@@ -149,14 +149,30 @@ class Diffable:
149149 :const:`git.NULL_TREE` and :const:`git.diff.NULL_TREE`.
150150 """
151151
152- INDEX = Index = INDEX
152+ INDEX = INDEX
153153"""Stand-in indicating you want to diff against the index.
154154
155155 See the :meth:`diff` method, which accepts this as a value of its ``other``
156156 parameter.
157157
158158 This is the same as :const:`DiffConstants.INDEX`, and may also be accessed as
159- :const:`git.INDEX` and :const:`git.diff.INDEX`.
159+ :const:`git.INDEX` and :const:`git.diff.INDEX`, as well as :class:`Diffable.INDEX`,
160+ which is kept for backward compatibility (it is now defined an alias of this).
161+ """
162+
163+ Index = INDEX
164+ """Stand-in indicating you want to diff against the index
165+ (same as :const:`~Diffable.INDEX`).
166+
167+ This is an alias of :const:`~Diffable.INDEX`, for backward compatibility. See
168+ :const:`~Diffable.INDEX` and :meth:`diff` for details.
169+
170+ :note:
171+ Although always meant for use as an opaque constant, this was formerly defined
172+ as a class. Its usage is unchanged, but static type annotations that attempt
173+ to permit only this object must be changed to avoid new mypy errors. This was
174+ previously not possible to do, though ``Type[Diffable.Index]`` approximated it.
175+ It is now possible to do precisely, using ``Literal[DiffConstants.INDEX]``.
160176 """
161177
162178def _process_diff_args (
@@ -213,10 +229,9 @@ def diff(
213229 A :class:`DiffIndex` representing the computed diff.
214230
215231 :note:
216- On a bare repository, `other` needs to be provided as
217- :class:`~Diffable.Index`, or as an instance of
218- :class:`~git.objects.tree.Tree` or :class:`~git.objects.commit.Commit`, or a
219- git command error will occur.
232+ On a bare repository, `other` needs to be provided as :const:`INDEX`, or as
233+ an instance of :class:`~git.objects.tree.Tree` or
234+ :class:`~git.objects.commit.Commit`, or a git command error will occur.
220235 """
221236args :List [Union [PathLike ,Diffable ]]= []
222237args .append ("--abbrev=40" )# We need full shas.