Simplify runtime api error handling (#8114)

* Ahh

* Work work work

* Fix all the compilation errors

* Fix test

* More fixes...

substrate/bin/node/executor/tests/common.rs

@@ -99,7 +99,7 @@ pub fn executor() -> NativeExecutor<Executor> {
 
 pub fn executor_call<
 	R:Decode + Encode + PartialEq,
-	NC: FnOnce() -> std::result::Result<R, String> + std::panic::UnwindSafe
+	NC: FnOnce() -> std::result::Result<R, Box<dyn std::error::Error + Send + Sync>> + std::panic::UnwindSafe
 >(
 	t: &mut TestExternalities<BlakeTwo256>,
 	method: &str,

substrate/client/api/src/call_executor.rs

@@ -78,7 +78,7 @@ pub trait CallExecutor<B: BlockT> {
 			Result<NativeOrEncoded<R>, Self::Error>
 		) -> Result<NativeOrEncoded<R>, Self::Error>,
 		R: Encode + Decode + PartialEq,
-		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+		NC: FnOnce() -> result::Result<R, sp_api::ApiError> + UnwindSafe,
 	>(
 		&self,
 		initialize_block_fn: IB,

substrate/client/authority-discovery/src/lib.rs

@@ -93,7 +93,7 @@ where
 	Block: BlockT + Unpin + 'static,
 	Network: NetworkProvider,
 	Client: ProvideRuntimeApi<Block> + Send + Sync + 'static + HeaderBackend<Block>,
-	<Client as ProvideRuntimeApi<Block>>::Api: AuthorityDiscoveryApi<Block, Error = sp_blockchain::Error>,
+	<Client as ProvideRuntimeApi<Block>>::Api: AuthorityDiscoveryApi<Block>,
 	DhtEventStream: Stream<Item = DhtEvent> + Unpin,
 {
 	new_worker_and_service_with_config(
@@ -121,7 +121,7 @@ where
 	Block: BlockT + Unpin + 'static,
 	Network: NetworkProvider,
 	Client: ProvideRuntimeApi<Block> + Send + Sync + 'static + HeaderBackend<Block>,
-	<Client as ProvideRuntimeApi<Block>>::Api: AuthorityDiscoveryApi<Block, Error = sp_blockchain::Error>,
+	<Client as ProvideRuntimeApi<Block>>::Api: AuthorityDiscoveryApi<Block>,
 	DhtEventStream: Stream<Item = DhtEvent> + Unpin,
 {
 	let (to_worker, from_service) = mpsc::channel(0);

substrate/client/authority-discovery/src/worker.rs

@@ -132,7 +132,7 @@ where
 	Network: NetworkProvider,
 	Client: ProvideRuntimeApi<Block> + Send + Sync + 'static + HeaderBackend<Block>,
 	<Client as ProvideRuntimeApi<Block>>::Api:
-		AuthorityDiscoveryApi<Block, Error = sp_blockchain::Error>,
+		AuthorityDiscoveryApi<Block>,
 	DhtEventStream: Stream<Item = DhtEvent> + Unpin,
 {
 	/// Construct a [`Worker`].
@@ -332,7 +332,7 @@ where
 			.client
 			.runtime_api()
 			.authorities(&id)
-			.map_err(Error::CallingRuntime)?
+			.map_err(|e| Error::CallingRuntime(e.into()))?
 			.into_iter()
 			.filter(|id| !local_keys.contains(id.as_ref()))
 			.collect();
@@ -546,7 +546,7 @@ where
 		let id = BlockId::hash(client.info().best_hash);
 		let authorities = client.runtime_api()
 			.authorities(&id)
-			.map_err(Error::CallingRuntime)?
+			.map_err(|e| Error::CallingRuntime(e.into()))?
 			.into_iter()
 			.map(std::convert::Into::into)
 			.collect::<HashSet<_>>();

substrate/client/authority-discovery/src/worker/tests.rs

@@ -100,8 +100,6 @@ pub(crate) struct RuntimeApi {
 
 sp_api::mock_impl_runtime_apis! {
 	impl AuthorityDiscoveryApi<Block> for RuntimeApi {
-		type Error = sp_blockchain::Error;
-
 		fn authorities(&self) -> Vec<AuthorityId> {
 			self.authorities.clone()
 		}

