check, though, and that fails because __MAC_OS_X_VERSION_MIN_REQUIRED is defined as __ENVIRONMENT_OS_VERSION_MIN_REQUIRED__ and that one in turn is not defined by the Homebrew version of clang in the runner.

I can't reproduce this locally, by the way. /opt/homebrew/Cellar/llvm/22.1.1/bin/clang is not linked to /opt/homebrew/bin on my machine and also provides a sensible definition of __MAC_OS_X_VERSION_MIN_REQUIRED.

Show 10 quoted lines

> The `osx-gcc` job (CC=gcc-13) is unaffected because Homebrew GCC is
> configured to use Apple's SDK sysroot, so it still picks up Apple's
> `regex.h` which defines `REG_ENHANCED`.  The `osx-meson` job is
> unaffected because Meson does a compile-time test for `REG_ENHANCED`
> (via `compiler.get_define`) and simply skips the feature when it is
> absent.
> 
> Work around this by setting `NO_REGEX` when `CC=clang` on Darwin, which
> makes the build use Git's bundled regex implementation instead of the
> system one.  This sidesteps the missing `REG_ENHANCED` define entirely.

Or how about using /usr/bin/clang explicitly on macOS instead of any old clang from $PATH? That would avoid user-visible changes.

Show 27 quoted lines

> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  config.mak.uname | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/config.mak.uname b/config.mak.uname
> index e6efd0f30913..c437accbcc50 100644
> --- a/config.mak.uname
> +++ b/config.mak.uname
> @@ -162,6 +162,17 @@ ifeq ($(uname_S),Darwin)
>  		NEEDS_GOOD_LIBICONV = UnfortunatelyYes
>          endif
>  
> +	# Homebrew's LLVM clang ships a regex.h that lacks REG_ENHANCED,
> +	# which is needed for USE_ENHANCED_BASIC_REGULAR_EXPRESSIONS above.
> +	# Use our bundled regex instead.  This became a practical problem
> +	# when Homebrew 5.1.0 started auto-linking versioned keg-only
> +	# formulae (like llvm@15) into $(HOMEBREW_PREFIX)/bin/, causing
> +	# CC=clang in CI to silently pick up Homebrew's clang instead of
> +	# Apple's /usr/bin/clang.
> +	ifeq ($(CC),clang)
> +		NO_REGEX = HomebrewsClangUsesARegexThatLacksREG_ENHANCED
> +	endif
> +
>  	# The builtin FSMonitor on MacOS builds upon Simple-IPC.  Both require
>  	# Unix domain sockets and PThreads.
>          ifndef NO_PTHREADS