v4.0.0-rc0

This release includes v1 of the Fee Middleware module. 🍾 Please read the introduction blog post and the documentation!

It also bumps the Go version to v1.18 and the Cosmos SDK to v0.45.6 (for more information, see Cosmos SDK v0.45.6 Release Notes), and introduces several improvements and bug fixes. We present here a summary of the most relevant changes, but please see the v4.0.0 changelog for the full set of changes included in this pre-release.

core/04-channel

• The OnChanOpenInit application callback now returns a version string in line with the latest spec change.
• The NewErrorAcknowledgement function accepts now an error instead of a string, removing therefore the possibility of non-deterministic writes to application state. Please read the relevant section in the migration documentation for more details.

apps/transfer

• The NewErrorAcknowledgement function has been removed in favour of 04-channel's NewErrorAcknowledgement.

apps/27-interchain-accounts

• The RegisterInterchainAccount function includes now an additional version argument to support ICS29 fee middleware functionality in ICS27 interchain accounts. Please read the relevant section in the documentation for more information.
• The NewErrorAcknowledgement function has been removed in favour of 04-channel's NewErrorAcknowledgement.

Special thanks to our external contributors on this release: @faddat @vuong177

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To learn more about ibc-go versioning, please read our RELEASES.md.

IMPORTANT: Please read the migration guides for any versions of ibc-go that you might be going through when upgrading to this version. For example: if you upgrade from the IBC module contained in the Cosmos SDK 0.42.0 to SDK v0.45.6 and ibc-go v4.0.0-rc0, please follow:

1. The migration from SDK 0.41.x or 0.42.x to the IBC module in the ibc-go repository based on the SDK v0.44.x.
2. The migration from ibc-go v1 to v2.
3. The migration from ibc-go v2 to v3.
4. The migration from ibc-go v3 to v4.
5. The migration to add support for transfers of tokens whose base denomination contains slashes.