traceback: no tasks

[oliver-sanders]

This example validates:

[scheduling]
    [[graph]]
        R1 = """
            # no comment
        """

But if you tried to run it:

data_store_mgr.py", line 841, in generate_definition_elements
        workflow.tree_depth = max([
                              ^^^^^
    ValueError: max() iterable argument is empty

Yikes!

Ideally:

• Cylc validate would catch the empty graph and fail.
• The data store would be robust against a workflow with no tasks.

[hjoliver]

Arguably a workflow with no tasks is valid - the scheduler should successfully start up, run no tasks, and shut down. Not sure I can think of a use case for that though!

[matthewrmshin]

Sorry, it was me who accidentally ran a command to start up a workflow that would result in no tasks, as the workflow would normally use rose optional configurations to inject Jinja2 variables to add tasks to the workflow. It took me a while to realise my mistake as I thought the workflow passed cylc validate. It would be nice if cylc validate can catch/warn that the workflow has no tasks.

[dwsutherland]

Arguably a workflow with no tasks is valid - the scheduler should successfully start up, run no tasks, and shut down. Not sure I can think of a use case for that though!

[wxtim]

We already mark such a workflow as invalid. It's just that the check requires the graph definition to be empty of everything, even comments.

[oliver-sanders]

tldr; make cylc validate fail for this example.