scm: add force parameter to checkout() (iterative#5582)

The `GitPythonBackend.checkout()` method already implicitly supported
this by forwarding `**kwargs` to the backend. `pygit2` didn't support
this yet.

This patch fixes this inconsistency.

dvc/scm/git/backend/base.py

@@ -67,7 +67,11 @@ def commit(self, msg: str, no_verify: bool = False):
 
     @abstractmethod
     def checkout(
-        self, branch: str, create_new: Optional[bool] = False, **kwargs,
+        self,
+        branch: str,
+        create_new: Optional[bool] = False,
+        force: bool = False,
+        **kwargs,
     ):
         pass
 

dvc/scm/git/backend/dulwich.py

@@ -189,7 +189,11 @@ def commit(self, msg: str, no_verify: bool = False):
             raise SCMError("Git commit failed") from exc
 
     def checkout(
-        self, branch: str, create_new: Optional[bool] = False, **kwargs,
+        self,
+        branch: str,
+        create_new: Optional[bool] = False,
+        force: bool = False,
+        **kwargs,
     ):
         raise NotImplementedError
 

dvc/scm/git/backend/gitpython.py

@@ -217,12 +217,16 @@ def commit(self, msg: str, no_verify: bool = False):
             raise SCMError("Git pre-commit hook failed") from exc
 
     def checkout(
-        self, branch: str, create_new: Optional[bool] = False, **kwargs
+        self,
+        branch: str,
+        create_new: Optional[bool] = False,
+        force: bool = False,
+        **kwargs,
     ):
         if create_new:
-            self.repo.git.checkout("HEAD", b=branch, **kwargs)
+            self.repo.git.checkout("HEAD", b=branch, force=force, **kwargs)
         else:
-            self.repo.git.checkout(branch, **kwargs)
+            self.repo.git.checkout(branch, force=force, **kwargs)
 
     def pull(self, **kwargs):
         infos = self.repo.remote().pull(**kwargs)

dvc/scm/git/backend/pygit2.py

@@ -100,22 +100,28 @@ def commit(self, msg: str, no_verify: bool = False):
         raise NotImplementedError
 
     def checkout(
-        self, branch: str, create_new: Optional[bool] = False, **kwargs,
+        self,
+        branch: str,
+        create_new: Optional[bool] = False,
+        force: bool = False,
+        **kwargs,
     ):
-        from pygit2 import GitError
+        from pygit2 import GIT_CHECKOUT_FORCE, GitError
+
+        checkout_strategy = GIT_CHECKOUT_FORCE if force else None
 
         if create_new:
             commit = self.repo.revparse_single("HEAD")
             new_branch = self.repo.branches.local.create(branch, commit)
-            self.repo.checkout(new_branch)
+            self.repo.checkout(new_branch, strategy=checkout_strategy)
         else:
             if branch == "-":
                 branch = "@{-1}"
             try:
                 commit, ref = self.repo.resolve_refish(branch)
             except (KeyError, GitError):
                 raise RevError(f"unknown Git revision '{branch}'")
-            self.repo.checkout_tree(commit)
+            self.repo.checkout_tree(commit, strategy=checkout_strategy)
             detach = kwargs.get("detach", False)
             if ref and not detach:
                 self.repo.set_head(ref.name)