handle version change on restart (resume)

[oliver-sanders]

cylc restart (soon to be renamed cylc play) currently [8.0a3.dev] restarts a workflow using whatever version of Cylc is selected by the current environment.

For many this is a departure from rose suite-restart which sets the CYLC_VERSION to the version of the previous run. This old behaviour has an upside and a downside in that whist it ensures a compatible Cylc version is selected, it prohibits restarts from benefiting from bug fixes in maintainance releases.

Note: This issue does not cover the configuration of a Cylc version or compatible version range for a workflow which is a different matter (#3780 may provide a mechanism for this).

Proposal:

Note: for version 8.1.2 (major=8, minor=1, maintainance=2)

Edit 2021-11-29: Re worded to avoid confusion.

• Restart normally if the restart would:
  • Not change the version.
  • Increase the maintenance number.
• Prompt (override with --yes) for confirmation if the restart would:
  • Reduce the maintenance number.
  • Increase the minor number.
• Exit with nasty error (override with --force or --yes --yes?) if the restart would:
  • Decrease the minor number.
  • Change the major number.

Thoughts?

Pull requests welcome!

[hjoliver]

All good, except:

Block restart if the new Cylc version is lower than that of the previous run.

Not sure about a total block. How about prompt the user for confirmation but with a sterner warning of possible consequences.

[MetRonnie]

Possibly there could be cylc play --force option to override a block?

[oliver-sanders]

That's what the "(require an override to bypass)" was meant to mean, some sort of --force option.

[oliver-sanders]

Note this issue isn't completely critical for 8.0.0 as it wouldn't come into effect until the release after 8.0.0

[oliver-sanders]

Re worded the proposal to avoid confusion.