substrate/client/basic-authorship/src/basic_authorship.rs

@@ -99,7 +99,7 @@ impl<B, Block, C, A> ProposerFactory<A, B, C>
 		C: BlockBuilderProvider<B, Block, C> + HeaderBackend<Block> + ProvideRuntimeApi<Block>
 			+ Send + Sync + 'static,
 		C::Api: ApiExt<Block, StateBackend = backend::StateBackendFor<B, Block>>
-			+ BlockBuilderApi<Block, Error = sp_blockchain::Error>,
+			+ BlockBuilderApi<Block>,
 {
 	pub fn init_with_now(
 		&mut self,
@@ -138,7 +138,7 @@ impl<A, B, Block, C> sp_consensus::Environment<Block> for
 			C: BlockBuilderProvider<B, Block, C> + HeaderBackend<Block> + ProvideRuntimeApi<Block>
 				+ Send + Sync + 'static,
 			C::Api: ApiExt<Block, StateBackend = backend::StateBackendFor<B, Block>>
-				+ BlockBuilderApi<Block, Error = sp_blockchain::Error>,
+				+ BlockBuilderApi<Block>,
 {
 	type CreateProposer = future::Ready<Result<Self::Proposer, Self::Error>>;
 	type Proposer = Proposer<B, Block, C, A>;
@@ -175,7 +175,7 @@ impl<A, B, Block, C> sp_consensus::Proposer<Block> for
 			C: BlockBuilderProvider<B, Block, C> + HeaderBackend<Block> + ProvideRuntimeApi<Block>
 				+ Send + Sync + 'static,
 			C::Api: ApiExt<Block, StateBackend = backend::StateBackendFor<B, Block>>
-				+ BlockBuilderApi<Block, Error = sp_blockchain::Error>,
+				+ BlockBuilderApi<Block>,
 {
 	type Transaction = backend::TransactionFor<B, Block>;
 	type Proposal = Pin<Box<dyn Future<
@@ -221,7 +221,7 @@ impl<A, B, Block, C> Proposer<B, Block, C, A>
 		C: BlockBuilderProvider<B, Block, C> + HeaderBackend<Block> + ProvideRuntimeApi<Block>
 			+ Send + Sync + 'static,
 		C::Api: ApiExt<Block, StateBackend = backend::StateBackendFor<B, Block>>
-			+ BlockBuilderApi<Block, Error = sp_blockchain::Error>,
+			+ BlockBuilderApi<Block>,
 {
 	async fn propose_with(
 		self,

substrate/client/block-builder/src/lib.rs

@@ -35,8 +35,7 @@ use sp_runtime::{
 use sp_blockchain::{ApplyExtrinsicFailed, Error};
 use sp_core::ExecutionContext;
 use sp_api::{
-	Core, ApiExt, ApiErrorFor, ApiRef, ProvideRuntimeApi, StorageChanges, StorageProof,
-	TransactionOutcome,
+	Core, ApiExt, ApiRef, ProvideRuntimeApi, StorageChanges, StorageProof, TransactionOutcome,
 };
 use sp_consensus::RecordProof;
 
@@ -106,8 +105,7 @@ impl<'a, Block, A, B> BlockBuilder<'a, Block, A, B>
 where
 	Block: BlockT,
 	A: ProvideRuntimeApi<Block> + 'a,
-	A::Api: BlockBuilderApi<Block, Error = Error> +
-		ApiExt<Block, StateBackend = backend::StateBackendFor<B, Block>>,
+	A::Api: BlockBuilderApi<Block> + ApiExt<Block, StateBackend = backend::StateBackendFor<B, Block>>,
 	B: backend::Backend<Block>,
 {
 	/// Create a new instance of builder based on the given `parent_hash` and `parent_number`.
@@ -122,7 +120,7 @@ where
 		record_proof: RecordProof,
 		inherent_digests: DigestFor<Block>,
 		backend: &'a B,
-	) -> Result<Self, ApiErrorFor<A, Block>> {
+	) -> Result<Self, Error> {
 		let header = <<Block as BlockT>::Header as HeaderT>::new(
 			parent_number + One::one(),
 			Default::default(),
@@ -155,7 +153,7 @@ where
 	/// Push onto the block's list of extrinsics.
 	///
 	/// This will ensure the extrinsic can be validly executed (by executing it).
-	pub fn push(&mut self, xt: <Block as BlockT>::Extrinsic) -> Result<(), ApiErrorFor<A, Block>> {
+	pub fn push(&mut self, xt: <Block as BlockT>::Extrinsic) -> Result<(), Error> {
 		let block_id = &self.block_id;
 		let extrinsics = &mut self.extrinsics;
 
