dulwich: use SubprocessSSHVendor when necessary

src/scmrepo/git/backend/dulwich/__init__.py

@@ -98,14 +98,32 @@ def write(self, msg: Union[str, bytes]) -> int:
 
 
 def _get_ssh_vendor() -> "SSHVendor":
+    import sys
+
     from dulwich.client import SubprocessSSHVendor
 
-    from .asyncssh_vendor import AsyncSSHVendor
+    from .asyncssh_vendor import AsyncSSHVendor, get_unsupported_opts
 
     ssh_command = os.environ.get("GIT_SSH_COMMAND", os.environ.get("GIT_SSH"))
     if ssh_command:
         logger.debug("dulwich: Using environment GIT_SSH_COMMAND '%s'", ssh_command)
         return SubprocessSSHVendor()
+
+    if sys.platform == "win32" and os.environ.get("MSYSTEM"):
+        # see https://github.com/iterative/dvc/issues/7702
+        logger.debug(
+            "dulwich: native win32 Python inside MSYS2/git-bash, using MSYS2 OpenSSH"
+        )
+        return SubprocessSSHVendor()
+
+    default_config = os.path.expanduser(os.path.join("~", ".ssh", "config"))
+    unsupported = list(get_unsupported_opts([default_config]))
+    if unsupported:
+        logger.debug(
+            "dulwich: unsupported SSH config option(s) '%s', using system OpenSSH",
+            ", ".join(unsupported),
+        )
+        return SubprocessSSHVendor()
     return AsyncSSHVendor()
 
 

src/scmrepo/git/backend/dulwich/asyncssh_vendor.py

@@ -1,13 +1,24 @@
 """asyncssh SSH vendor for Dulwich."""
 import asyncio
-from typing import TYPE_CHECKING, Callable, Coroutine, List, Optional
+from typing import (
+    TYPE_CHECKING,
+    Callable,
+    Coroutine,
+    Iterator,
+    List,
+    Optional,
+    Sequence,
+)
 
 from dulwich.client import SSHVendor
 
 from scmrepo.asyn import BaseAsyncObject, sync_wrapper
 from scmrepo.exceptions import AuthError
 
 if TYPE_CHECKING:
+    from pathlib import Path
+
+    from asyncssh.config import ConfigPaths, FilePath
     from asyncssh.connection import SSHClientConnection
     from asyncssh.process import SSHClientProcess
     from asyncssh.stream import SSHReader
@@ -172,3 +183,51 @@ async def _run_command(
         return AsyncSSHWrapper(conn, proc)
 
     run_command = sync_wrapper(_run_command)
+
+
+# class ValidatedSSHClientConfig(SSHClientConfig):
+#     pass
+
+
+def get_unsupported_opts(config_paths: "ConfigPaths") -> Iterator[str]:
+    from pathlib import Path, PurePath
+
+    if config_paths:
+        if isinstance(config_paths, (str, PurePath)):
+            paths: Sequence["FilePath"] = [config_paths]
+        else:
+            paths = config_paths
+
+        for path in paths:
+            try:
+                yield from _parse_unsupported(Path(path))
+            except FileNotFoundError:
+                continue
+
+
+def _parse_unsupported(path: "Path") -> Iterator[str]:
+    import locale
+    import shlex
+
+    from asyncssh.config import SSHClientConfig
+
+    handlers = SSHClientConfig._handlers  # pylint: disable=protected-access
+    with open(path, encoding=locale.getpreferredencoding()) as fobj:
+        for line in fobj:
+            line = line.strip()
+            if not line or line[0] == "#":
+                continue
+
+            try:
+                args = shlex.split(line)
+            except ValueError:
+                continue
+
+            option = args.pop(0)
+            if option.endswith("="):
+                option = option[:-1]
+            elif "=" in option:
+                option, _ = option.split("=", 1)
+            loption = option.lower()
+            if loption not in handlers:
+                yield loption

tests/test_dulwich.py

@@ -1,3 +1,4 @@
+import os
 import socket
 import threading
 from io import StringIO
@@ -157,3 +158,43 @@ def test_dulwich_github_compat(mocker: MockerFixture, algorithm: bytes):
     strings = iter((b"ssh-rsa", key_data))
     packet.get_string = lambda: next(strings)
     _process_public_key_ok_gh(auth, None, None, packet)
+
+
+@pytest.mark.skipif(os.name != "nt", reason="Windows only")
+def test_git_bash_ssh_vendor(mocker):
+    from dulwich.client import SubprocessSSHVendor
+
+    from scmrepo.git.backend.dulwich import _get_ssh_vendor
+
+    mocker.patch.dict(os.environ, {"MSYSTEM": "MINGW64"})
+    assert isinstance(_get_ssh_vendor(), SubprocessSSHVendor)
+
+    del os.environ["MSYSTEM"]
+    assert isinstance(_get_ssh_vendor(), AsyncSSHVendor)
+
+
+def test_unsupported_config_ssh_vendor():
+    from dulwich.client import SubprocessSSHVendor
+
+    from scmrepo.git.backend.dulwich import _get_ssh_vendor
+
+    config = os.path.expanduser(os.path.join("~", ".ssh", "config"))
+    os.makedirs(os.path.dirname(config), exist_ok=True)
+
+    with open(config, "wb") as fobj:
+        fobj.write(
+            b"""
+Host *
+    IdentityFile ~/.ssh/id_rsa
+"""
+        )
+    assert isinstance(_get_ssh_vendor(), AsyncSSHVendor)
+
+    with open(config, "wb") as fobj:
+        fobj.write(
+            b"""
+Host *
+    UseKeychain yes
+"""
+        )
+    assert isinstance(_get_ssh_vendor(), SubprocessSSHVendor)