setup.py: avoid generating cython modules during sdist build

Since the build process now always generates new C modules instead of
using bundled versions, skip creating them during the sdist process.

MANIFEST.in

@@ -1,8 +1,6 @@
 # all vcs-tracked files are auto-included by setuptools_scm
 # include bundled test data
 recursive-include testdata *
-# exclude cython-generated files
-recursive-exclude src/pkgcraft *.c
 # drop git-related files
 global-exclude .git*
 prune .github

setup.py

@@ -92,32 +92,37 @@ def initialize_options(self):
     def finalize_options(self):
         self.cython_coverage = bool(self.cython_coverage)
 
-        ext_modules = self.distribution.ext_modules[:]
+        # default to parallelizing build across all cores
+        if self.parallel is None:
+            self.parallel = cpu_count()
+
+        super().finalize_options()
+
+    def run(self):
         # default cython compiler directives
         compiler_directives = {"language_level": 3}
 
         # optionally enable coverage support for cython modules
         if self.cython_coverage:
             compiler_directives["linetrace"] = True
             trace_macros = [("CYTHON_TRACE", "1"), ("CYTHON_TRACE_NOGIL", "1")]
-            for ext in ext_modules:
+            for ext in self.extensions:
                 ext.define_macros.extend(trace_macros)
 
-        # generate C modules
-        self.distribution.ext_modules[:] = cythonize(
-            ext_modules,
+        # generate C modules with cython
+        self.extensions[:] = cythonize(
+            self.extensions,
             force=True,
             compiler_directives=compiler_directives,
             annotate=False,
         )
 
-        # default to parallelizing build across all cores
-        if self.parallel is None:
-            self.parallel = cpu_count()
+        # HACK: Force setuptools to reinject its private attributes to
+        # extension objects that were overridden by `cythonize`, otherwise the
+        # build fails when it tries to access them.
+        build_ext = self.reinitialize_command("build_ext")
+        build_ext.ensure_finalized()
 
-        super().finalize_options()
-
-    def run(self):
         # delay pkg-config to avoid requiring library during sdist
         pkgcraft_opts = pkg_config("pkgcraft")