Remove deprecation warning from vendored pkg_resources (#12660)

Author: effigies

news/12660.trivial.rst

@@ -0,0 +1,2 @@
+Remove (suppressed) deprecation warning from vendored ``pkg_resources``
+to ensure builds succeed with ``PYTHONWARNINGS=error``.

src/pip/_vendor/pkg_resources/__init__.py

@@ -99,12 +99,10 @@
 _namespace_packages = None
 
 
-warnings.warn(
-    "pkg_resources is deprecated as an API. "
-    "See https://setuptools.pypa.io/en/latest/pkg_resources.html",
-    DeprecationWarning,
-    stacklevel=2,
-)
+# Patch: Remove deprecation warning from vendored pkg_resources.
+# Setting PYTHONWARNINGS=error to verify builds produce no warnings
+# causes immediate exceptions.
+# See https://github.com/pypa/pip/issues/12243
 
 
 _PEP440_FALLBACK = re.compile(r"^v?(?P<safe>(?:[0-9]+!)?[0-9]+(?:\.[0-9]+)*)", re.I)

tools/vendoring/patches/pkg_resources.patch

@@ -11,3 +11,22 @@ index 3f2476a0c..8d5727d35 100644
      yield_lines,
      drop_comment,
      join_continuation,
+--- a/src/pip/_vendor/pkg_resources/__init__.py
++++ b/src/pip/_vendor/pkg_resources/__init__.py
+@@ -101,12 +101,10 @@ _namespace_handlers = None
+ _namespace_packages = None
+
+
+-warnings.warn(
+-    "pkg_resources is deprecated as an API. "
+-    "See https://setuptools.pypa.io/en/latest/pkg_resources.html",
+-    DeprecationWarning,
+-    stacklevel=2,
+-)
++# Patch: Remove deprecation warning from vendored pkg_resources.
++# Setting PYTHONWARNINGS=error to verify builds produce no warnings
++# causes immediate exceptions.
++# See https://github.com/pypa/pip/issues/12243
+
+
+ _PEP440_FALLBACK = re.compile(r"^v?(?P<safe>(?:[0-9]+!)?[0-9]+(?:\.[0-9]+)*)", re.I)