Meson fails to build NumPy on Python 3.15.0af with `AttributeError: 'NoneType' object has no attribute 'split'`

[Nevsor]

Describe the bug
Meson fails to build NumPy on Python 3.15.0af with AttributeError: 'NoneType' object has no attribute 'split'

The error message contains UnicodeDecodeErrors that might be related to Python 3.15 changing the default encoding from "locale" to "utf8" https://docs.python.org/3.15/whatsnew/3.15.html#whatsnew315-utf8-default

To Reproduce

This works: py -3.14 -m pip install numpy==2.3.5
This doesn't: py -3.15.0a3 -m pip install numpy==2.3.5
This works (Powershell): $env:PYTHONUTF8=0; py -3.15.0a3 -m pip install numpy==2.3.5

Expected behavior
Meson builds NumPy without errors.

system parameters

• Build using pip
• Windows 11
• Python 3.15.0a3
• pip 25.3
• Meson 1.8.3

Error message:

$py -3.15.0a3 -m pip install numpy
Collecting numpy
  Using cached numpy-2.3.5.tar.gz (20.6 MB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
  Installing backend dependencies ... done
  Preparing metadata (pyproject.toml) ... error
  error: subprocess-exited-with-error

  × Preparing metadata (pyproject.toml) did not run successfully.
  │ exit code: 2
  ╰─> [89 lines of output]
      + C:\Users\stes\AppData\Local\Python\pythoncore-3.15-64\python.exe C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\meson.py setup C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204 C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\.mesonpy-bona1k7k -Dbuildtype=release -Db_ndebug=if-release -Db_vscrt=md --native-file=C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\.mesonpy-bona1k7k\meson-python-native-file.ini
      Exception in thread Thread-3 (_readerthread):
      Exception in thread Thread-4 (_readerthread):
      Traceback (most recent call last):
        File "C:\Users\stes\AppData\Local\Python\pythoncore-3.15-64\Lib\threading.py", line 1075, in _bootstrap_inner
          self._context.run(self.run)
          ~~~~~~~~~~~~~~~~~^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Python\pythoncore-3.15-64\Lib\threading.py", line 1017, in run
          self._target(*self._args, **self._kwargs)
          ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Python\pythoncore-3.15-64\Lib\subprocess.py", line 1612, in _readerthread
          buffer.append(fh.read())
                        ~~~~~~~^^
      Traceback (most recent call last):
        File "<frozen codecs>", line 325, in decode
        File "C:\Users\stes\AppData\Local\Python\pythoncore-3.15-64\Lib\threading.py", line 1075, in _bootstrap_inner
          self._context.run(self.run)
          ~~~~~~~~~~~~~~~~~^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Python\pythoncore-3.15-64\Lib\threading.py", line 1017, in run
          self._target(*self._args, **self._kwargs)
          ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Python\pythoncore-3.15-64\Lib\subprocess.py", line 1612, in _readerthread
          buffer.append(fh.read())
                        ~~~~~~~^^
        File "<frozen codecs>", line 325, in decode
      UnicodeDecodeError: 'utf-8' codec can't decode byte 0x81 in position 62: invalid start byte
      UnicodeDecodeError: 'utf-8' codec can't decode byte 0x84 in position 546: invalid start byte
      Traceback (most recent call last):
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\mesonmain.py", line 193, in run
          return options.run_func(options)
                 ~~~~~~~~~~~~~~~~^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\msetup.py", line 390, in run
          app.generate()
          ~~~~~~~~~~~~^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\msetup.py", line 192, in generate
          return self._generate(env, capture, vslite_ctx)
                 ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\msetup.py", line 232, in _generate
          intr = interpreter.Interpreter(b, user_defined_options=user_defined_options)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreter\interpreter.py", line 308, in __init__
          self.parse_project()
          ~~~~~~~~~~~~~~~~~~^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreterbase\interpreterbase.py", line 138, in parse_project
          self.evaluate_codeblock(self.ast, end=1)
          ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreterbase\interpreterbase.py", line 203, in evaluate_codeblock
          raise e
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreterbase\interpreterbase.py", line 195, in evaluate_codeblock
          self.evaluate_statement(cur)
          ~~~~~~~~~~~~~~~~~~~~~~~^^^^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreterbase\interpreterbase.py", line 209, in evaluate_statement
          return self.function_call(cur)
                 ~~~~~~~~~~~~~~~~~~^^^^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreterbase\interpreterbase.py", line 536, in function_call
          res = func(node, func_args, kwargs)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreterbase\decorators.py", line 237, in wrapper
          return f(*nargs, **wrapped_kwargs)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreterbase\decorators.py", line 556, in wrapper
          return f(*wrapped_args, **wrapped_kwargs)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreter\interpreter.py", line 1293, in func_project
          self.add_languages(proj_langs, True, MachineChoice.HOST)
          ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreter\interpreter.py", line 1477, in add_languages
          success = self.add_languages_for(args, required, for_machine)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\interpreter\interpreter.py", line 1520, in add_languages_for
          comp = compilers.detect_compiler_for(self.environment, lang, for_machine, skip_sanity_check, self.subproject)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\compilers\detect.py", line 106, in detect_compiler_for
          comp = compiler_from_language(env, lang, for_machine)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\compilers\detect.py", line 103, in compiler_from_language
          return lang_map[lang](env, for_machine) if lang in lang_map else None
                 ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\compilers\detect.py", line 633, in detect_c_compiler
          return _detect_c_or_cpp_compiler(env, 'c', for_machine)
        File "C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\vendored-meson\meson\mesonbuild\compilers\detect.py", line 335, in _detect_c_or_cpp_compiler
          full_version = out.split('\n', 1)[0]
                         ^^^^^^^^^
      AttributeError: 'NoneType' object has no attribute 'split'
      The Meson build system
      Version: 1.8.3
      Source dir: C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204
      Build dir: C:\Users\stes\AppData\Local\Temp\pip-install-5rkwpi51\numpy_f48b46f8cbf84c329989890b4d232204\.mesonpy-bona1k7k
      Build type: native build
      Activating VS 17.14.23
      Project name: NumPy
      Project version: 2.3.5

      ..\meson.build:1:0: ERROR: Unhandled python exception

          This is a Meson bug and should be reported!
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> numpy

note: This is an issue with the package mentioned above, not pip.
hint: See above for details.