@@ -174,7 +172,7 @@ where
 						Err(ApplyExtrinsicFailed::Validity(tx_validity).into()),
 					)
 				},
-				Err(e) => TransactionOutcome::Rollback(Err(e)),
+				Err(e) => TransactionOutcome::Rollback(Err(Error::from(e))),
 			}
 		})
 	}
@@ -184,10 +182,7 @@ where
 	/// Returns the build `Block`, the changes to the storage and an optional `StorageProof`
 	/// supplied by `self.api`, combined as [`BuiltBlock`].
 	/// The storage proof will be `Some(_)` when proof recording was enabled.
-	pub fn build(mut self) -> Result<
-		BuiltBlock<Block, backend::StateBackendFor<B, Block>>,
-		ApiErrorFor<A, Block>
-	> {
+	pub fn build(mut self) -> Result<BuiltBlock<Block, backend::StateBackendFor<B, Block>>, Error> {
 		let header = self.api.finalize_block_with_context(
 			&self.block_id, ExecutionContext::BlockConstruction
 		)?;
@@ -227,7 +222,7 @@ where
 	pub fn create_inherents(
 		&mut self,
 		inherent_data: sp_inherents::InherentData,
-	) -> Result<Vec<Block::Extrinsic>, ApiErrorFor<A, Block>> {
+	) -> Result<Vec<Block::Extrinsic>, Error> {
 		let block_id = self.block_id;
 		self.api.execute_in_transaction(move |api| {
 			// `create_inherents` should not change any state, to ensure this we always rollback
@@ -237,7 +232,7 @@ where
 				ExecutionContext::BlockConstruction,
 				inherent_data
 			))
-		})
+		}).map_err(|e| Error::Application(Box::new(e)))
 	}
 }
 

substrate/client/consensus/aura/src/lib.rs

@@ -98,9 +98,9 @@ pub fn slot_duration<A, B, C>(client: &C) -> CResult<SlotDuration> where
 	A: Codec,
 	B: BlockT,
 	C: AuxStore + ProvideRuntimeApi<B>,
-	C::Api: AuraApi<B, A, Error = sp_blockchain::Error>,
+	C::Api: AuraApi<B, A>,
 {
-	SlotDuration::get_or_compute(client, |a, b| a.slot_duration(b))
+	SlotDuration::get_or_compute(client, |a, b| a.slot_duration(b).map_err(Into::into))
 }
 
 /// Get slot author for given block along with authorities.
@@ -515,7 +515,7 @@ impl<C, P, CAW> AuraVerifier<C, P, CAW> where
 		inherent_data: InherentData,
 		timestamp_now: u64,
 	) -> Result<(), Error<B>> where
-		C: ProvideRuntimeApi<B>, C::Api: BlockBuilderApi<B, Error = sp_blockchain::Error>,
+		C: ProvideRuntimeApi<B>, C::Api: BlockBuilderApi<B>,
 		CAW: CanAuthorWith<B>,
 	{
 		const MAX_TIMESTAMP_DRIFT_SECS: u64 = 60;
@@ -534,7 +534,7 @@ impl<C, P, CAW> AuraVerifier<C, P, CAW> where
 			&block_id,
 			block,
 			inherent_data,
-		).map_err(Error::Client)?;
+		).map_err(|e| Error::Client(e.into()))?;
 
