Omit CWD in search for bash.exe to run hooks on Windows

This uses the same NoDefaultCurrentDirectoryInExePath technique for
the Popen call in git.index.fun.run_commit_hook on Windows as is
already used in git.cmd.Git.execute.

The code is simpler in run_commit_hook because a shell is never
used to run bash.exe. (bash.exe is itself a shell, but we never
run it *via* a shell by passing shell=True to Popen.) Nonetheless,
it may make sense to extract out a helper function both can call.
This commit does not do that, so there is some code duplication.

Author: EliahKagan

git/index/fun.py

@@ -3,6 +3,7 @@
 
 """Standalone functions to accompany the index implementation and make it more versatile."""
 
+import contextlib
 from io import BytesIO
 import os
 import os.path as osp
@@ -26,7 +27,7 @@
     traverse_trees_recursive,
     tree_to_stream,
 )
-from git.util import IndexFileSHA1Writer, finalize_process
+from git.util import IndexFileSHA1Writer, finalize_process, patch_env
 from gitdb.base import IStream
 from gitdb.typ import str_tree_type
 
@@ -90,6 +91,10 @@ def run_commit_hook(name: str, index: "IndexFile", *args: str) -> None:
     env = os.environ.copy()
     env["GIT_INDEX_FILE"] = safe_decode(str(index.path))
     env["GIT_EDITOR"] = ":"
+    if os.name == "nt":
+        maybe_patch_caller_env = patch_env("NoDefaultCurrentDirectoryInExePath", "1")
+    else:
+        maybe_patch_caller_env = contextlib.nullcontext()
     cmd = [hp]
     try:
         if os.name == "nt" and not _has_file_extension(hp):
@@ -98,14 +103,15 @@ def run_commit_hook(name: str, index: "IndexFile", *args: str) -> None:
             relative_hp = Path(hp).relative_to(index.repo.working_dir).as_posix()
             cmd = ["bash.exe", relative_hp]
 
-        process = subprocess.Popen(
-            cmd + list(args),
-            env=env,
-            stdout=subprocess.PIPE,
-            stderr=subprocess.PIPE,
-            cwd=index.repo.working_dir,
-            creationflags=PROC_CREATIONFLAGS,
-        )
+        with maybe_patch_caller_env:
+            process = subprocess.Popen(
+                cmd + list(args),
+                env=env,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE,
+                cwd=index.repo.working_dir,
+                creationflags=PROC_CREATIONFLAGS,
+            )
     except Exception as ex:
         raise HookExecutionError(hp, ex) from ex
     else: