Make IndexFile and Diffable .diff() types agree

Author: Yobmod

git/diff.py

@@ -20,6 +20,7 @@
 
 if TYPE_CHECKING:
     from .objects.tree import Tree
+    from .objects import Commit
     from git.repo.base import Repo
     from git.objects.base import IndexObject
     from subprocess import Popen
@@ -90,7 +91,7 @@ def _process_diff_args(self, args: List[Union[PathLike, 'Diffable', Type['Diffab
             Subclasses can use it to alter the behaviour of the superclass"""
         return args
 
-    def diff(self, other: Union[Type['Index'], 'Tree', None, str] = Index,
+    def diff(self, other: Union[Type['Index'], 'Tree', 'Commit', None, str] = Index,  # object for git.NULL_TREE
              paths: Union[PathLike, List[PathLike], Tuple[PathLike, ...], None] = None,
              create_patch: bool = False, **kwargs: Any) -> 'DiffIndex':
         """Creates diffs between two items being trees, trees and index or an

git/index/base.py

@@ -1273,7 +1273,8 @@ def reset(self, commit: Union[Commit, 'Reference', str] = 'HEAD', working_tree:
 
     # @ default_index, breaks typing for some reason, copied into function
     def diff(self,
-             other: Union[git_diff.Diffable.Index, 'IndexFile.Index', Treeish, None, object] = git_diff.Diffable.Index,
+             other: Union[Type['git_diff.Diffable.Index'], 'IndexFile.Index',
+                          'Tree', 'Commit', str, None] = git_diff.Diffable.Index,
              paths: Union[PathLike, List[PathLike], Tuple[PathLike, ...], None] = None,
              create_patch: bool = False, **kwargs: Any
              ) -> git_diff.DiffIndex: