git: add pygit2 skeleton (#5138)

Implements stuff we need for the tree, but this is more to start filling
up pygit2 with something useful.

dvc/scm/git/__init__.py

@@ -20,6 +20,7 @@ from dvc.utils.serialize import modify_yaml
 from .backend.base import NoGitBackendError
 from .backend.dulwich import DulwichBackend
 from .backend.gitpython import GitPythonBackend
+from .backend.pygit2 import Pygit2Backend
 from .stash import Stash
 
 logger = logging.getLogger(__name__)
@@ -31,7 +32,11 @@ class Git(Base):
     GITIGNORE = ".gitignore"
     GIT_DIR = ".git"
     DEFAULT_BACKENDS = OrderedDict(
-        [("dulwich", DulwichBackend), ("gitpython", GitPythonBackend)]
+        [
+            ("dulwich", DulwichBackend),
+            ("pygit2", Pygit2Backend),
+            ("gitpython", GitPythonBackend),
+        ]
     )
     LOCAL_BRANCH_PREFIX = "refs/heads/"
 
@@ -64,6 +69,10 @@ class Git(Base):
     def dulwich(self):
         return self.backends["dulwich"]
 
+    @property
+    def pygit2(self):
+        return self.backends["pygit2"]
+
     @cached_property
     def stash(self):
         return Stash(self)

