From bd9bcef8b3262c513a0dd614731cfe8db8d64125 Mon Sep 17 00:00:00 2001
From: Tzu-ping Chung <uranusjr@gmail.com>
Date: Tue, 19 Apr 2022 17:08:57 +0800
Subject: [PATCH] Enable importlib.metadata backend on Python 3.11

---
 .github/workflows/ci.yml               |  4 ++--
 news/11044.process.rst                 |  4 ++++
 src/pip/_internal/metadata/__init__.py | 29 +++++++++++++++++++++++++-
 3 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 news/11044.process.rst

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f0b8ba644..e467b3e50 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -219,11 +219,12 @@ jobs:
         env:
           TEMP: "R:\\Temp"
 
+  # TODO: Remove this when we add Python 3.11 to CI.
   tests-importlib-metadata:
     name: tests for importlib.metadata backend
     runs-on: ubuntu-latest
     env:
-      _PIP_METADATA_BACKEND_IMPORTLIB: egg-compat
+      _PIP_USE_IMPORTLIB_METADATA: 'true'
 
     needs: [pre-commit, packaging, determine-changes]
     if: >-
@@ -241,7 +242,6 @@ jobs:
 
       - run: pip install nox 'virtualenv<20'
 
-      # Main check
       - name: Run unit tests
         run: >-
           nox -s test-3.10 --
diff --git a/news/11044.process.rst b/news/11044.process.rst
new file mode 100644
index 000000000..d33fc74d8
--- /dev/null
+++ b/news/11044.process.rst
@@ -0,0 +1,4 @@
+Enable the ``importlib.metadata`` metadata implementation by default on
+Python 3.11 (or later). The environment variable ``_PIP_USE_IMPORTLIB_METADATA``
+can still be used to enable the implementation on 3.10 and earlier, or disable
+it on 3.11 (by setting it to ``0`` or ``false``).
diff --git a/src/pip/_internal/metadata/__init__.py b/src/pip/_internal/metadata/__init__.py
index aa9a80822..01c35f94b 100644
--- a/src/pip/_internal/metadata/__init__.py
+++ b/src/pip/_internal/metadata/__init__.py
@@ -1,7 +1,11 @@
+import contextlib
 import functools
 import os
+import sys
 from typing import TYPE_CHECKING, List, Optional, Type, cast
 
+from pip._internal.utils.misc import strtobool
+
 from .base import BaseDistribution, BaseEnvironment, FilesystemWheel, MemoryWheel, Wheel
 
 if TYPE_CHECKING:
@@ -22,6 +26,29 @@ __all__ = [
 ]
 
 
+def _should_use_importlib_metadata() -> bool:
+    """Whether to use the ``importlib.metadata`` or ``pkg_resources`` backend.
+
+    By default, pip uses ``importlib.metadata`` on Python 3.11+, and
+    ``pkg_resourcess`` otherwise. This can be overriden by a couple of ways:
+
+    * If environment variable ``_PIP_USE_IMPORTLIB_METADATA`` is set, it
+      dictates whether ``importlib.metadata`` is used, regardless of Python
+      version.
+    * On Python 3.11+, Python distributors can patch ``importlib.metadata``
+      to add a global constant ``_PIP_USE_IMPORTLIB_METADATA = False``. This
+      makes pip use ``pkg_resources`` (unless the user set the aforementioned
+      environment variable to *True*).
+    """
+    with contextlib.suppress(KeyError, ValueError):
+        return bool(strtobool(os.environ["_PIP_USE_IMPORTLIB_METADATA"]))
+    if sys.version_info < (3, 11):
+        return False
+    import importlib.metadata
+
+    return bool(getattr(importlib.metadata, "_PIP_USE_IMPORTLIB_METADATA", True))
+
+
 class Backend(Protocol):
     Distribution: Type[BaseDistribution]
     Environment: Type[BaseEnvironment]
@@ -29,7 +56,7 @@ class Backend(Protocol):
 
 @functools.lru_cache(maxsize=None)
 def select_backend() -> Backend:
-    if os.environ.get("_PIP_METADATA_BACKEND_IMPORTLIB"):
+    if _should_use_importlib_metadata():
         from . import importlib
 
         return cast(Backend, importlib)