MBM try-runtime support

[liamaharon]

MBM try-runtime support

This MR adds support to the try-runtime trait such that the try-runtime-CLI will be able to support MBM testing here. It mainly adds two feature-gated hooks to the SteppedMigration hook to facilitate testing. These hooks are named pre_upgrade and post_upgrade and have the same signature and implications as for single-block migrations.

Integration

To make use of this in your Multi-Block-Migration, just implement the two new hooks and test pre- and post-conditions in them:

#[cfg(feature = "try-runtime")]
fn pre_upgrade() -> Result<Vec<u8>, frame_support::sp_runtime::TryRuntimeError> {
	// ...
}

#[cfg(feature = "try-runtime")]
fn post_upgrade(prev: Vec<u8>) -> Result<(), frame_support::sp_runtime::TryRuntimeError> {
    // ...
}

You may return an error or panic in these functions to indicate failure. This will then show up in the try-runtime-CLI and can be used in CI for testing.

Changes:

• Adds try-runtime gated methods pre_upgrade and post_upgrade on SteppedMigration
• Adds try-runtime gated methods nth_pre_upgrade and nth_post_upgrade on SteppedMigrations
• Modifies pallet_migrations implementation to run pre_upgrade and post_upgrade steps at the appropriate times, and panic in the event of migration failure.

[bkchr]

I remember that you asked somewhere which approach to take. I would take the approach of building multiple blocks until the MBMs are finished. I know that this is more complicated, but this directly checks that your runtime can handle this properly and also that you stay always in the POV limits.

(Didn't check the pr yet :D)

[liamaharon]

I remember that you asked somewhere which approach to take. I would take the approach of building multiple blocks until the MBMs are finished. I know that this is more complicated, but this directly checks that your runtime can handle this properly and also that you stay always in the POV limits.

(Didn't check the pr yet :D)

Here's the discussion paritytech/try-runtime-cli#17 (comment)

I missed that Kian also supports building proper blocks. Although more involved, I will proceed with that approach :)

[georgepisaltu]

LGTM

[georgepisaltu]

Should be removed, right?

[georgepisaltu]

I think it's ok, it's just try-runtime storage.

[ggwpez]

Waiting for #5649 to merge as to not block the merge queue.

[alvicsam]

Would be nice to move this check to github action. If this is not urgent I can do it in this PR, if it's urgent - I can do it later.

[ggwpez]

I am trying to get it in soon since i then want to finally merge this #5676 without any conflicts. I enabled auto-merge last week, but apparently nothing happened.

I will re-try it one more time and if that does not work then i guess we have to move the check?