Add deprecation warning for non utf-8

pkg_resources/__init__.py

@@ -3323,14 +3323,33 @@ def _initialize_master_working_set():
     globals().update(locals())
 
 
-#  ---- Ported from ``setuptools`` to avoid introducing dependencies ----
+#  ---- Ported from ``setuptools`` to avoid introducing an import inter-dependency ----
 LOCALE_ENCODING = "locale" if sys.version_info >= (3, 10) else None
 
 
 def _read_utf8_with_fallback(file: str, fallback_encoding=LOCALE_ENCODING) -> str:
+    """See setuptools.unicode_utils._read_utf8_with_fallback"""
     try:
         with open(file, "r", encoding="utf-8") as f:
             return f.read()
     except UnicodeDecodeError:  # pragma: no cover
+        msg = f"""\
+        ********************************************************************************
+        `encoding="utf-8"` fails with {file!r}, trying `encoding={fallback_encoding!r}`.
+
+        This fallback behaviour is considered **deprecated** and future versions of
+        `setuptools/pkg_resources` may not implement it.
+
+        Please encode {file!r} with "utf-8" to ensure future builds will succeed.
+
+        If this file was produced by `setuptools` itself, cleaning up the cached files
+        and re-building/re-installing the package with a newer version of `setuptools`
+        (e.g. by updating `build-system.requires` in its `pyproject.toml`)
+        might solve the problem.
+        ********************************************************************************
+        """
+        # TODO: Add a deadline?
+        #       See comment in setuptools.unicode_utils._Utf8EncodingNeeded
+        warnings.warns(msg, PkgResourcesDeprecationWarning, stacklevel=2)
         with open(file, "r", encoding=fallback_encoding) as f:
             return f.read()

setuptools/command/setopt.py

@@ -6,7 +6,7 @@
 import configparser
 
 from .. import Command
-from ..compat import py39
+from ..unicode_utils import _cfg_read_utf8_with_fallback
 
 __all__ = ['config_file', 'edit_config', 'option_base', 'setopt']
 
@@ -37,12 +37,7 @@ def edit_config(filename, settings, dry_run=False):
     log.debug("Reading configuration from %s", filename)
     opts = configparser.RawConfigParser()
     opts.optionxform = lambda x: x
-
-    try:
-        opts.read([filename], encoding="utf-8")
-    except UnicodeDecodeError:  # pragma: no cover
-        opts.clear()
-        opts.read([filename], encoding=py39.LOCALE_ENCODING)
+    _cfg_read_utf8_with_fallback(opts, filename)
 
     for section, options in settings.items():
         if options is None:

setuptools/package_index.py

@@ -40,8 +40,7 @@
 from setuptools.wheel import Wheel
 from setuptools.extern.more_itertools import unique_everseen
 
-from .compat import py39
-from .unicode_utils import _read_utf8_with_fallback
+from .unicode_utils import _read_utf8_with_fallback, _cfg_read_utf8_with_fallback
 
 
 EGG_FRAGMENT = re.compile(r'^egg=([-A-Za-z0-9_.+!]+)$')
@@ -1014,11 +1013,7 @@ def __init__(self):
 
         rc = os.path.join(os.path.expanduser('~'), '.pypirc')
         if os.path.exists(rc):
-            try:
-                self.read(rc, encoding="utf-8")
-            except UnicodeDecodeError:  # pragma: no cover
-                self.clean()
-                self.read(rc, encoding=py39.LOCALE_ENCODING)
+            _cfg_read_utf8_with_fallback(self, rc)
 
     @property
     def creds_by_repository(self):

setuptools/unicode_utils.py

@@ -1,7 +1,9 @@
 import unicodedata
 import sys
+from configparser import ConfigParser
 
 from .compat import py39
+from .warnings import SetuptoolsDeprecationWarning
 
 
 # HFS Plus uses decomposed UTF-8
@@ -57,5 +59,44 @@ def _read_utf8_with_fallback(file: str, fallback_encoding=py39.LOCALE_ENCODING)
         with open(file, "r", encoding="utf-8") as f:
             return f.read()
     except UnicodeDecodeError:  # pragma: no cover
+        _Utf8EncodingNeeded.emit(file=file, fallback_encoding=fallback_encoding)
         with open(file, "r", encoding=fallback_encoding) as f:
             return f.read()
+
+
+def _cfg_read_utf8_with_fallback(
+    cfg: ConfigParser, file: str, fallback_encoding=py39.LOCALE_ENCODING
+) -> str:
+    """Same idea as :func:`_read_utf8_with_fallback`, but for the
+    :meth:`ConfigParser.read` method.
+
+    This method may call ``cfg.clear()``.
+    """
+    try:
+        cfg.read(file, encoding="utf-8")
+    except UnicodeDecodeError:  # pragma: no cover
+        _Utf8EncodingNeeded.emit(file=file, fallback_encoding=fallback_encoding)
+        cfg.clear()
+        cfg.read(file, encoding=fallback_encoding)
+
+
+class _Utf8EncodingNeeded(SetuptoolsDeprecationWarning):
+    _SUMMARY = """
+    `encoding="utf-8"` fails with {file!r}, trying `encoding={fallback_encoding!r}`.
+    """
+
+    _DETAILS = """
+    Fallback behaviour for UTF-8 is considered **deprecated** and future versions of
+    `setuptools` may not implement it.
+
+    Please encode {file!r} with "utf-8" to ensure future builds will succeed.
+
+    If this file was produced by `setuptools` itself, cleaning up the cached files
+    and re-building/re-installing the package with a newer version of `setuptools`
+    (e.g. by updating `build-system.requires` in its `pyproject.toml`)
+    might solve the problem.
+    """
+    # TODO: Add a deadline?
+    #       Will we be able to remove this?
+    #       The question comes to mind mainly because of sdists that have been produced
+    #       by old versions of setuptools and published to PyPI...