utils: implement path_isin to compare child and parent paths

dvc/utils/fs.py

@@ -134,3 +134,14 @@ def remove(path):
     except OSError as exc:
         if exc.errno != errno.ENOENT:
             raise
+
+
+def path_isin(child, parent):
+    """Check if given `child` path is inside `parent`."""
+
+    def normalize_path(path):
+        return os.path.normpath(fspath(path))
+
+    parent = os.path.join(normalize_path(parent), "")
+    child = normalize_path(child)
+    return child != parent and child.startswith(parent)

tests/unit/utils/test_fs.py

@@ -16,7 +16,7 @@
 from dvc.utils.fs import get_inode
 from dvc.utils.fs import get_mtime_and_size
 from dvc.utils.fs import move
-from dvc.utils.fs import remove
+from dvc.utils.fs import path_isin, remove
 from tests.basic_env import TestDir
 from tests.utils import spy
 
@@ -164,3 +164,49 @@ def test_remove(repo_dir):
 
     remove(path_info)
     assert not os.path.isfile(path_info.fspath)
+
+
+@pytest.mark.parametrize(
+    "parent",
+    [
+        (os.path.join("path", "to", "")),
+        (os.path.join("path", "to")),
+        (os.path.join("path", "")),
+        (os.path.join("path")),
+    ],
+)
+def test_path_isin_positive(parent):
+    child = os.path.join("path", "to", "folder")
+    assert path_isin(child, parent)
+
+
+def test_path_isin_on_same_path():
+    path = os.path.join("path", "to", "folder")
+    path2 = os.path.join(path, "")
+
+    assert not path_isin(path, path)
+    assert not path_isin(path, path2)
+    assert not path_isin(path2, path)
+    assert not path_isin(path2, path2)
+
+
+def test_path_isin_on_common_substring_path():
+    path1 = os.path.join("path", "to", "folder1")
+    path2 = os.path.join("path", "to", "folder")
+
+    assert not path_isin(path1, path2)
+
+
+def test_path_isin_accepts_pathinfo():
+    child = os.path.join("path", "to", "folder")
+    parent = PathInfo(child) / ".."
+
+    assert path_isin(child, parent)
+    assert not path_isin(parent, child)
+
+
+def test_path_isin_with_absolute_path():
+    parent = os.path.abspath("path")
+    child = os.path.join(parent, "to", "folder")
+
+    assert path_isin(child, parent)