Dask worker CLI error message might be misleading

[guillaumeeb]

Describe the issue:

Dask worker cli error message is not always helpful as it doesn't check for unknown options. It might be hard to understand what is wrong. (See discussion in https://dask.discourse.group/t/unexpected-dask-argument/3979).

Minimal Complete Verifiable Example:

dask worker --scheduler-file random_file --nprocs 1

outputs:

Usage: dask worker [OPTIONS] [SCHEDULER] [PRELOAD_ARGV]…
Try ‘dask worker -h’ for help.

Error: Got unexpected extra argument: (1)

Which is true: 1 is an argument, but in this case, a user wants to know that --nprocs is not a valid option.

Anything else we need to know?:

This is probably due to the need to have a preload free argv in the dask worker command. So options are not enforced in click.

I'd be happy to help, but I'm not a click expert and I'm not sure of the side effects of enabling options checking.