Deprecate XCMv3

[bkontur]

Now that we have XCMv5 released, we should deprecate XCMv3, similar to how we deprecated XCMv2 when we introduced XCMv4.

TODO

• Deprecate XCMv3
• Check, fix, or remove MIN_XCM_VERSION – see comment here
• Backport to all stable2412 and stable2503 versions (should be fine, as Fellows has migrated to xcm::v4 – reference

[xlc]

why backport to existing stable versions?

[bkchr]

Yeah and we should also not remove the code if not really needed.

[bkontur]

why backport to existing stable versions?

my mistake - not to all, but only to those containing XCMv5 (stable2412, stable2503). I think we should backport Deprecate XCMv3 so that downstream users upgrade in advance (kind of forcing them to migrate to XCMv4 or XCMv5).

@franciscoaguirre Do we have documentation somewhere on adding new XCM versions and the deprecation process? I think I saw it "somewhere"?

Yeah and we should also not remove the code if not really needed.

MIN_XCM_VERSION was introduced/merged just last week, and I believe it is not really needed to expose it from xcm module.

[xlc]

Is there a v4 / v5 migration guide? I have no idea where to look up for guides.

I tried search v5 on this page and there is no result? https://github.com/paritytech/polkadot-sdk/releases?page=1

[programskillforverification]

I would like to work on this. Please assign to me.

[bkontur]

@franciscoaguirre @raymondkfcheung wdyt?

[franciscoaguirre]

There is still no guide for migrating from v4 to v5, I'm working on it.
If MIN_XCM_VERSION is only used for tests, let's remove it.
We should move on with deprecating v3 and backporting it to stable2412 and stable2503. We can't support old versions of XCM indefinitely.

[bkchr]

We can't support old versions of XCM indefinitely.

Why? Can we not convert them to XCMv4 and then execute it?