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diff -up pip-19.3.1/news/7872.bugfix.pip7873 pip-19.3.1/news/7872.bugfix
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--- pip-19.3.1/news/7872.bugfix.pip7873	2022-05-24 08:34:03.285054864 -0600
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+++ pip-19.3.1/news/7872.bugfix	2022-05-24 08:34:03.285054864 -0600
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@@ -0,0 +1 @@
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+Prevent an infinite recursion with ``pip wheel`` when ``$TMPDIR`` is within the source directory.
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diff -up pip-19.3.1/src/pip/_internal/download.py.pip7873 pip-19.3.1/src/pip/_internal/download.py
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--- pip-19.3.1/src/pip/_internal/download.py.pip7873	2019-10-17 13:32:34.000000000 -0600
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+++ pip-19.3.1/src/pip/_internal/download.py	2022-05-24 08:35:17.013833331 -0600
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@@ -350,12 +350,24 @@ def _copy2_ignoring_special_files(src, d
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 def _copy_source_tree(source, target):
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     # type: (str, str) -> None
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+    target_abspath = os.path.abspath(target)
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+    target_basename = os.path.basename(target_abspath)
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+    target_dirname = os.path.dirname(target_abspath)
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+
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     def ignore(d, names):
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-        # Pulling in those directories can potentially be very slow,
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-        # exclude the following directories if they appear in the top
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-        # level dir (and only it).
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-        # See discussion at https://github.com/pypa/pip/pull/6770
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-        return ['.tox', '.nox'] if d == source else []
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+        skipped = []  # type: List[str]
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+        if d == source:
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+            # Pulling in those directories can potentially be very slow,
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+            # exclude the following directories if they appear in the top
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+            # level dir (and only it).
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+            # See discussion at https://github.com/pypa/pip/pull/6770
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+            skipped += ['.tox', '.nox']
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+        if os.path.abspath(d) == target_dirname:
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+            # Prevent an infinite recursion if the target is in source.
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+            # This can happen when TMPDIR is set to ${PWD}/...
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+            # and we copy PWD to TMPDIR.
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+            skipped += [target_basename]
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+        return skipped
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     kwargs = dict(ignore=ignore, symlinks=True)  # type: CopytreeKwargs
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diff -up pip-19.3.1/src/pip/_internal/operations/prepare.py.pip7873 pip-19.3.1/src/pip/_internal/operations/prepare.py
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diff -up pip-19.3.1/tests/data/src/extension/extension.c.pip7873 pip-19.3.1/tests/data/src/extension/extension.c
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diff -up pip-19.3.1/tests/data/src/extension/setup.py.pip7873 pip-19.3.1/tests/data/src/extension/setup.py
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--- pip-19.3.1/tests/data/src/extension/setup.py.pip7873	2022-05-24 08:34:03.285054864 -0600
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+++ pip-19.3.1/tests/data/src/extension/setup.py	2022-05-24 08:34:03.285054864 -0600
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@@ -0,0 +1,4 @@
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+from setuptools import Extension, setup
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+
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+module = Extension('extension', sources=['extension.c'])
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+setup(name='extension', version='0.0.1', ext_modules = [module])
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diff -up pip-19.3.1/tests/functional/test_wheel.py.pip7873 pip-19.3.1/tests/functional/test_wheel.py
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--- pip-19.3.1/tests/functional/test_wheel.py.pip7873	2019-10-17 13:32:34.000000000 -0600
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+++ pip-19.3.1/tests/functional/test_wheel.py	2022-05-24 08:34:03.285054864 -0600
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@@ -1,6 +1,7 @@
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 """'pip wheel' tests"""
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 import os
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 import re
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+import sys
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 from os.path import exists
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 import pytest
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@@ -228,6 +229,24 @@ def test_pip_wheel_with_user_set_in_conf
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     assert "Successfully built withpyproject" in result.stdout, result.stdout
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+@pytest.mark.skipif(sys.platform.startswith('win'),
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+                    reason='The empty extension module does not work on Win')
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+def test_pip_wheel_ext_module_with_tmpdir_inside(script, data, common_wheels):
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+    tmpdir = data.src / 'extension/tmp'
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+    tmpdir.mkdir()
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+    script.environ['TMPDIR'] = str(tmpdir)
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+
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+    # To avoid a test dependency on a C compiler, we set the env vars to "noop"
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+    # The .c source is empty anyway
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+    script.environ['CC'] = script.environ['LDSHARED'] = str('true')
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+
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+    result = script.pip(
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+        'wheel', data.src / 'extension',
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+        '--no-index', '-f', common_wheels
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+    )
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+    assert "Successfully built extension" in result.stdout, result.stdout
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+
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+
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 @pytest.mark.network
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 def test_pep517_wheels_are_not_confused_with_other_files(script, tmpdir, data):
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     """Check correct wheels are copied. (#6196)