Add global TempDirectory manager

In cases where there is not a clear scope, or where enforcing a scope
and passing a temp directory to callees creates unnecessary coupling
between components, this will let us tie the lifetime of temporary
directories to the lifetime of the application without using e.g.
atexit or finalizers.

This has the benefit of being easier to test and reason about.

src/pip/_internal/utils/temp_dir.py

@@ -8,17 +8,35 @@ import itertools
 import logging
 import os.path
 import tempfile
+from contextlib import contextmanager
+
+from pip._vendor.contextlib2 import ExitStack
 
 from pip._internal.utils.misc import rmtree
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
 
 if MYPY_CHECK_RUNNING:
-    from typing import Optional
+    from typing import Iterator, Optional
 
 
 logger = logging.getLogger(__name__)
 
 
+_tempdir_manager = None  # type: Optional[ExitStack]
+
+
+@contextmanager
+def global_tempdir_manager():
+    # type: () -> Iterator[None]
+    global _tempdir_manager
+    with ExitStack() as stack:
+        old_tempdir_manager, _tempdir_manager = _tempdir_manager, stack
+        try:
+            yield
+        finally:
+            _tempdir_manager = old_tempdir_manager
+
+
 class TempDirectory(object):
     """Helper class that owns and cleans up a temporary directory.
 
@@ -44,7 +62,8 @@ class TempDirectory(object):
         self,
         path=None,    # type: Optional[str]
         delete=None,  # type: Optional[bool]
-        kind="temp"
+        kind="temp",  # type: str
+        globally_managed=False,  # type: bool
     ):
         super(TempDirectory, self).__init__()
 
@@ -61,6 +80,10 @@ class TempDirectory(object):
         self.delete = delete
         self.kind = kind
 
+        if globally_managed:
+            assert _tempdir_manager is not None
+            _tempdir_manager.enter_context(self)
+
     @property
     def path(self):
         # type: () -> str

tests/unit/test_utils_temp_dir.py

@@ -5,8 +5,13 @@ import tempfile
 
 import pytest
 
+from pip._internal.utils import temp_dir
 from pip._internal.utils.misc import ensure_dir
-from pip._internal.utils.temp_dir import AdjacentTempDirectory, TempDirectory
+from pip._internal.utils.temp_dir import (
+    AdjacentTempDirectory,
+    TempDirectory,
+    global_tempdir_manager,
+)
 
 
 # No need to test symlinked directories on Windows
@@ -188,3 +193,17 @@ def test_adjacent_directory_permission_error(monkeypatch):
         with pytest.raises(OSError):
             with AdjacentTempDirectory(original):
                 pass
+
+
+def test_global_tempdir_manager():
+    with global_tempdir_manager():
+        d = TempDirectory(globally_managed=True)
+        path = d.path
+        assert os.path.exists(path)
+    assert not os.path.exists(path)
+
+
+def test_tempdirectory_asserts_global_tempdir(monkeypatch):
+    monkeypatch.setattr(temp_dir, "_tempdir_manager", None)
+    with pytest.raises(AssertionError):
+        TempDirectory(globally_managed=True)