dvc/scm/git/backend/pygit2.py

@@ -0,0 +1,231 @@
+import locale
+import logging
+import os
+from io import BytesIO, StringIO
+from typing import Callable, Iterable, Optional, Tuple
+
+from dvc.scm.base import SCMError
+
+from ..objects import GitObject
+from .base import BaseGitBackend
+
+logger = logging.getLogger(__name__)
+
+
+class Pygit2Object(GitObject):
+    def __init__(self, obj):
+        self.obj = obj
+
+    def open(self, mode: str = "r", encoding: str = None):
+        if not encoding:
+            encoding = locale.getpreferredencoding(False)
+        data = self.obj.read_raw()
+        if mode == "rb":
+            return BytesIO(data)
+        return StringIO(data.decode(encoding))
+
+    @property
+    def name(self) -> str:
+        return self.obj.name
+
+    @property
+    def mode(self):
+        return self.obj.filemode
+
+    def scandir(self) -> Iterable["Pygit2Object"]:
+        for entry in self.obj:  # noqa: B301
+            yield Pygit2Object(entry)
+
+
+class Pygit2Backend(BaseGitBackend):  # pylint:disable=abstract-method
+    def __init__(  # pylint:disable=W0231
+        self, root_dir=os.curdir, search_parent_directories=True
+    ):
+        import pygit2
+
+        if search_parent_directories:
+            ceiling_dirs = ""
+        else:
+            ceiling_dirs = os.path.abspath(root_dir)
+
+        # NOTE: discover_repository will return path/.git/
+        path = pygit2.discover_repository(  # pylint:disable=no-member
+            root_dir, True, ceiling_dirs
+        )
+        if not path:
+            raise SCMError(f"{root_dir} is not a git repository")
+
+        self.repo = pygit2.Repository(path)
+
+        self._stashes: dict = {}
+
+    def close(self):
+        self.repo.free()
+
+    @property
+    def root_dir(self) -> str:
+        return self.repo.workdir
+
+    @staticmethod
+    def clone(
+        url: str,
+        to_path: str,
+        rev: Optional[str] = None,
+        shallow_branch: Optional[str] = None,
+    ):
+        raise NotImplementedError
+
+    @staticmethod
+    def is_sha(rev: str) -> bool:
+        raise NotImplementedError
+
+    @property
+    def dir(self) -> str:
+        raise NotImplementedError
+
+    def add(self, paths: Iterable[str]):
+        raise NotImplementedError
+
+    def commit(self, msg: str):
+        raise NotImplementedError
+
+    def checkout(
+        self, branch: str, create_new: Optional[bool] = False, **kwargs,
+    ):
+        raise NotImplementedError
+
+    def pull(self, **kwargs):
+        raise NotImplementedError
+
+    def push(self):
+        raise NotImplementedError
+
+    def branch(self, branch: str):
+        raise NotImplementedError
+
+    def tag(self, tag: str):
+        raise NotImplementedError
+
+    def untracked_files(self) -> Iterable[str]:
+        raise NotImplementedError
+
+    def is_tracked(self, path: str) -> bool:
+        raise NotImplementedError
+
+    def is_dirty(self, **kwargs) -> bool:
+        raise NotImplementedError
+
+    def active_branch(self) -> str:
+        raise NotImplementedError
+
+    def list_branches(self) -> Iterable[str]:
+        raise NotImplementedError
+
+    def list_tags(self) -> Iterable[str]:
+        raise NotImplementedError
+
+    def list_all_commits(self) -> Iterable[str]:
+        raise NotImplementedError
+
+    def get_tree_obj(self, rev: str, **kwargs) -> Pygit2Object:
+        tree = self.repo[rev].tree
+        return Pygit2Object(tree)
+
+    def get_rev(self) -> str:
+        raise NotImplementedError
+
+    def resolve_rev(self, rev: str) -> str:
+        raise NotImplementedError
+
+    def resolve_commit(self, rev: str) -> str:
+        raise NotImplementedError
+
+    def branch_revs(self, branch: str, end_rev: Optional[str] = None):
+        raise NotImplementedError
+
+    def _get_stash(self, ref: str):
+        raise NotImplementedError
+
+    def is_ignored(self, path):
+        raise NotImplementedError
+
+    def set_ref(
+        self,
+        name: str,
+        new_ref: str,
+        old_ref: Optional[str] = None,
+        message: Optional[str] = None,
+        symbolic: Optional[bool] = False,
+    ):
+        raise NotImplementedError
+
+    def get_ref(self, name, follow: Optional[bool] = True) -> Optional[str]:
+        raise NotImplementedError
+
+    def remove_ref(self, name: str, old_ref: Optional[str] = None):
+        raise NotImplementedError
+
+    def iter_refs(self, base: Optional[str] = None):
+        raise NotImplementedError
+
+    def get_refs_containing(self, rev: str, pattern: Optional[str] = None):
+        raise NotImplementedError
+
+    def push_refspec(
+        self,
+        url: str,
+        src: Optional[str],
+        dest: str,
+        force: bool = False,
+        on_diverged: Optional[Callable[[str, str], bool]] = None,
+    ):
+        raise NotImplementedError
+
+    def fetch_refspecs(
+        self,
+        url: str,
+        refspecs: Iterable[str],
+        force: Optional[bool] = False,
+        on_diverged: Optional[Callable[[bytes, bytes], bool]] = None,
+    ):
+        raise NotImplementedError
+
+    def _stash_iter(self, ref: str):
+        raise NotImplementedError
+
+    def _stash_push(
+        self,
+        ref: str,
+        message: Optional[str] = None,
+        include_untracked: Optional[bool] = False,
+    ) -> Tuple[Optional[str], bool]:
+        raise NotImplementedError
+
+    def _stash_apply(self, rev: str):
+        raise NotImplementedError
+
+    def reflog_delete(
+        self, ref: str, updateref: bool = False, rewrite: bool = False
+    ):
+        raise NotImplementedError
+
+    def describe(
+        self,
+        rev: str,
+        base: Optional[str] = None,
+        match: Optional[str] = None,
+        exclude: Optional[str] = None,
+    ) -> Optional[str]:
+        raise NotImplementedError
+
+    def diff(self, rev_a: str, rev_b: str, binary=False) -> str:
+        raise NotImplementedError
+
+    def reset(self, hard: bool = False, paths: Iterable[str] = None):
+        raise NotImplementedError
+
+    def checkout_paths(self, paths: Iterable[str], force: bool = False):
+        raise NotImplementedError
+
+    def iter_remote_refs(self, url: str, base: Optional[str] = None):
+        raise NotImplementedError

setup.py

@@ -51,6 +51,7 @@ install_requires = [
     "configobj>=5.0.6",
     "gitpython>3",
     "dulwich>=0.20.14",
+    "pygit2>=1.4.0",
     "setuptools>=34.0.0",
     "nanotime>=0.5.2",
     "pyasn1>=0.4.1",