fix(cli): do not start a session when in detached HEAD state

renku/core/session/session.py

@@ -158,6 +158,9 @@ def session_start(
     """
     from renku.domain_model.project_context import project_context
 
+    if project_context.repository.head.detached:
+        raise errors.SessionStartError("Cannot start a session from a detached HEAD. Check out a branch first.")
+
     # NOTE: The Docker client in Python requires the parameters below to be a list and will fail with a tuple.
     # Click will convert parameters with the flag "many" set to True to tuples.
     kwargs["security_opt"] = list(kwargs.get("security_opt", []))

renku/infrastructure/repository.py

@@ -1554,6 +1554,11 @@ def reference(self) -> Optional[Reference]:
         except (git.GitError, TypeError):
             return None
 
+    @property
+    def detached(self) -> bool:
+        """True if the reference is to a commit and not a branch."""
+        return self._reference.is_detached
+
 
 class RemoteReference(Reference):
     """A git remote reference."""
@@ -1681,8 +1686,11 @@ def set_url(self, url: str):
         _run_git_command(self._repository, "remote", "set-url", self.name, url)
 
     @property
-    def head(self) -> str:
+    def head(self) -> Optional[str]:
         """The head commit of the remote."""
+        if self._repository.head.is_detached:
+            return None
+
         self._remote.fetch()
         return _run_git_command(self._repository, "rev-parse", f"{self._remote.name}/{self._repository.active_branch}")
 

tests/cli/test_session.py

@@ -175,3 +175,18 @@ def test_session_list_format(runner, project, dummy_session_provider, format, ou
     assert 0 == result.exit_code, format_result_exception(result)
     assert length == len(result.output.splitlines())
     assert output in result.output
+
+
+def test_session_detached_start(runner, project, dummy_session_provider):
+    """Test starting a session in a detached HEAD repository."""
+    # NOTE: Make a dummy commit for project to have two commits
+    (project.repository.path / "README.md").write_text("changes")
+    project.repository.add(all=True)
+    project.repository.commit("dummy commit")
+
+    project.repository.checkout("HEAD~")
+
+    result = runner.invoke(cli, ["session", "start", "-p", "dummy"])
+
+    assert 1 == result.exit_code, format_result_exception(result)
+    assert "Cannot start a session from a detached HEAD" in result.output

tests/core/metadata/test_repository.py

@@ -326,3 +326,23 @@ def test_ignored_paths(paths, ignored, project):
     from renku.domain_model.project_context import project_context
 
     assert project_context.repository.get_ignored_paths(*paths) == ignored
+
+
+def test_remote(git_repository):
+    """Test get remote of a repository."""
+    assert 1 == len(git_repository.remotes)
+
+    remote = git_repository.remotes[0]
+
+    assert "origin" == remote.name
+    assert "8853e0c1112e512c36db9cc76faff560b655e5d5" == remote.head
+
+
+def test_remote_detached(git_repository):
+    """Test get remote of a repository with detached head."""
+    git_repository.checkout("HEAD~")
+
+    remote = git_repository.remotes[0]
+
+    assert "origin" == remote.name
+    assert remote.head is None