implement pygit2 backend for fetch_refspec

fix #168

1. Add order select for `_backend_func`.
2. Raise exception for fetch_refspec for ssh:// repo on Windows.
3. Add order select for _backend_func

setup.cfg

@@ -32,6 +32,7 @@ install_requires=
     pathspec>=0.9.0
     asyncssh>=2.7.1,<3
     funcy>=1.14
+    shortuuid>=0.5.0
 
 [options.extras_require]
 tests =

src/scmrepo/git/__init__.py

@@ -41,6 +41,8 @@ def __getitem__(self, key: str) -> BaseGitBackend:
         """Lazily initialize backends and cache it afterwards"""
         initialized = self.initialized.get(key)
         if not initialized:
+            if key not in self.backends and key in self.DEFAULT:
+                raise NotImplementedError
             backend = self.backends[key]
             initialized = backend(*self.args, **self.kwargs)
             self.initialized[key] = initialized
@@ -266,11 +268,13 @@ def no_commits(self):
     # https://github.com/iterative/dvc/issues/5641
     # https://github.com/iterative/dvc/issues/7458
     def _backend_func(self, name, *args, **kwargs):
-        for key, backend in self.backends.items():
+        backends: Iterable[str] = kwargs.pop("backends", self.backends)
+        for key in backends:
             if self._last_backend is not None and key != self._last_backend:
                 self.backends[self._last_backend].close()
                 self._last_backend = None
             try:
+                backend = self.backends[key]
                 func = getattr(backend, name)
                 result = func(*args, **kwargs)
                 self._last_backend = key
@@ -333,7 +337,9 @@ def add_commit(
     iter_remote_refs = partialmethod(_backend_func, "iter_remote_refs")
     get_refs_containing = partialmethod(_backend_func, "get_refs_containing")
     push_refspecs = partialmethod(_backend_func, "push_refspecs")
-    fetch_refspecs = partialmethod(_backend_func, "fetch_refspecs")
+    fetch_refspecs = partialmethod(
+        _backend_func, "fetch_refspecs", backends=["pygit2", "dulwich"]
+    )
     _stash_iter = partialmethod(_backend_func, "_stash_iter")
     _stash_push = partialmethod(_backend_func, "_stash_push")
     _stash_apply = partialmethod(_backend_func, "_stash_apply")

src/scmrepo/git/backend/pygit2.py

@@ -7,6 +7,8 @@
 from typing import (
     TYPE_CHECKING,
     Callable,
+    Dict,
+    Generator,
     Iterable,
     List,
     Mapping,
@@ -15,7 +17,8 @@
     Union,
 )
 
-from funcy import cached_property
+from funcy import cached_property, reraise
+from shortuuid import uuid
 
 from scmrepo.exceptions import CloneError, MergeConflictError, RevError, SCMError
 from scmrepo.utils import relpath
@@ -27,6 +30,8 @@
 
 
 if TYPE_CHECKING:
+    from pygit2.remote import Remote  # type: ignore
+
     from scmrepo.progress import GitProgressEvent
 
 
@@ -412,6 +417,52 @@ def push_refspecs(
     ) -> Mapping[str, SyncStatus]:
         raise NotImplementedError
 