 		if !inherent_res.ok() {
 			inherent_res
@@ -578,7 +578,7 @@ impl<B: BlockT, C, P, CAW> Verifier<B> for AuraVerifier<C, P, CAW> where
 		sc_client_api::backend::AuxStore +
 		ProvideCache<B> +
 		BlockOf,
-	C::Api: BlockBuilderApi<B> + AuraApi<B, AuthorityId<P>> + ApiExt<B, Error = sp_blockchain::Error>,
+	C::Api: BlockBuilderApi<B> + AuraApi<B, AuthorityId<P>> + ApiExt<B>,
 	DigestItemFor<B>: CompatibleDigestItem<P>,
 	P: Pair + Send + Sync + 'static,
 	P::Public: Send + Sync + Hash + Eq + Clone + Decode + Encode + Debug + 'static,
@@ -624,7 +624,7 @@ impl<B: BlockT, C, P, CAW> Verifier<B> for AuraVerifier<C, P, CAW> where
 					// skip the inherents verification if the runtime API is old.
 					if self.client
 						.runtime_api()
-						.has_api_with::<dyn BlockBuilderApi<B, Error = ()>, _>(
+						.has_api_with::<dyn BlockBuilderApi<B>, _>(
 							&BlockId::Hash(parent_hash),
 							|v| v >= 2,
 						)
@@ -842,7 +842,7 @@ pub fn import_queue<B, I, C, P, S, CAW>(
 	can_author_with: CAW,
 ) -> Result<DefaultImportQueue<B, C>, sp_consensus::Error> where
 	B: BlockT,
-	C::Api: BlockBuilderApi<B> + AuraApi<B, AuthorityId<P>> + ApiExt<B, Error = sp_blockchain::Error>,
+	C::Api: BlockBuilderApi<B> + AuraApi<B, AuthorityId<P>> + ApiExt<B>,
 	C: 'static + ProvideRuntimeApi<B> + BlockOf + ProvideCache<B> + Send + Sync + AuxStore + HeaderBackend<B>,
 	I: BlockImport<B, Error=ConsensusError, Transaction = sp_api::TransactionFor<C, B>> + Send + Sync + 'static,
 	DigestItemFor<B>: CompatibleDigestItem<P>,

substrate/client/consensus/babe/src/lib.rs

@@ -273,6 +273,8 @@ pub enum Error<B: BlockT> {
 	CheckInherents(String),
 	/// Client error
 	Client(sp_blockchain::Error),
+	/// Runtime Api error.
+	RuntimeApi(sp_api::ApiError),
 	/// Runtime error
 	Runtime(sp_inherents::Error),
 	/// Fork tree error
@@ -310,14 +312,14 @@ impl Config {
 	/// Either fetch the slot duration from disk or compute it from the genesis
 	/// state.
 	pub fn get_or_compute<B: BlockT, C>(client: &C) -> ClientResult<Self> where
-		C: AuxStore + ProvideRuntimeApi<B>, C::Api: BabeApi<B, Error = sp_blockchain::Error>,
+		C: AuxStore + ProvideRuntimeApi<B>, C::Api: BabeApi<B>,
 	{
 		trace!(target: "babe", "Getting slot duration");
 		match sc_consensus_slots::SlotDuration::get_or_compute(client, |a, b| {
-			let has_api_v1 = a.has_api_with::<dyn BabeApi<B, Error = sp_blockchain::Error>, _>(
+			let has_api_v1 = a.has_api_with::<dyn BabeApi<B>, _>(
 				&b, |v| v == 1,
 			)?;
-			let has_api_v2 = a.has_api_with::<dyn BabeApi<B, Error = sp_blockchain::Error>, _>(
+			let has_api_v2 = a.has_api_with::<dyn BabeApi<B>, _>(
 				&b, |v| v == 2,
 			)?;
 
