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 @@ class TestBootstrap(EnsurepipMixin, unittest.TestCase):
 
         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 @@ class TestBootstrap(EnsurepipMixin, unittest.TestCase):
 
         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 @@ class TestBootstrap(EnsurepipMixin, unittest.TestCase):
 
         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 @@ class TestBootstrap(EnsurepipMixin, unittest.TestCase):
 
         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 @@ class TestBootstrap(EnsurepipMixin, unittest.TestCase):
 
         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 @@ class TestBootstrap(EnsurepipMixin, unittest.TestCase):
 
         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 @@ class TestBootstrap(EnsurepipMixin, unittest.TestCase):
 
         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 @@ class TestBootstrappingMainFunction(EnsurepipMixin, unittest.TestCase):
 
         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.