Correct Windows hook Bash precedence

git/index/fun.py

@@ -26,7 +26,7 @@
 from gitdb.base import IStream
 from gitdb.typ import str_tree_type
 
-from git.cmd import handle_process_output, safer_popen
+from git.cmd import Git, handle_process_output, safer_popen
 from git.compat import defenc, force_bytes, force_text, safe_decode
 from git.exc import HookExecutionError, UnmergedEntriesError
 from git.objects.fun import (
@@ -79,6 +79,97 @@ def _has_file_extension(path: str) -> str:
     return osp.splitext(path)[1]
 
 
+def _is_in_windows_system_root(path: str) -> bool:
+    """Return whether ``path`` is inside the Windows installation directory."""
+    system_root = os.environ.get("SystemRoot")
+    if not system_root:
+        return False
+
+    system_root = osp.normcase(osp.realpath(system_root))
+    path = osp.normcase(osp.realpath(path))
+    try:
+        return osp.commonpath((system_root, path)) == system_root
+    except ValueError:
+        # Paths on different drives have no common path on Windows.
+        return False
+
+
+def _which_from_path(command: str) -> Union[str, None]:
+    """Resolve ``command`` from PATH, excluding the Windows installation."""
+    for directory in os.get_exec_path():
+        # Unlike POSIX, Windows does not define an empty PATH entry as the current
+        # directory. Skip it rather than letting abspath() turn it into one.
+        if not directory:
+            continue
+        directory = osp.abspath(directory)
+        candidate = osp.join(directory, command)
+        # SystemRoot contains the WSL launcher stubs. They are valid executables but
+        # not suitable for running a Windows Git hook: the hook path and environment
+        # were prepared for Git for Windows, and WSL may have no distribution at all.
+        if _is_in_windows_system_root(candidate):
+            continue
+        if osp.isfile(candidate) and os.access(candidate, os.X_OK):
+            return candidate
+    return None
+
+
+_GIT_FOR_WINDOWS_PREFIXES = ("mingw64", "mingw32", "clangarm64", "clang64", "clang32", "ucrt64")
+
+
+def _git_for_windows_root() -> Union[str, None]:
+    """Infer a standard Git for Windows root from GitPython's selected executable."""
+    git_executable = os.fspath(Git.GIT_PYTHON_GIT_EXECUTABLE or Git.git_exec_name)
+    if osp.dirname(git_executable):
+        # CreateProcess resolves a relative executable path containing a directory
+        # from the parent process cwd, even when Popen supplies a different child cwd.
+        git_executable = osp.abspath(git_executable)
+    else:
+        # GitPython deliberately retains a bare executable name so later PATH changes
+        # affect Git commands. Resolve it with the same PATH snapshot used for Bash.
+        names = (git_executable,) if _has_file_extension(git_executable) else (git_executable, f"{git_executable}.exe")
+        for name in names:
+            resolved = _which_from_path(name)
+            if resolved is not None:
+                git_executable = resolved
+                break
+        else:
+            git_executable = ""
+    if not git_executable:
+        return None
+
+    executable_dir = osp.dirname(git_executable)
+    directory_name = osp.basename(executable_dir).lower()
+    if directory_name == "cmd":
+        # The normal system-wide PATH entry is <git-root>/cmd.
+        return osp.dirname(executable_dir)
+    if directory_name == "bin":
+        prefix = osp.dirname(executable_dir)
+        if osp.basename(prefix).lower() in _GIT_FOR_WINDOWS_PREFIXES:
+            # Git Bash commonly exposes <git-root>/<platform>/bin/git.exe.
+            return osp.dirname(prefix)
+        if osp.basename(prefix).lower() != "usr":
+            # An explicitly configured Git may be the root-level bin/git.exe. Do
+            # not make the same inference from usr/bin: unlike the recognized
+            # platform prefixes, "usr" has no reliably bounded parent layout.
+            return prefix
+    return None
+
+
+def _git_for_windows_bash() -> Union[str, None]:
+    """Return Bash from the Git for Windows installation selected by GitPython."""
+    git_root = _git_for_windows_root()
+    if git_root is None:
+        return None
+
+    # Match gix-path's precedence: prefer the lightweight bin shim, then the
+    # underlying usr/bin executable. Both belong to the same installation as Git.
+    for relative_path in ("bin/bash.exe", "usr/bin/bash.exe"):
+        candidate = osp.join(git_root, *relative_path.split("/"))
+        if osp.isfile(candidate) and os.access(candidate, os.X_OK):
+            return candidate
+    return None
+
+
 def run_commit_hook(name: str, index: "IndexFile", *args: str) -> None:
     """Run the commit hook of the given name. Silently ignore hooks that do not exist.
 
