fix checkout remote branch when branch name contains slash

jupyterlab_git/git.py

@@ -486,6 +486,13 @@ def remove_cell_ids(nb):
 
             return {"base": prev_nb, "diff": thediff}
 
+    async def _is_first_commit(self, path: str) -> bool:
+        """Return True if repo has no commits yet."""
+        code, _, _ = await self.__execute(
+            ["git", "rev-parse", "--verify", "HEAD"], cwd=path
+        )
+        return code != 0
+
     async def status(self, path: str) -> dict:
         """
         Execute git status command & return the result.
@@ -501,14 +508,19 @@ async def status(self, path: str) -> dict:
             }
 
         # Add attribute `is_binary`
-        command = [  # Compare stage to an empty tree see `_is_binary`
-            "git",
-            "diff",
-            "--numstat",
-            "-z",
-            "--cached",
-            "4b825dc642cb6eb9a060e54bf8d69288fbee4904",
-        ]
+        first_commit = await self._is_first_commit(path)
+        if first_commit:
+            # only first commit has to compare to an empty tree
+            command = [ # Compare stage to an empty tree see `_is_binary`
+                "git",
+                "diff",
+                "--numstat",
+                "-z",
+                "--cached",
+                "4b825dc642cb6eb9a060e54bf8d69288fbee4904",
+            ]
+        else:
+            command = ["git", "diff", "--numstat", "-z", "--cached"]
         text_code, text_output, _ = await self.__execute(command, cwd=path)
 
         are_binary = dict()
@@ -1137,7 +1149,7 @@ async def checkout_branch(self, branchname, path):
             is_remote_branch = self._is_remote_branch(reference_name)
 
         if is_remote_branch:
-            local_branchname = branchname.split("/")[-1]
+            local_branchname = "/".join(branchname.split("/")[1:])
             cmd = ["git", "checkout", "-B", local_branchname, branchname]
         else:
             cmd = ["git", "checkout", branchname]

jupyterlab_git/tests/test_branch.py

@@ -174,6 +174,48 @@ async def test_checkout_branch_remoteref_success():
             assert {"code": rc, "message": stdout_message} == actual_response
 
 
+@pytest.mark.asyncio
+async def test_checkout_branch_remoteref_success_when_has_slash():
+    branch = "origin/test-branch/test"
+    local_branch = "test-branch/test"
+    curr_path = str(Path("/bin/test_curr_path"))
+    stdout_message = "checkout output from git"
+    stderr_message = ""
+    rc = 0
+
+    with patch("jupyterlab_git.git.execute") as mock_execute:
+        with patch.object(
+            Git,
+            "_get_branch_reference",
+            return_value=maybe_future("refs/remotes/remote_branch"),
+        ) as mock__get_branch_reference:
+            # Given
+            mock_execute.return_value = maybe_future(
+                (rc, stdout_message, stderr_message)
+            )
+
+            # When
+            actual_response = await Git().checkout_branch(
+                branchname=branch, path=curr_path
+            )
+
+            # Then
+            mock__get_branch_reference.assert_has_calls([call(branch, curr_path)])
+
+            cmd = ["git", "checkout", "-B", local_branch, branch]
+            mock_execute.assert_called_once_with(
+                cmd,
+                cwd=str(Path("/bin") / "test_curr_path"),
+                timeout=20,
+                env=None,
+                username=None,
+                password=None,
+                is_binary=False,
+            )
+
+            assert {"code": rc, "message": stdout_message} == actual_response
+
+
 @pytest.mark.asyncio
 async def test_checkout_branch_headsref_failure():
     branch = "test-branch"