Factor out build script

also, set SOURCE_DATE_EPOCH, and use python -I

Author: sbidoul

.github/workflows/release.yml

@@ -13,10 +13,7 @@ jobs:
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
       - name: Build a binary wheel and a source tarball
-        run: |
-          python3 -m venv build-env
-          build-env/bin/python -m pip install --no-deps --only-binary :all: --require-hashes -r build-requirements.txt
-          build-env/bin/python -m build --no-isolation
+        run: ./build-project.py
       - name: Store the distribution packages
         uses: actions/upload-artifact@65c4c4a1ddee5b72f698fdd19549f0f0fb45cf08 # v4
         with:

MANIFEST.in

@@ -7,6 +7,7 @@ include pyproject.toml
 
 include build-requirements.in
 include build-requirements.txt
+include build-project.py
 
 include src/pip/_vendor/README.rst
 include src/pip/_vendor/vendor.txt

build-project.py

@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+"""Build pip using pinned build requirements."""
+
+import subprocess
+import sys
+import tempfile
+from pathlib import Path
+
+
+def get_git_head_timestamp() -> str:
+    return subprocess.run(
+        [
+            "git",
+            "log",
+            "-1",
+            "--pretty=format:%ct",
+        ],
+        text=True,
+        stdout=subprocess.PIPE,
+    ).stdout.strip()
+
+
+def main() -> None:
+    with tempfile.TemporaryDirectory() as build_env:
+        subprocess.run(
+            [
+                sys.executable,
+                "-m",
+                "venv",
+                build_env,
+            ],
+            check=True,
+        )
+        build_python = Path(build_env) / "bin" / "python"
+        subprocess.run(
+            [
+                build_python,
+                "-Im",
+                "pip",
+                "install",
+                "--no-deps",
+                "--only-binary=:all:",
+                "--require-hashes",
+                "-r",
+                Path(__file__).parent / "build-requirements.txt",
+            ],
+            check=True,
+        )
+        subprocess.run(
+            [
+                build_python,
+                "-Im",
+                "build",
+                "--no-isolation",
+            ],
+            check=True,
+            env={"SOURCE_DATE_EPOCH": get_git_head_timestamp()},
+        )
+
+
+if __name__ == "__main__":
+    main()