bpo-40448: ensurepip: Do not use cache (GH-19812)

ensurepip optionally installs or upgrades 'pip' and 'setuptools' using
the version of those modules bundled with Python.  The internal PIP
installation routine by default temporarily uses its cache, if it
exists.  This is undesirable as Python builds and installations may be
independent of the user running the build, whilst PIP cache location
is dependent on the user's environment and outside of the build
environment.

At the same time, there's no value in using the cache while installing
bundled modules.

This change disables PIP caching when used in ensurepip.

Lib/ensurepip/__init__.py

@@ -119,7 +119,7 @@ def _bootstrap(*, root=None, upgrade=False, user=False,
             additional_paths.append(os.path.join(tmpdir, wheel_name))
 
         # Construct the arguments to be passed to the pip command
-        args = ["install", "--no-index", "--find-links", tmpdir]
+        args = ["install", "--no-cache-dir", "--no-index", "--find-links", tmpdir]
         if root:
             args += ["--root", root]
         if upgrade:

Lib/test/test_ensurepip.py

@@ -40,7 +40,7 @@ def test_basic_bootstrapping(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "setuptools", "pip",
             ],
             unittest.mock.ANY,
@@ -54,7 +54,7 @@ def test_bootstrapping_with_root(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "--root", "/foo/bar/",
                 "setuptools", "pip",
             ],
@@ -66,7 +66,7 @@ def test_bootstrapping_with_user(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "--user", "setuptools", "pip",
             ],
             unittest.mock.ANY,
@@ -77,7 +77,7 @@ def test_bootstrapping_with_upgrade(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "--upgrade", "setuptools", "pip",
             ],
             unittest.mock.ANY,
@@ -88,7 +88,7 @@ def test_bootstrapping_with_verbosity_1(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "-v", "setuptools", "pip",
             ],
             unittest.mock.ANY,
@@ -99,7 +99,7 @@ def test_bootstrapping_with_verbosity_2(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "-vv", "setuptools", "pip",
             ],
             unittest.mock.ANY,
@@ -110,7 +110,7 @@ def test_bootstrapping_with_verbosity_3(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "-vvv", "setuptools", "pip",
             ],
             unittest.mock.ANY,
@@ -260,7 +260,7 @@ def test_basic_bootstrapping(self):
 
         self.run_pip.assert_called_once_with(
             [
-                "install", "--no-index", "--find-links",
+                "install", "--no-cache-dir", "--no-index", "--find-links",
                 unittest.mock.ANY, "setuptools", "pip",
             ],
             unittest.mock.ANY,

Misc/ACKS

@@ -910,6 +910,7 @@ Vajrasky Kok
 Guido Kollerie
 Jacek Kołodziej
 Jacek Konieczny
+Krzysztof Konopko
 Arkady Koplyarov
 Peter A. Koren
 Марк Коренберг

Misc/NEWS.d/next/Library/2020-06-15-12-22-53.bpo-40448.1dk8Bu.rst

@@ -0,0 +1,2 @@
+:mod:`ensurepip` now disables the use of `pip` cache when installing the
+bundled versions of `pip` and `setuptools`.  Patch by Krzysztof Konopko.