Revert "Remove importlib-metadata and importlib-resources"

This reverts commit 38435ae81c.

lib/importlib_metadata/_adapters.py

@@ -0,0 +1,90 @@
+import functools
+import warnings
+import re
+import textwrap
+import email.message
+
+from ._text import FoldedCase
+from ._compat import pypy_partial
+
+
+# Do not remove prior to 2024-01-01 or Python 3.14
+_warn = functools.partial(
+    warnings.warn,
+    "Implicit None on return values is deprecated and will raise KeyErrors.",
+    DeprecationWarning,
+    stacklevel=pypy_partial(2),
+)
+
+
+class Message(email.message.Message):
+    multiple_use_keys = set(
+        map(
+            FoldedCase,
+            [
+                'Classifier',
+                'Obsoletes-Dist',
+                'Platform',
+                'Project-URL',
+                'Provides-Dist',
+                'Provides-Extra',
+                'Requires-Dist',
+                'Requires-External',
+                'Supported-Platform',
+                'Dynamic',
+            ],
+        )
+    )
+    """
+    Keys that may be indicated multiple times per PEP 566.
+    """
+
+    def __new__(cls, orig: email.message.Message):
+        res = super().__new__(cls)
+        vars(res).update(vars(orig))
+        return res
+
+    def __init__(self, *args, **kwargs):
+        self._headers = self._repair_headers()
+
+    # suppress spurious error from mypy
+    def __iter__(self):
+        return super().__iter__()
+
+    def __getitem__(self, item):
+        """
+        Warn users that a ``KeyError`` can be expected when a
+        mising key is supplied. Ref python/importlib_metadata#371.
+        """
+        res = super().__getitem__(item)
+        if res is None:
+            _warn()
+        return res
+
+    def _repair_headers(self):
+        def redent(value):
+            "Correct for RFC822 indentation"
+            if not value or '\n' not in value:
+                return value
+            return textwrap.dedent(' ' * 8 + value)
+
+        headers = [(key, redent(value)) for key, value in vars(self)['_headers']]
+        if self._payload:
+            headers.append(('Description', self.get_payload()))
+        return headers
+
+    @property
+    def json(self):
+        """
+        Convert PackageMetadata to a JSON-compatible format
+        per PEP 0566.
+        """
+
+        def transform(key):
+            value = self.get_all(key) if key in self.multiple_use_keys else self[key]
+            if key == 'Keywords':
+                value = re.split(r'\s+', value)
+            tk = key.lower().replace('-', '_')
+            return tk, value
+
+        return dict(map(transform, map(FoldedCase, self)))