How to migrate to metadataV14

Question

I have a live network working on Substrate V3 and MetadataV12. How can I migrate to the MetadataV14?

The MetadataV14 is a part of the Substrate V4. Unfortunately Substrate V4 isn't released.

Answer 1

To migrate your chain to the V14 metadata system, follow these steps (from this upgrade guide):

1. Remove any #[pallet::metadata(..)] attributes from your pallet's Event definition.
2. Add scale-info as a dependency to your pallet and runtime crates:

• scale-info = { version = "1.0.0", default-features = false, features = ["derive"] }
• std = [ "scale-info/std" ]

3. Derive scale_info::TypeInfo for any types which derive Decode, Encode(*). For example:

#[derive(Encode, Decode, Clone, PartialEq, Eq, RuntimeDebug, TypeInfo)]
struct HeartbeatStatus<BlockNumber> {
    pub session_index: SessionIndex,
    pub sent_at: BlockNumber,
}

4. Update any pallet Call variant constructors to use named structs (previously unnamed tuple structs).
5. Update the metadata runtime API call:

impl sp_api::Metadata<Block> for Runtime {
    fn metadata() -> OpaqueMetadata {
        OpaqueMetadata::new(Runtime::metadata().into())
    }
}

(*) If the type is in a separate crate to the pallet, add the scale-info dependency as above.