Make has_repo protocol runtime checkable and use in Diffable

3 files changed, 27 insertions, 10 deletions

diff --git a/git/config.py b/git/config.py
index 19ce1f84..2c863f93 100644
--- a/git/config.py
+++ b/git/config.py
@@ -234,8 +234,8 @@ def get_config_path(config_level: Lit_config_levels) -> str:
     elif config_level == "repository":
         raise ValueError("No repo to get repository configuration from. Use Repo._get_config_path")
     else:
-        # Should not reach here. Will raise ValueError if does. Static typing will warn about extra and missing elifs
-        assert_never(config_level, ValueError("Invalid configuration level: %r" % config_level))
+        # Should not reach here. Will raise ValueError if does. Static typing will warn missing elifs
+        assert_never(config_level, ValueError(f"Invalid configuration level: {config_level!r}"))
 
 
 class GitConfigParser(with_metaclass(MetaParserBuilder, cp.RawConfigParser, object)):  # type: ignore ## mypy does not understand dynamic class creation # noqa: E501
diff --git a/git/diff.py b/git/diff.py
index d3b18652..cb216299 100644
--- a/git/diff.py
+++ b/git/diff.py
@@ -16,7 +16,7 @@ from .objects.util import mode_str_to_int
 # typing ------------------------------------------------------------------
 
 from typing import Any, Iterator, List, Match, Optional, Tuple, Type, TypeVar, Union, TYPE_CHECKING
-from git.types import PathLike, TBD, Literal, TypeGuard
+from git.types import Has_Repo, PathLike, TBD, Literal, TypeGuard
 
 if TYPE_CHECKING:
     from .objects.tree import Tree
@@ -141,8 +141,10 @@ class Diffable(object):
         if paths is not None and not isinstance(paths, (tuple, list)):
             paths = [paths]
 
-        if hasattr(self, 'repo'):  # else raise Error?
-            self.repo = self.repo  # type: 'Repo'
+        if isinstance(self, Has_Repo):
+            self.repo: Repo = self.repo
+        else:
+            raise AttributeError("No repo member found, cannot create DiffIndex")
 
         diff_cmd = self.repo.git.diff
         if other is self.Index:
diff --git a/git/types.py b/git/types.py
index b107c2e1..9181e040 100644
--- a/git/types.py
+++ b/git/types.py
@@ -4,7 +4,7 @@
 
 import os
 import sys
-from typing import (Callable, Dict, NoReturn, Tuple, Union, Any, Iterator,       # noqa: F401
+from typing import (Callable, Dict, NoReturn, Sequence, Tuple, Union, Any, Iterator,       # noqa: F401
                     NamedTuple, TYPE_CHECKING, TypeVar)       # noqa: F401
 
 if TYPE_CHECKING:
@@ -37,6 +37,8 @@ _T = TypeVar('_T')
 Tree_ish = Union['Commit', 'Tree']
 Commit_ish = Union['Commit', 'TagObject', 'Blob', 'Tree']
 
+# Config_levels ---------------------------------------------------------
+
 Lit_config_levels = Literal['system', 'global', 'user', 'repository']
 
 
@@ -47,12 +49,25 @@ def is_config_level(inp: str) -> TypeGuard[Lit_config_levels]:
 
 ConfigLevels_Tup = Tuple[Literal['system'], Literal['user'], Literal['global'], Literal['repository']]
 
+#-----------------------------------------------------------------------------------
+
+
+def assert_never(inp: NoReturn, raise_error: bool = True, exc: Union[Exception, None] = None) -> None:
+    """For use in exhaustive checking of literal or Enum in if/else chain.
+    Should only be reached if all memebers not handled OR attempt to pass non-members through chain.
+
+    If all members handled, type is Empty. Otherwise, will cause mypy error.
+    If non-members given, should cause mypy error at variable creation.
 
-def assert_never(inp: NoReturn, exc: Union[Exception, None] = None) -> NoReturn:
-    if exc is None:
-        assert False, f"An unhandled Literal ({inp}) in an if/else chain was found"
+    If raise_error is True, will also raise AssertionError or the Exception passed to exc.
+    """
+    if raise_error:
+        if exc is None:
+            raise ValueError(f"An unhandled Literal ({inp}) in an if/else chain was found")
+        else:
+            raise exc
     else:
-        raise exc
+        pass
 
 
 class Files_TD(TypedDict):