Rename tox_pip.py to protected_pip.py

noxfile.py

@@ -21,7 +21,7 @@
 
 LOCATIONS = {
     "common-wheels": "tests/data/common_wheels",
-    "protected-pip": "tools/tox_pip.py",
+    "protected-pip": "tools/protected_pip.py",
 }
 REQUIREMENTS = {
     "docs": "docs/requirements.txt",

tools/protected_pip.py

@@ -0,0 +1,60 @@
+"""Maintain and use a protected copy of pip for use during development.
+
+The protected copy of pip can be used to manipulate the environment while keeping a
+potentially-non-functional installation of in-development pip in the development virtual
+environment.
+
+This allows for setting up the test environments and exercising the in-development code,
+even when it is not functional-enough to install the packages for setting up the
+environment that it is being used it.
+"""
+
+import os
+import shutil
+import subprocess
+import sys
+from glob import glob
+from typing import List
+
+VIRTUAL_ENV = os.environ["VIRTUAL_ENV"]
+PROTECTED_PIP_DIR = os.path.join(VIRTUAL_ENV, "pip")
+
+
+def _setup_protected_pip() -> None:
+    # This setup happens before any development version of pip is installed in this
+    # environment. So, at this point, the existing pip installation should be from a
+    # stable release and can be safely used to create the protected copy.
+    subprocess.check_call(
+        [
+            sys.executable,
+            "-m",
+            "pip",
+            "--disable-pip-version-check",
+            "install",
+            "-t",
+            PROTECTED_PIP_DIR,
+            "pip",
+        ]
+    )
+    # Make it impossible for pip (and other Python tooling) to discover this protected
+    # installation of pip using the metadata, by deleting the metadata.
+    shutil.rmtree(glob(os.path.join(PROTECTED_PIP_DIR, "pip-*.dist-info"))[0])
+
+
+def main(args: List[str]) -> None:
+    # If we don't have a protected pip, let's set it up.
+    if not os.path.exists(PROTECTED_PIP_DIR):
+        _setup_protected_pip()
+
+    # Run Python, with the protected pip copy on PYTHONPATH.
+    old_PYTHONPATH_entries = os.environ.get("PYTHONPATH", "").split(os.pathsep)
+    new_PYTHONPATH = os.pathsep.join([PROTECTED_PIP_DIR] + old_PYTHONPATH_entries)
+
+    subprocess.check_call(
+        [sys.executable, "-m", "pip"] + args,
+        env={"PYTHONPATH": new_PYTHONPATH},
+    )
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])