@@ -326,7 +328,7 @@ impl Config {
 					Ok(a.configuration_before_version_2(b)?.into())
 				}
 			} else if has_api_v2 {
-				a.configuration(b)
+				a.configuration(b).map_err(Into::into)
 			} else {
 				Err(sp_blockchain::Error::VersionInvalid(
 					"Unsupported or invalid BabeApi version".to_string()
@@ -846,8 +848,7 @@ impl<Block, Client, SelectChain, CAW> BabeVerifier<Block, Client, SelectChain, C
 where
 	Block: BlockT,
 	Client: AuxStore + HeaderBackend<Block> + HeaderMetadata<Block> + ProvideRuntimeApi<Block>,
-	Client::Api: BlockBuilderApi<Block, Error = sp_blockchain::Error>
-		+ BabeApi<Block, Error = sp_blockchain::Error>,
+	Client::Api: BlockBuilderApi<Block> + BabeApi<Block>,
 	SelectChain: sp_consensus::SelectChain<Block>,
 	CAW: CanAuthorWith<Block>,
 {
@@ -871,7 +872,7 @@ where
 			&block_id,
 			block,
 			inherent_data,
-		).map_err(Error::Client)?;
+		).map_err(Error::RuntimeApi)?;
 
 		if !inherent_res.ok() {
 			inherent_res
@@ -934,7 +935,7 @@ where
 			self.client
 				.runtime_api()
 				.generate_key_ownership_proof(block_id, slot, equivocation_proof.offender.clone())
-				.map_err(Error::Client)
+				.map_err(Error::RuntimeApi)
 		};
 
 		let parent_id = BlockId::Hash(*header.parent_hash());
@@ -957,7 +958,7 @@ where
 				equivocation_proof,
 				key_owner_proof,
 			)
-			.map_err(Error::Client)?;
+			.map_err(Error::RuntimeApi)?;
 
 		info!(target: "babe", "Submitted equivocation report for author {:?}", author);
 
@@ -971,7 +972,7 @@ where
 	Block: BlockT,
 	Client: HeaderMetadata<Block, Error = sp_blockchain::Error> + HeaderBackend<Block> + ProvideRuntimeApi<Block>
 		+ Send + Sync + AuxStore + ProvideCache<Block>,
-	Client::Api: BlockBuilderApi<Block, Error = sp_blockchain::Error> + BabeApi<Block, Error = sp_blockchain::Error>,
+	Client::Api: BlockBuilderApi<Block> + BabeApi<Block>,
 	SelectChain: sp_consensus::SelectChain<Block>,
 	CAW: CanAuthorWith<Block> + Send + Sync,
 {
@@ -1498,7 +1499,7 @@ pub fn import_queue<Block: BlockT, Client, SelectChain, Inner, CAW>(
 		+ Send + Sync + 'static,
 	Client: ProvideRuntimeApi<Block> + ProvideCache<Block> + Send + Sync + AuxStore + 'static,
 	Client: HeaderBackend<Block> + HeaderMetadata<Block, Error = sp_blockchain::Error>,
-	Client::Api: BlockBuilderApi<Block> + BabeApi<Block> + ApiExt<Block, Error = sp_blockchain::Error>,
+	Client::Api: BlockBuilderApi<Block> + BabeApi<Block> + ApiExt<Block>,
 	SelectChain: sp_consensus::SelectChain<Block> + 'static,
 	CAW: CanAuthorWith<Block> + Send + Sync + 'static,
 {

substrate/client/consensus/manual-seal/src/consensus/babe.rs

@@ -73,7 +73,7 @@ impl<B, C> BabeConsensusDataProvider<B, C>
 	where
 		B: BlockT,
 		C: AuxStore + HeaderBackend<B> + ProvideRuntimeApi<B> + HeaderMetadata<B, Error = sp_blockchain::Error>,
-		C::Api: BabeApi<B, Error = sp_blockchain::Error>,
+		C::Api: BabeApi<B>,
 {
 	pub fn new(
 		client: Arc<C>,
@@ -131,7 +131,7 @@ impl<B, C> ConsensusDataProvider<B> for BabeConsensusDataProvider<B, C>
 	where
 		B: BlockT,
 		C: AuxStore + HeaderBackend<B> + HeaderMetadata<B, Error = sp_blockchain::Error> + ProvideRuntimeApi<B>,
-		C::Api: BabeApi<B, Error = sp_blockchain::Error>,
+		C::Api: BabeApi<B>,
 {
 	type Transaction = TransactionFor<C, B>;
 
