Problems building Python main branch using llvm 19.1.4

[smontanaro]

Output of brew config

HOMEBREW_VERSION: 4.4.8-40-g13c3def
ORIGIN: https://github.com/Homebrew/brew
HEAD: 13c3def0496cc9af74a754187994361a8be86f0f
Last commit: 20 hours ago
Branch: master
Core tap HEAD: 50faef76469887c6cf0182e4a9ffa303a4641f19
Core tap last commit: 3 days ago
Core tap JSON: 01 Dec 20:08 UTC
Core cask tap HEAD: f9141a22df6e43f821f0931e2b60ddf860466980
Core cask tap last commit: 3 days ago
Core cask tap JSON: 01 Dec 20:08 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_BROWSER: open
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: /private/tmp/com.apple.launchd.3iNBGaC5sY/org.xquartz:0
HOMEBREW_EDITOR: /Applications/Emacs.app/Contents/MacOS/bin-arm64-11/emacsclient
HOMEBREW_MAKE_JOBS: 8
HOMEBREW_SORBET_RUNTIME: set
Homebrew Ruby: 3.3.6 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.3.6/bin/ruby
CPU: octa-core 64-bit arm_firestorm_icestorm
Clang: 16.0.0 build 1600
Git: 2.39.5 => /Applications/Xcode.app/Contents/Developer/usr/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 15.1.1-arm64
CLT: 16.1.0.0.1.1729049160
Xcode: 16.1
Rosetta 2: false

Output of brew doctor

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with debugging if you file an issue. If everything you use Homebrew for is
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Warning: Some installed formulae are deprecated or disabled.
You should find replacements for the following formulae:
  openssl@1.1
  pyside@2

Description of issue

Not sure where to report this, so assuming it's something I'm doing wrong, I'll start with the help channel. (brew ... has always just worked for me. Seeing an apparently problem with a formula is a new experience.)

Python's main branch (what will be v 3.14) requires LLVM 19 for its just-in-time compilation feature. This was working well for me until very recently (past few days), when it began failing to compile the JIT code fragments:

python3.14 ./Tools/jit/build.py aarch64-apple-darwin24.1.0

=================================================================
JIT support for aarch64-apple-darwin24.1.0 is still experimental!
             Please report any issues you encounter.             
=================================================================

In file included from /Users/skip/src/python/cpython/Tools/jit/shim.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
In file included from /private/var/folders/d6/rzq9g7qd7zn5pwbc3pj1sthc0000gn/T/tmpi6gbzqqv/_BINARY_OP.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
In file included from /private/var/folders/d6/rzq9g7qd7zn5pwbc3pj1sthc0000gn/T/tmpi6gbzqqv/_BINARY_OP_ADD_FLOAT.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
In file included from /private/var/folders/d6/rzq9g7qd7zn5pwbc3pj1sthc0000gn/T/tmpi6gbzqqv/_BINARY_OP_ADD_INT.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
In file included from /private/var/folders/d6/rzq9g7qd7zn5pwbc3pj1sthc0000gn/T/tmpi6gbzqqv/_BINARY_OP_ADD_UNICODE.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
In file included from /private/var/folders/d6/rzq9g7qd7zn5pwbc3pj1sthc0000gn/T/tmpi6gbzqqv/_BINARY_OP_INPLACE_ADD_UNICODE.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
In file included from /private/var/folders/d6/rzq9g7qd7zn5pwbc3pj1sthc0000gn/T/tmpi6gbzqqv/_BINARY_OP_MULTIPLY_INT.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
In file included from /private/var/folders/d6/rzq9g7qd7zn5pwbc3pj1sthc0000gn/T/tmpi6gbzqqv/_BINARY_OP_MULTIPLY_FLOAT.c:1:
/Users/skip/src/python/cpython/Include/Python.h:19:10: fatal error: 'assert.h' file not found
   19 | #include <assert.h>               // assert()
      |          ^~~~~~~~~~
1 error generated.
1 error generated.
1 error generated.
1 error generated.
1 error generated.
1 error generated.
1 error generated.
1 error generated.
  + Exception Group Traceback (most recent call last):
  |   File "/Users/skip/src/python/cpython/./Tools/jit/build.py", line 28, in <module>
  |     args.target.build(pathlib.Path.cwd(), comment=comment, force=args.force)
  |     ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/Users/skip/src/python/cpython/Tools/jit/_targets.py", line 196, in build
  |     stencil_groups = asyncio.run(self._build_stencils())
  |   File "/Users/skip/.local/lib/python3.14t/asyncio/runners.py", line 203, in run
  |     return runner.run(main)
  |            ~~~~~~~~~~^^^^^^
  |   File "/Users/skip/.local/lib/python3.14t/asyncio/runners.py", line 127, in run
  |     return self._loop.run_until_complete(task)
  |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  |   File "/Users/skip/.local/lib/python3.14t/asyncio/base_events.py", line 720, in run_until_complete
  |     return future.result()
  |            ~~~~~~~~~~~~~^^
  |   File "/Users/skip/src/python/cpython/Tools/jit/_targets.py", line 158, in _build_stencils
  |     async with asyncio.TaskGroup() as group:
  |                ~~~~~~~~~~~~~~~~~^^
  |   File "/Users/skip/.local/lib/python3.14t/asyncio/taskgroups.py", line 71, in __aexit__
  |     return await self._aexit(et, exc)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/Users/skip/.local/lib/python3.14t/asyncio/taskgroups.py", line 173, in _aexit
  |     raise BaseExceptionGroup(
  |     ...<2 lines>...
  |     ) from None
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "/Users/skip/src/python/cpython/Tools/jit/_targets.py", line 145, in _compile
    |     await _llvm.run("clang", args, echo=self.verbose)
    |   File "/Users/skip/src/python/cpython/Tools/jit/_llvm.py", line 97, in run
    |     output = await maybe_run(tool, args, echo=echo)
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/Users/skip/src/python/cpython/Tools/jit/_llvm.py", line 92, in maybe_run
    |     return path and await _run(path, args, echo=echo)
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/Users/skip/src/python/cpython/Tools/jit/_llvm.py", line 51, in _run
    |     raise RuntimeError(f"{tool} exited with return code {process.returncode}")
    | RuntimeError: clang exited with return code 1
    +------------------------------------
make: *** [jit_stencils.h] Error 1

I opened an issue on Python github. One of the comments indicated something went wrong between 19.1.2 and 19.1.4. (This suggests it's not something I'm doing wrong.)

Where should I report this? I noted while poking around the LLVM website that the current release appears to be 19.1.0. Is there a good reason for Homebrew to run ahead of that?

Relevant casks

llvm

[carlocab]

Try doing

mkdir -p ~/.config/clang
echo "--sysroot=$(xcrun --show-sdk-path)" >> ~/.config/clang/aarch64-apple-darwin24.1.0.cfg

and see if that helps.

[smontanaro]

Thanks! That seems to have done the trick.