Codegen output not implements codec::Decode

[boozook]

Some codegen output not implements codec::Decode.

To reproduce there's two runtimes metadata:
pontem.scale.zip

#[subxt::subxt(runtime_metadata_path = "nodes/pontem.scale")]
// or similar for pontem-xcmp.scale
pub mod pontem {}

Error: the trait Decode is not implemented for BTreeMap<pontem::runtime_types::polkadot_parachain::primitives::Id, MessageQueueChain>

build log errors

...
 error[E0277]: the trait bound `BTreeMap: Decode` is not satisfied
	--> src/main.rs:31:1
	 |
 31 | #[subxt::subxt(runtime_metadata_path = "nodes/pontem-xcmp.scale")]
	 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
	 | |
	 | the trait `Decode` is not implemented for `BTreeMap`
	 | in this procedural macro expansion
	 |
	::: ~/.cargo/git/checkouts/subxt-d8146022e5587204/78fd590/macro/src/lib.rs:39:1
	 |
 39 | pub fn subxt(args: TokenStream, input: TokenStream) -> TokenStream {
	 | ------------------------------------------------------------------ in this expansion of `#[subxt::subxt]`
	 |
	 = help: the following implementations were found:
				   as Decode>
 note: required by a bound in `subxt::StorageEntry::Value`
	--> ~/.cargo/git/checkouts/subxt-d8146022e5587204/78fd590/src/storage.rs:50:17
	 |
 50 |     type Value: Decode;
	 |                 ^^^^^^ required by this bound in `subxt::StorageEntry::Value`
error[E0277]: the trait bound BTreeMap<pontem::runtime_types::polkadot_parachain::primitives::Id, Vec<pontem::runtime_types::polkadot_core_primitives::InboundHrmpMessage<u32>>>: Decode is not satisfied

--> src/main.rs:31:1

|

31  | #[subxt::subxt(runtime_metadata_path = "nodes/pontem-xcmp.scale")]

| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

| |

| the trait Decode is not implemented for BTreeMap<pontem::runtime_types::polkadot_parachain::primitives::Id, Vec<pontem::runtime_types::polkadot_core_primitives::InboundHrmpMessage<u32>>>

| in this procedural macro expansion

|

::: ~/.cargo/git/checkouts/subxt-d8146022e5587204/78fd590/macro/src/lib.rs:39:1

|

39  | pub fn subxt(args: TokenStream, input: TokenStream) -> TokenStream {

| ------------------------------------------------------------------ in this expansion of #[subxt::subxt]

|

= help: the following implementations were found:

<BTreeMap<K, V> as Decode>

note: required by a bound in parity_scale_codec::Decode::decode

--> ~/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/parity-scale-codec-2.3.1/src/codec.rs:284:15

|

284 |     fn decode<I: Input>(input: &mut I) -> Result<Self, Error>;

|                  ^^^^^ required by this bound in parity_scale_codec::Decode::decode

[kvinwang]

workaround:

#[subxt::subxt(runtime_metadata_path = "nodes/pontem.scale")]
pub mod pontem {}
const _: () = {
    use pontem::runtime_types::polkadot_parachain::primitives::Id;

    impl PartialEq for Id {
        fn eq(&self, other: &Self) -> bool {
            self.0 == other.0
        }
    }

    impl Eq for Id {

    }

    impl PartialOrd for Id {
        fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
            self.0.partial_cmp(&other.0)
        }
    }

    impl Ord for Id {
        fn cmp(&self, other: &Self) -> std::cmp::Ordering {
            self.0.cmp(&other.0)
        }
    }
};

[ascjones]

Alternatively you might be able to use substitute_type and define a local Id type e.g.

#[derive(Eq, PartialEq, Encode, Decode)]
pub struct ParachainId ( .. );

#[subxt::subxt(runtime_metadata_path = "nodes/pontem.scale")]
pub mod pontem {
   #[subxt(substitute_type = "polkadot_parachain::primitives::Id")]
    use super::ParachainId;
}

That might work.

[jsdw]

I believe that this will be closed by #456; you'll no longer need the Ord trait when that lands.