@@ -259,7 +259,7 @@ impl SlotTimestampProvider {
 		where
 			B: BlockT,
 			C: AuxStore + HeaderBackend<B> + ProvideRuntimeApi<B>,
-			C::Api: BabeApi<B, Error = sp_blockchain::Error>,
+			C::Api: BabeApi<B>,
 	{
 		let slot_duration = Config::get_or_compute(&*client)?.slot_duration;
 		let info = client.info();

substrate/client/consensus/pow/src/lib.rs

@@ -232,7 +232,7 @@ impl<B, I, C, S, Algorithm, CAW> PowBlockImport<B, I, C, S, Algorithm, CAW> wher
 	I: BlockImport<B, Transaction = sp_api::TransactionFor<C, B>> + Send + Sync,
 	I::Error: Into<ConsensusError>,
 	C: ProvideRuntimeApi<B> + Send + Sync + HeaderBackend<B> + AuxStore + ProvideCache<B> + BlockOf,
-	C::Api: BlockBuilderApi<B, Error = sp_blockchain::Error>,
+	C::Api: BlockBuilderApi<B>,
 	Algorithm: PowAlgorithm<B>,
 	CAW: CanAuthorWith<B>,
 {
@@ -284,7 +284,7 @@ impl<B, I, C, S, Algorithm, CAW> PowBlockImport<B, I, C, S, Algorithm, CAW> wher
 			&block_id,
 			block,
 			inherent_data,
-		).map_err(Error::Client)?;
+		).map_err(|e| Error::Client(e.into()))?;
 
 		if !inherent_res.ok() {
 			inherent_res
@@ -314,7 +314,7 @@ impl<B, I, C, S, Algorithm, CAW> BlockImport<B> for PowBlockImport<B, I, C, S, A
 	I::Error: Into<ConsensusError>,
 	S: SelectChain<B>,
 	C: ProvideRuntimeApi<B> + Send + Sync + HeaderBackend<B> + AuxStore + ProvideCache<B> + BlockOf,
-	C::Api: BlockBuilderApi<B, Error = sp_blockchain::Error>,
+	C::Api: BlockBuilderApi<B>,
 	Algorithm: PowAlgorithm<B>,
 	Algorithm::Difficulty: 'static,
 	CAW: CanAuthorWith<B>,

substrate/client/executor/common/src/error.rs

@@ -37,8 +37,8 @@ pub enum Error {
 	#[error(transparent)]
 	Wasmi(#[from] wasmi::Error),
 
-	#[error("API Error: {0}")]
-	ApiError(String),
+	#[error("Error calling api function: {0}")]
+	ApiError(Box<dyn std::error::Error + Send + Sync>),
 
 	#[error("Method not found: '{0}'")]
 	MethodNotFound(String),
@@ -96,16 +96,16 @@ pub enum Error {
 
 	#[error(transparent)]
 	RuntimeConstruction(#[from] WasmError),
-	
+
 	#[error("Shared memory is not supported")]
 	SharedMemUnsupported,
-	
+
 	#[error("Imported globals are not supported yet")]
 	ImportedGlobalsUnsupported,
-	
+
 	#[error("initializer expression can have only up to 2 expressions in wasm 1.0")]
 	InitializerHasTooManyExpressions,
-	
+
 	#[error("Invalid initializer expression provided {0}")]
 	InvalidInitializerExpression(String),
 }

substrate/client/executor/src/native_executor.rs

@@ -456,7 +456,7 @@ impl<D: NativeExecutionDispatch + 'static> CodeExecutor for NativeExecutor<D> {
 
 	fn call<
 		R: Decode + Encode + PartialEq,
-		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+		NC: FnOnce() -> result::Result<R, Box<dyn std::error::Error + Send + Sync>> + UnwindSafe,
 	>(
 		&self,
 		ext: &mut dyn Externalities,
@@ -514,7 +514,7 @@ impl<D: NativeExecutionDispatch + 'static> CodeExecutor for NativeExecutor<D> {
 						let res = with_externalities_safe(&mut **ext, move || (call)())
 							.and_then(|r| r
 								.map(NativeOrEncoded::Native)
-								.map_err(|s| Error::ApiError(s))
+								.map_err(Error::ApiError)
 							);
 
