dvc: get rid of is_walking_tree

No longer needed. Some applications of `isinstance()` will be refactored
in the future, as trees will just provide the needed functionality.

dvc/external_repo.py

@@ -20,7 +20,7 @@
 from dvc.repo import Repo
 from dvc.repo.tree import RepoTree
 from dvc.scm.git import Git
-from dvc.scm.tree import is_working_tree
+from dvc.tree.local import LocalRemoteTree
 from dvc.utils.fs import remove
 
 logger = logging.getLogger(__name__)
@@ -102,10 +102,8 @@ def repo_tree(self):
         return RepoTree(self, fetch=True)
 
     def get_rev(self):
-        if is_working_tree(self.tree):
+        if isinstance(self.tree, LocalRemoteTree):
             return self.scm.get_rev()
-        if hasattr(self.tree, "tree"):
-            return self.tree.tree.rev
         return self.tree.rev
 
     def fetch_external(self, paths: Iterable, **kwargs):

dvc/output/local.py

@@ -5,7 +5,6 @@
 from dvc.exceptions import DvcException
 from dvc.istextfile import istextfile
 from dvc.output.base import BaseOutput
-from dvc.scm.tree import is_working_tree
 from dvc.utils import relpath
 from dvc.utils.fs import path_isin
 
@@ -23,7 +22,11 @@ def __init__(self, stage, path, *args, **kwargs):
             path = relpath(path, stage.wdir)
 
         super().__init__(stage, path, *args, **kwargs)
-        if self.is_in_repo and self.repo and is_working_tree(self.repo.tree):
+        if (
+            self.is_in_repo
+            and self.repo
+            and isinstance(self.repo.tree, LocalRemoteTree)
+        ):
             self.tree = self.repo.tree
 
     def _parse_path(self, tree, path):

dvc/repo/diff.py

@@ -1,7 +1,7 @@
 import os
 
 from dvc.repo import locked
-from dvc.scm.tree import is_working_tree
+from dvc.tree.local import LocalRemoteTree
 
 
 @locked
@@ -33,7 +33,7 @@ def _to_path(output):
                 else os.path.join(str(output), "")
             )
 
-        on_working_tree = is_working_tree(self.tree)
+        on_working_tree = isinstance(self.tree, LocalRemoteTree)
 
         def _to_checksum(output):
             if on_working_tree: