Avoid redundant installation of pip and setuptools

server/pypi/build-wheel.py

@@ -66,7 +66,6 @@ class Abi:
 
 
 class BuildWheel:
-
     def main(self):
         try:
             self.parse_args()
@@ -126,8 +125,7 @@ def unpack_and_build(self):
             assert_isdir(self.build_dir)
         else:
             ensure_empty(self.build_dir)
-            run(f"python{self.python} -m venv {build_env_dir}")
-            run(f"{self.pip} install -r {PYPI_DIR}/requirements-build-env.txt")
+            run(f"python{self.python} {PYPI_DIR}/create-build-env.py {build_env_dir}")
             self.unpack_source()
             self.apply_patches()
 

server/pypi/create-build-env.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+
+import argparse
+import ensurepip
+from glob import glob
+import os
+from os.path import abspath, dirname, exists
+from shlex import split
+import subprocess
+import venv
+
+
+PYPI_DIR = abspath(dirname(__file__))
+
+ap = argparse.ArgumentParser()
+ap.add_argument("build_env_dir")
+args = ap.parse_args()
+
+# Installing Python's bundled pip and setuptools into the environment is pointless since
+# we're just going to replace them anyway. Instead, use the bundled pip to install our
+# requirements file directly. This saves about 3.5 seconds on Python 3.8, and 6 seconds
+# on Python 3.11.
+assert not exists(args.build_env_dir)
+venv.create(args.build_env_dir, with_pip=False)
+
+pip_whl, = glob(f"{ensurepip.__path__[0]}/_bundled/pip-*.whl")  # Note comma
+env = os.environ.copy()
+env["PYTHONPATH"] = pip_whl
+
+subprocess.run(
+    split(f"{args.build_env_dir}/bin/python -m") +
+    split(f"pip install -r {PYPI_DIR}/requirements-build-env.txt"),
+    env=env, check=True)