@@ -112,7 +203,12 @@ def run_commit_hook(name: str, index: "IndexFile", *args: str) -> None:
                 # an absolute path in this form, although a relative path is preferable
                 # because it also works with the Windows Subsystem for Linux wrapper.
                 bash_hp = hp
-            cmd = ["bash.exe", Path(bash_hp).as_posix()]
+            # Prefer Bash associated with GitPython's selected Git installation. If
+            # that layout is not recognized, use an explicitly configured non-system
+            # PATH entry. Preserve the bare fallback for installations that previously
+            # relied on WSL or another CreateProcess-resolved Bash.
+            bash_executable = _git_for_windows_bash() or _which_from_path("bash.exe") or "bash.exe"
+            cmd = [bash_executable, Path(bash_hp).as_posix()]
 
         process = safer_popen(
             cmd + list(args),

test/test_index.py

@@ -33,7 +33,7 @@
     UnmergedEntriesError,
     UnsafeOptionError,
 )
-from git.index.fun import hook_path, run_commit_hook
+from git.index.fun import _git_for_windows_bash, _which_from_path, hook_path, run_commit_hook
 from git.index.typ import BaseIndexEntry, IndexEntry
 from git.index.util import TemporaryFileSwap
 from git.objects import Blob
@@ -1128,16 +1128,65 @@ def test_run_commit_hook_outside_worktree_on_windows(self, rw_dir):
         repo = Repo.init(root / "repo")
         hooks_dir = root / "hooks"
         _make_hook(root, "fake-hook", "exit 0")
+        system_root = root / "Windows"
+        system_bash = system_root / "System32" / "bash.exe"
+        git_executable = root / "Git" / "cmd" / "git.exe"
+        git_bash = root / "Git" / "bin" / "bash.exe"
+        for executable in (system_bash, git_executable, git_bash):
+            executable.parent.mkdir(parents=True)
+            executable.touch()
+            executable.chmod(0o755)
         with repo.config_writer() as writer:
             writer.set_value("core", "hooksPath", str(hooks_dir))
 
-        with mock.patch("git.index.fun.sys.platform", "win32"):
+        # Model a normal Windows PATH: System32 (containing the WSL launcher) comes
+        # before Git's cmd directory, while Git's Bash is not itself on PATH. This
+        # exercises both Git-installation discovery and shell selection without
+        # mocking either resolver's answer.
+        with mock.patch("git.index.fun.sys.platform", "win32"), mock.patch.object(
+            Git, "GIT_PYTHON_GIT_EXECUTABLE", "git"
+        ), mock.patch.dict(os.environ, {"SystemRoot": str(system_root)}), mock.patch(
+            "git.index.fun.os.get_exec_path", return_value=["", str(system_bash.parent), str(git_executable.parent)]
+        ):
             with mock.patch("git.index.fun.safer_popen") as popen, mock.patch("git.index.fun.handle_process_output"):
                 popen.return_value.returncode = 0
                 run_commit_hook("fake-hook", repo.index)
 
         command = popen.call_args[0][0]
-        self.assertEqual(command, ["bash.exe", "../hooks/fake-hook"])
+        self.assertEqual(command, [str(git_bash), "../hooks/fake-hook"])
+
+    @with_rw_directory
+    def test_windows_bash_lookup_respects_explicit_current_directory_in_path(self, rw_dir):
+        root = Path(rw_dir).resolve()
+        bash = root / "bash.exe"
+        bash.touch()
+        bash.chmod(0o755)
+
+        # An explicitly listed directory is trusted PATH configuration, even when
+        # it happens to be the current directory. This differs from an empty entry,
+        # which Windows requires PATH lookup to ignore.
+        with cwd(root), mock.patch("git.index.fun.os.get_exec_path", return_value=[str(root)]):
+            self.assertEqual(_which_from_path("bash.exe"), str(bash))
+
+    @with_rw_directory
+    def test_windows_bash_lookup_from_explicit_git_bin(self, rw_dir):
+        git_root = Path(rw_dir).resolve() / "Git"
+        git_executable = git_root / "bin" / "git.exe"
+        bash = git_root / "bin" / "bash.exe"
+        git_executable.parent.mkdir(parents=True)
+        for executable in (git_executable, bash):
+            executable.touch()
+            executable.chmod(0o755)
+
+        # A relative executable containing a directory is resolved by CreateProcess
+        # from the parent process cwd, not the separately supplied child cwd. Enter the
+        # temporary root first because Windows cannot express a relative path between
+        # drives, and CI may keep the checkout and its temporary directory on different
+        # drives.
+        with cwd(Path(rw_dir).resolve()):
+            relative_git = osp.relpath(git_executable, os.curdir)
+            with mock.patch.object(Git, "GIT_PYTHON_GIT_EXECUTABLE", relative_git):
+                self.assertEqual(_git_for_windows_bash(), str(bash))
 
     @ddt.data((False,), (True,))
     @with_rw_directory