+    def _merge_remote_branch(
+        self,
+        rh: str,
+        lh: str,
+        force: bool = False,
+        on_diverged: Optional[Callable[[str, str], bool]] = None,
+    ) -> SyncStatus:
+        import pygit2
+
+        rh_rev = self.resolve_rev(rh)
+
+        if force:
+            self.set_ref(lh, rh_rev)
+            return SyncStatus.SUCCESS
+
+        try:
+            merge_result, _ = self.repo.merge_analysis(rh_rev, lh)
+        except KeyError:
+            self.set_ref(lh, rh_rev)
+            return SyncStatus.SUCCESS
+
+        if merge_result & pygit2.GIT_MERGE_ANALYSIS_UP_TO_DATE:
+            return SyncStatus.UP_TO_DATE
+        if merge_result & pygit2.GIT_MERGE_ANALYSIS_FASTFORWARD:
+            self.set_ref(lh, rh_rev)
+            return SyncStatus.SUCCESS
+        if merge_result & pygit2.GIT_MERGE_ANALYSIS_NORMAL:
+            if on_diverged and on_diverged(lh, rh_rev):
+                return SyncStatus.SUCCESS
+            return SyncStatus.DIVERGED
+        logger.debug("Unexpected merge result: %s", pygit2.GIT_MERGE_ANALYSIS_NORMAL)
+        raise SCMError("Unknown merge analysis result")
+
+    @contextmanager
+    def get_remote(self, url: str) -> Generator["Remote", None, None]:
+        try:
+            yield self.repo.remotes[url]
+        except ValueError:
+            try:
+                remote_name = uuid()
+                yield self.repo.remotes.create(remote_name, url)
+            finally:
+                self.repo.remotes.delete(remote_name)
+        except KeyError:
+            raise SCMError(f"'{url}' is not a valid Git remote or URL")
+
     def fetch_refspecs(
         self,
         url: str,
@@ -421,7 +472,58 @@ def fetch_refspecs(
         progress: Callable[["GitProgressEvent"], None] = None,
         **kwargs,
     ) -> Mapping[str, SyncStatus]:
-        raise NotImplementedError
+        from pygit2 import GitError
+
+        if isinstance(refspecs, str):
+            refspecs = [refspecs]
+
+        with self.get_remote(url) as remote:
+            if os.name == "nt" and remote.url.startswith("ssh://"):
+                raise NotImplementedError
+
+            if os.name == "nt" and remote.url.startswith("file://"):
+                url = remote.url[len("file://") :]
+                self.repo.remotes.set_url(remote.name, url)
+                remote = self.repo.remotes[remote.name]
+
+            fetch_refspecs: List[str] = []
+            for refspec in refspecs:
+                if ":" in refspec:
+                    lh, rh = refspec.split(":")
+                else:
+                    lh = rh = refspec
+                if not rh.startswith("refs/"):
+                    rh = f"refs/heads/{rh}"
+                if not lh.startswith("refs/"):
+                    lh = f"refs/heads/{lh}"
+                rh = rh[len("refs/") :]
+                refspec = f"+{lh}:refs/remotes/{remote.name}/{rh}"
+                fetch_refspecs.append(refspec)
+
+            logger.debug("fetch_refspecs: %s", fetch_refspecs)
+            with reraise(
+                GitError,
+                SCMError(f"Git failed to fetch ref from '{url}'"),
+            ):
+                remote.fetch(refspecs=fetch_refspecs)
+
+            result: Dict[str, "SyncStatus"] = {}
+            for refspec in fetch_refspecs:
+                _, rh = refspec.split(":")
+                if not rh.endswith("*"):
+                    refname = rh.split("/", 3)[-1]
+                    refname = f"refs/{refname}"
+                    result[refname] = self._merge_remote_branch(
+                        rh, refname, force, on_diverged
+                    )
+                    continue
+                rh = rh.rstrip("*").rstrip("/") + "/"
+                for branch in self.iter_refs(base=rh):
+                    refname = f"refs/{branch[len(rh):]}"
+                    result[refname] = self._merge_remote_branch(
+                        branch, refname, force, on_diverged
+                    )
+        return result
 
     def _stash_iter(self, ref: str):
         raise NotImplementedError

tests/test_git.py

@@ -1,12 +1,14 @@
 import os
 import shutil
-from typing import Any, Dict, Optional, Type
+from typing import Any, Dict, List, Optional, Type
 
 import pytest
 from asyncssh import SFTPClient
 from asyncssh.connection import SSHClientConnection
 from dulwich.client import LocalGitClient
 from git import Repo as GitPythonRepo
+from pygit2 import GitError
+from pygit2.remote import Remote  # type: ignore
 from pytest_mock import MockerFixture
 from pytest_test_utils import TempDirFactory, TmpDir
 from pytest_test_utils.matchers import Matcher
@@ -306,7 +308,7 @@ def test_push_refspecs(
     assert remote_scm.get_ref("refs/foo/baz") is None
 
 
-@pytest.mark.skip_git_backend("pygit2", "gitpython")
+@pytest.mark.skip_git_backend("gitpython")
 @pytest.mark.parametrize("use_url", [True, False])
 def test_fetch_refspecs(
     tmp_dir: TmpDir,
@@ -362,8 +364,11 @@ def test_fetch_refspecs(
 
     with pytest.raises(SCMError):
         mocker.patch.object(LocalGitClient, "fetch", side_effect=KeyError)
+        mocker.patch.object(Remote, "fetch", side_effect=GitError)
         git.fetch_refspecs(remote, "refs/foo/bar:refs/foo/bar")
 
+    assert len(scm.pygit2.repo.remotes) == 1
+
 
 @pytest.mark.skip_git_backend("pygit2", "gitpython")
 @pytest.mark.parametrize("use_url", [True, False])
@@ -1046,3 +1051,22 @@ def test_is_dirty_untracked(
     tmp_dir.gen("untracked", "untracked")
     assert git.is_dirty(untracked_files=True)
     assert not git.is_dirty(untracked_files=False)
+
+
+@pytest.mark.parametrize(
+    "backends", [["gitpython", "dulwich"], ["dulwich", "gitpython"]]
+)
+def test_backend_func(
+    tmp_dir: TmpDir,
+    scm: Git,
+    backends: List[str],
+    mocker: MockerFixture,
+):
+    from functools import partial
+
+    scm.add = partial(scm._backend_func, "add", backends=backends)
+    tmp_dir.gen({"foo": "foo"})
+    backend = getattr(scm, backends[0])
+    mock = mocker.spy(backend, "add")
+    scm.add(["foo"])
+    mock.assert_called_once_with(["foo"])