Runtime API compilation error after adding Runtime API metadata.

[koushiro]

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Description of bug

When I upgrade substrate version of my project ( polkadot-v0.9.39 ==> polkadot-v0.9.42 ), the runtime API I originally defined will compile with an error:

➜  api-demo git:(master) cargo build --release
    Updating git repository `https:/paritytech/substrate`
    Updating crates.io index
   Compiling api-demo v0.1.0 (/Users/koushiro/api-demo)
error[E0277]: the trait bound `C: ProposalConfig` is not satisfied
  --> src/lib.rs:22:1
   |
22 | / sp_api::decl_runtime_apis! {
23 | |     pub trait DemoApi<C>
24 | |     where
25 | |         C: ProposalConfig,
...  |
28 | |     }
29 | | }
   | |_^ the trait `ProposalConfig` is not implemented for `C`
   |
   = note: this error originates in the macro `sp_api::decl_runtime_apis` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider further restricting type parameter `C`
   |
29 | }, C: ProposalConfig
   |  +++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.
error: could not compile `api-demo` due to previous error

I think it should be caused by #13302 .

Steps to reproduce

The simple repo to reproduce the issue.

stable-aarch64-apple-darwin (default)
rustc 1.69.0 (84c898d65 2023-04-16)

[package]
name = "api-demo"
version = "0.1.0"
edition = "2021"

[dependencies]
scale-codec = { package = "parity-scale-codec", version = "3.5.0", default-features = false }
scale-info = { version = "2.7.0", default-features = false }

sp-api = { git = "https:/paritytech/substrate", branch = "polkadot-v0.9.42", default-features = false }
sp-runtime = { git = "https:/paritytech/substrate", branch = "polkadot-v0.9.42", default-features = false }
sp-std = { git = "https:/paritytech/substrate", branch = "polkadot-v0.9.42", default-features = false }

[features]
default = ["std"]
std = [
    "scale-codec/std",
    "scale-info/std",
    "sp-api/std",
    "sp-runtime/std",
    "sp-std/std",
]

#![cfg_attr(not(feature = "std"), no_std)]

use scale_codec::{Codec, Decode, Encode};
use scale_info::TypeInfo;
// Substrate
use sp_runtime::{traits::Member, RuntimeDebug};
use sp_std::hash::Hash;

pub trait ProposalConfig {
    type ProposalNumber: Member + Codec + Into<u64> + From<u32> + Copy + Hash + Ord;
}

pub type ProposalNumberOf<T> = <T as ProposalConfig>::ProposalNumber;

pub type VotingStatusOf<C> = VotingStatus<ProposalNumberOf<C>>;

#[derive(Clone, PartialEq, RuntimeDebug, Encode, Decode, TypeInfo)]
pub struct VotingStatus<PNumber> {
    pub last_processed_number: Option<PNumber>,
}

sp_api::decl_runtime_apis! {
    pub trait DemoApi<C>
    where
        C: ProposalConfig,
    {
        fn voting_status() -> VotingStatusOf<C>;
    }
}

[koushiro]

@lexnv PTAL

[bkchr]

Found the issue, we don't forward the where bound properly. Let me quickly fix this.