Revert "Add additional context to protected_pip.py about how it works"

This reverts commit 84ee57d.

Author: pradyunsg

tools/protected_pip.py

@@ -1,14 +1,3 @@
-"""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
@@ -17,44 +6,32 @@
 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},
-    )
+TOX_PIP_DIR = os.path.join(VIRTUAL_ENV, "pip")
+
+
+def pip(args: List[str]) -> None:
+    # First things first, get a recent (stable) version of pip.
+    if not os.path.exists(TOX_PIP_DIR):
+        subprocess.check_call(
+            [
+                sys.executable,
+                "-m",
+                "pip",
+                "--disable-pip-version-check",
+                "install",
+                "-t",
+                TOX_PIP_DIR,
+                "pip",
+            ]
+        )
+        shutil.rmtree(glob(os.path.join(TOX_PIP_DIR, "pip-*.dist-info"))[0])
+    # And use that version.
+    pypath_env = os.environ.get("PYTHONPATH")
+    pypath = pypath_env.split(os.pathsep) if pypath_env is not None else []
+    pypath.insert(0, TOX_PIP_DIR)
+    os.environ["PYTHONPATH"] = os.pathsep.join(pypath)
+    subprocess.check_call([sys.executable, "-m", "pip"] + args)
 
 
 if __name__ == "__main__":
-    main(sys.argv[1:])
+    pip(sys.argv[1:])