Revert "Remove importlib-metadata and importlib-resources"

This reverts commit 38435ae81c.

lib/importlib_resources/_compat.py

@@ -0,0 +1,109 @@
+# flake8: noqa
+
+import abc
+import os
+import sys
+import pathlib
+from contextlib import suppress
+from typing import Union
+
+
+if sys.version_info >= (3, 10):
+    from zipfile import Path as ZipPath  # type: ignore
+else:
+    from zipp import Path as ZipPath  # type: ignore
+
+
+try:
+    from typing import runtime_checkable  # type: ignore
+except ImportError:
+
+    def runtime_checkable(cls):  # type: ignore
+        return cls
+
+
+try:
+    from typing import Protocol  # type: ignore
+except ImportError:
+    Protocol = abc.ABC  # type: ignore
+
+
+class TraversableResourcesLoader:
+    """
+    Adapt loaders to provide TraversableResources and other
+    compatibility.
+
+    Used primarily for Python 3.9 and earlier where the native
+    loaders do not yet implement TraversableResources.
+    """
+
+    def __init__(self, spec):
+        self.spec = spec
+
+    @property
+    def path(self):
+        return self.spec.origin
+
+    def get_resource_reader(self, name):
+        from . import readers, _adapters
+
+        def _zip_reader(spec):
+            with suppress(AttributeError):
+                return readers.ZipReader(spec.loader, spec.name)
+
+        def _namespace_reader(spec):
+            with suppress(AttributeError, ValueError):
+                return readers.NamespaceReader(spec.submodule_search_locations)
+
+        def _available_reader(spec):
+            with suppress(AttributeError):
+                return spec.loader.get_resource_reader(spec.name)
+
+        def _native_reader(spec):
+            reader = _available_reader(spec)
+            return reader if hasattr(reader, 'files') else None
+
+        def _file_reader(spec):
+            try:
+                path = pathlib.Path(self.path)
+            except TypeError:
+                return None
+            if path.exists():
+                return readers.FileReader(self)
+
+        return (
+            # local ZipReader if a zip module
+            _zip_reader(self.spec)
+            or
+            # local NamespaceReader if a namespace module
+            _namespace_reader(self.spec)
+            or
+            # local FileReader
+            _file_reader(self.spec)
+            or
+            # native reader if it supplies 'files'
+            _native_reader(self.spec)
+            or
+            # fallback - adapt the spec ResourceReader to TraversableReader
+            _adapters.CompatibilityFiles(self.spec)
+        )
+
+
+def wrap_spec(package):
+    """
+    Construct a package spec with traversable compatibility
+    on the spec/loader/reader.
+
+    Supersedes _adapters.wrap_spec to use TraversableResourcesLoader
+    from above for older Python compatibility (<3.10).
+    """
+    from . import _adapters
+
+    return _adapters.SpecLoaderAdapter(package.__spec__, TraversableResourcesLoader)
+
+
+if sys.version_info >= (3, 9):
+    StrPath = Union[str, os.PathLike[str]]
+else:
+    # PathLike is only subscriptable at runtime in 3.9+
+    StrPath = Union[str, "os.PathLike[str]"]