Add 'tempfile_compat' to handle windows tmp files

`pip` is not aware that it's reading from a tempfile. On Windows, this is
significant, and we can't guarantee good behavior except by setting
`delete=False` on the tempfile object. That done, we become responsible
for the cleanup as well, which is just a final pair of close()+unlink()
calls.

Author: sirosen

piptools/_compat/tempfile_compat.py

@@ -0,0 +1,28 @@
+"""
+Compatibility helpers for :mod:`tempfile` usage across platforms
+and python versions.
+"""
+
+from __future__ import annotations
+
+import contextlib
+import os
+import tempfile
+import typing as _t
+from collections.abc import Iterator
+
+
+@contextlib.contextmanager
+def named_temp_file(mode: str = "wt") -> Iterator[_t.IO[str]]:
+    """
+    A safe wrapper over NamedTemporaryFile for usage on Windows as well as
+    POSIX systems.
+
+    The issue we have is that we cannot guarantee that ``pip`` will open temporary
+    files on Windows with ``O_TEMPORARY`` when passed the path, resulting in surprising
+    behavior.
+    """
+    temp_file = tempfile.NamedTemporaryFile(mode=mode, delete=False)
+    yield temp_file
+    temp_file.close()
+    os.unlink(temp_file.name)

piptools/scripts/compile.py

@@ -4,7 +4,6 @@
 import os
 import shlex
 import sys
-import tempfile
 import typing as _t
 from pathlib import Path
 
@@ -14,7 +13,7 @@
 from pip._internal.req import InstallRequirement
 from pip._internal.utils.misc import redact_auth_from_url
 
-from .._compat import canonicalize_name, parse_requirements
+from .._compat import canonicalize_name, parse_requirements, tempfile_compat
 from .._internal import _pip_api
 from ..build import ProjectMetadata, build_project_metadata
 from ..cache import DependencyCache
@@ -355,7 +354,7 @@ def cli(
             # pip requires filenames and not files. Since we want to support
             # piping from stdin, we need to briefly save the input from stdin
             # to a temporary file and have pip read that.
-            with tempfile.NamedTemporaryFile(mode="wt") as tmpfile:
+            with tempfile_compat.named_temp_file() as tmpfile:
                 tmpfile.write(sys.stdin.read())
                 tmpfile.flush()
                 reqs = list(
@@ -414,7 +413,7 @@ def cli(
         )
 
     if upgrade_packages:
-        with tempfile.NamedTemporaryFile(mode="wt") as constraints_file:
+        with tempfile_compat.named_temp_file() as constraints_file:
             constraints_file.write("\n".join(upgrade_packages))
             constraints_file.flush()
             reqs = list(

tests/test_cli_compile.py

@@ -9,7 +9,6 @@
 import shutil
 import subprocess
 import sys
-import tempfile
 import typing as _t
 from textwrap import dedent
 from unittest import mock
@@ -22,6 +21,7 @@
 from pip._internal.utils.urls import path_to_url
 from pip._vendor.packaging.version import Version
 
+from piptools._compat import tempfile_compat
 from piptools._internal import _pip_api
 from piptools.build import ProjectMetadata
 from piptools.scripts.compile import cli
@@ -1487,32 +1487,33 @@ def test_tmpfile_for_stdin_is_cleaned_up(pip_conf, runner):
     tmpfile_name = None
 
     # save the real constructor so that it can be used while `mock.patch()` is
-    # active -- also, it's a function, not a class, so we can't inherit from it
-    real_constructor = tempfile.NamedTemporaryFile
+    # active
+    real_constructor = tempfile_compat.named_temp_file
 
-    # a "spy" which can be mocked into place for `NamedTemporaryFile` to
+    # a "spy" which can be mocked into place for `named_temp_file` to
     # replace the implementation with one which has side-effects and makes test
     # assertions
     #
     # this spy ensures that the file is deleted on exit
-    # it also sets a nonlocal to indicate that it was initialized at all
     class NamedTempfileSpy:
         def __init__(self, *args, **kwargs):
-            self._tmpfile = real_constructor(*args, **kwargs)
+            self._ctx_manager = real_constructor(*args, **kwargs)
 
         def __enter__(self):
-            ret = self._tmpfile.__enter__()
+            ret = self._ctx_manager.__enter__()
             nonlocal tmpfile_name
-            tmpfile_name = self._tmpfile.name
+            tmpfile_name = ret.name
             return ret
 
         def __exit__(self, *args, **kwargs):
-            assert os.path.exists(self._tmpfile.name)
-            ret = self._tmpfile.__exit__(*args, **kwargs)
-            assert not os.path.exists(self._tmpfile.name)
+            assert os.path.exists(tmpfile_name)
+            ret = self._ctx_manager.__exit__(*args, **kwargs)
+            assert not os.path.exists(tmpfile_name)
             return ret
 
-    with mock.patch("tempfile.NamedTemporaryFile", NamedTempfileSpy):
+    with mock.patch(
+        "piptools._compat.tempfile_compat.named_temp_file", NamedTempfileSpy
+    ):
         out = runner.invoke(
             cli,
             ["-", "--output-file", "-", "--quiet", "--no-emit-options", "--no-header"],