Allow using any polkadot client instead of enum Client (#1575)

* WIP

Forked at: e91642361133dba084a9c9b3efa45fcb6cd3c5ca
Parent branch: origin/rococo-branch

* WIP

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Parent branch: origin/rococo-branch

* WIP

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Parent branch: origin/rococo-branch

* WIP

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Parent branch: origin/rococo-branch

* WIP

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Parent branch: origin/rococo-branch

* WIP

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Parent branch: origin/rococo-branch

* WIP

Forked at: e91642361133dba084a9c9b3efa45fcb6cd3c5ca
Parent branch: origin/rococo-branch

* WIP

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Parent branch: origin/rococo-branch

* Apply suggestions from code review

* WIP

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Parent branch: origin/rococo-branch

* WIP

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Parent branch: origin/rococo-branch

* WIP

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* CLEANUP

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* link in doc

* doc

polkadot/service/src/client.rs

@@ -118,6 +118,19 @@ pub trait ExecuteWithClient {
 			Client: AbstractClient<Block, Backend, Api = Api> + 'static;
 }
 
+/// A handle to a Polkadot client instance.
+///
+/// The Polkadot service supports multiple different runtimes (Westend, Polkadot itself, etc). As each runtime has a
+/// specialized client, we need to hide them behind a trait. This is this trait.
+///
+/// When wanting to work with the inner client, you need to use `execute_with`.
+///
+/// See [`ExecuteWithClient`](trait.ExecuteWithClient.html) for more information.
+pub trait ClientHandle {
+	/// Execute the given something with the client.
+	fn execute_with<T: ExecuteWithClient>(&self, t: T) -> T::Output;
+}
+
 /// A client instance of Polkadot.
 ///
 /// See [`ExecuteWithClient`] for more information.
@@ -129,9 +142,8 @@ pub enum Client {
 	Rococo(Arc<crate::FullClient<rococo_runtime::RuntimeApi, crate::RococoExecutor>>),
 }
 
-impl Client {
-	/// Execute the given something with the client.
-	pub fn execute_with<T: ExecuteWithClient>(&self, t: T) -> T::Output {
+impl ClientHandle for Client {
+	fn execute_with<T: ExecuteWithClient>(&self, t: T) -> T::Output {
 		match self {
 			Self::Polkadot(client) => {
 				T::execute_with_client::<_, _, crate::FullBackend>(t, client.clone())

polkadot/service/src/lib.rs

@@ -109,16 +109,25 @@ impl IdentifyVariant for Box<dyn ChainSpec> {
 	}
 }
 
-type FullBackend = service::TFullBackend<Block>;
-type FullSelectChain = sc_consensus::LongestChain<FullBackend, Block>;
-type FullClient<RuntimeApi, Executor> = service::TFullClient<Block, RuntimeApi, Executor>;
-type FullGrandpaBlockImport<RuntimeApi, Executor> = grandpa::GrandpaBlockImport<
+/// Polkadot's full backend.
+pub type FullBackend = service::TFullBackend<Block>;
+
+/// Polkadot's select chain.
+pub type FullSelectChain = sc_consensus::LongestChain<FullBackend, Block>;
+
+/// Polkadot's full client.
+pub type FullClient<RuntimeApi, Executor> = service::TFullClient<Block, RuntimeApi, Executor>;
+
+/// Polkadot's full Grandpa block import.
+pub type FullGrandpaBlockImport<RuntimeApi, Executor> = grandpa::GrandpaBlockImport<
 	FullBackend, Block, FullClient<RuntimeApi, Executor>, FullSelectChain
 >;
 
-type LightBackend = service::TLightBackendWithHash<Block, sp_runtime::traits::BlakeTwo256>;
+/// Polkadot's light backend.
+pub type LightBackend = service::TLightBackendWithHash<Block, sp_runtime::traits::BlakeTwo256>;
 
-type LightClient<RuntimeApi, Executor> =
+/// Polkadot's light client.
+pub type LightClient<RuntimeApi, Executor> =
 	service::TLightClientWithBackend<Block, RuntimeApi, Executor, LightBackend>;
 
 #[cfg(feature = "full-node")]