Migration guide for Substrate Metadata V14

substrate-metadata-v14-migration.md

Substrate Runtime Builders

When updating to use the latest Substrate with V14 metadata, your runtime will fail to compile.

The following steps are required to make your pallets/runtime compatible. The compiler will guide you...

• Remove any #[pallet::metadata(..)] attributes from the pallet Event definition.
• Add scale-info dependency to pallet and runtime crates:
  • scale-info = { version = "1.0.0", default-features = false, features = ["derive"] }
  • std = [ "scale-info/std" ]
• Derive scale_info::TypeInfo for any types which derive Decode, Encode.
  • If the type is in a separate crate to the pallet, add the scale-info dependency as above.
• Update any pallet Call variant constructors to use named structs (previously unnamed tuple structs).
• Update the metadata runtime API call:

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

See the cumulus and polkadot PRs (linked below) for examples of the above conversion.

Resources

• Substrate PR: paritytech/substrate#8615
• Polkadot PR: paritytech/polkadot#3336
• Cumulus PR: paritytech/cumulus#564
• scale-info repo: https://github.com/paritytech/scale-info/
• frame-metadata repo: https://github.com/paritytech/frame-metadata/

Shouldn't scale-info version be 1.0?

Indeed it should be, Updated.

I would like to add that you should add #[scale_info(skip_type_params(T))] for structs which lazily use the pallet's Config as generic such as pub struct Example<T: Config> - if this statement is correct. This would have saved me quite some time when debugging our upgrade to 0.9.11 😅

We should surface this here: polkadot-developers/substrate-docs#385