fix: reset the cached compiler when build_ext is reinitialized

[DivyamTalwar]

Fixes #126

The problem

httptools_build_ext.initialize_options() short-circuits after the first pass, on purpose:

def initialize_options(self):
    # initialize_options() may be called multiple times on the
    # same command object, so make sure not to override previously
    # set options.
    if getattr(self, '_initialized', False):
        return
    super().initialize_options()

That early return is load-bearing — it protects the Cython settings and extension mutations applied the first time through. But setuptools calls reinitialize_command('build_ext') between phases, and the base initialize_options() it is bypassing is what clears self.compiler. So a chained invocation reaches the second phase still holding the compiler instance the first phase configured:

python setup.py build bdist_wheel

The wheel phase then runs against a stale compiler rather than selecting one for the phase it is actually in, and the build fails. Anything that drives both phases through one command — which is the normal shape for a build backend — hits it.

The fix

Clear only the transient attribute, inside the early-return path:

if getattr(self, '_initialized', False):
    self.compiler = None
    return

The obvious alternative — dropping the early return and calling the base initializer — was rejected: it discards exactly the cached command options and extension state the early return exists to protect. compiler is the one piece of per-phase state that must not survive reinitialization, so the reset is scoped to it and nothing else.

Test

tests/test_build.py is new. It loads the real setup.py via runpy (with setuptools.setup mocked out) to get the actual build_ext subclass rather than a reimplementation of it, finalizes the command, attaches a compiler, reinitializes, and asserts the run proceeds to build_extensions().

It fails on master and passes with this change.

Verification

check	result
focused regression	1 passed
python setup.py build bdist_wheel	succeeds
make test	42 passed
make typecheck	0 errors, 0 warnings
git diff --check	clean

Not covered locally: other Python versions and non-macOS platforms — left to CI.