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In [pypa/setuptools#2228](https://github.com/pypa/setuptools/issues/2228), by adopting the distutils codebase from a late release of CPython, Setuptools stumbled onto an API-breaking change in distutils rooted at issue39763.
Details are in the Setuptools investigation, but to summarize:
- distutils.ccompiler.CCompiler.compile declares "raises CompileError on failure" and calls `self._compile`, implemented by subclasses.
- In at least `distutils.unixcompiler.UnixCCompiler._compile`, `distutils.spawn.spawn` is called (through CCompiler.spawn).
- Since GH-18743, `distutils.spawn.spawn` calls `subprocess.Popen` which raises FileNotFoundError when the target executable doesn't exist.
- Programs trapping CompileError but not FileNotFoundError will crash where once they had error handling.
Setuptools discovered this behavior in the 48.0 release when it incorporated these distutils changes into a vendored release of Setuptools, but the failures exhibited will apply to all builds (including pyyaml) on Python 3.9.