 						Ok(res)

substrate/client/executor/src/wasm_runtime.rs

@@ -414,7 +414,7 @@ mod tests {
 			authoring_version: 1,
 			spec_version: 1,
 			impl_version: 1,
-			apis: sp_api::create_apis_vec!([(Core::<Block, Error = ()>::ID, 1)]),
+			apis: sp_api::create_apis_vec!([(Core::<Block>::ID, 1)]),
 		};
 
 		let version = decode_version(&old_runtime_version.encode()).unwrap();
@@ -429,7 +429,7 @@ mod tests {
 			authoring_version: 1,
 			spec_version: 1,
 			impl_version: 1,
-			apis: sp_api::create_apis_vec!([(Core::<Block, Error = ()>::ID, 3)]),
+			apis: sp_api::create_apis_vec!([(Core::<Block>::ID, 3)]),
 		};
 
 		decode_version(&old_runtime_version.encode()).unwrap_err();
@@ -443,7 +443,7 @@ mod tests {
 			authoring_version: 1,
 			spec_version: 1,
 			impl_version: 1,
-			apis: sp_api::create_apis_vec!([(Core::<Block, Error = ()>::ID, 3)]),
+			apis: sp_api::create_apis_vec!([(Core::<Block>::ID, 3)]),
 			transaction_version: 3,
 		};
 

substrate/client/finality-grandpa/Cargo.toml

@@ -59,4 +59,3 @@ sp-state-machine = { version = "0.9.0", path = "../../primitives/state-machine"
 sp-tracing = { version = "3.0.0", path = "../../primitives/tracing" }
 tokio = { version = "0.2", features = ["rt-core"] }
 tempfile = "3.1.0"
-sp-api = { version = "3.0.0", path = "../../primitives/api" }

substrate/client/finality-grandpa/src/environment.rs

@@ -480,7 +480,7 @@ where
 	Block: BlockT,
 	BE: Backend<Block>,
 	C: crate::ClientForGrandpa<Block, BE>,
-	C::Api: GrandpaApi<Block, Error = sp_blockchain::Error>,
+	C::Api: GrandpaApi<Block>,
 	N: NetworkT<Block>,
 	SC: SelectChain<Block> + 'static,
 {
@@ -549,7 +549,7 @@ where
 				authority_set.set_id,
 				equivocation.offender().clone(),
 			)
-			.map_err(Error::Client)?
+			.map_err(Error::RuntimeApi)?
 		{
 			Some(proof) => proof,
 			None => {
@@ -571,7 +571,7 @@ where
 				equivocation_proof,
 				key_owner_proof,
 			)
-			.map_err(Error::Client)?;
+			.map_err(Error::RuntimeApi)?;
 
 		Ok(())
 	}
@@ -726,7 +726,7 @@ where
 	Block: 'static,
 	B: Backend<Block>,
 	C: crate::ClientForGrandpa<Block, B> + 'static,
-	C::Api: GrandpaApi<Block, Error = sp_blockchain::Error>,
+	C::Api: GrandpaApi<Block>,
 	N: NetworkT<Block> + 'static + Send + Sync,
 	SC: SelectChain<Block> + 'static,
 	VR: VotingRule<Block, C>,

substrate/client/finality-grandpa/src/import.rs

@@ -663,6 +663,7 @@ where
 					Error::Safety(error) => ConsensusError::ClientImport(error),
 					Error::Signing(error) => ConsensusError::ClientImport(error),
 					Error::Timer(error) => ConsensusError::ClientImport(error.to_string()),
+					Error::RuntimeApi(error) => ConsensusError::ClientImport(error.to_string()),
 				});
 			},
 			Ok(_) => {

substrate/client/finality-grandpa/src/lib.rs

@@ -295,6 +295,8 @@ pub enum Error {
 	Safety(String),
 	/// A timer failed to fire.
 	Timer(io::Error),
+	/// A runtime api request failed.
+	RuntimeApi(sp_api::ApiError),
 }
 
 impl From<GrandpaError> for Error {
@@ -698,7 +700,7 @@ where
 	NumberFor<Block>: BlockNumberOps,
 	DigestFor<Block>: Encode,
 	C: ClientForGrandpa<Block, BE> + 'static,
-	C::Api: GrandpaApi<Block, Error = sp_blockchain::Error>,
+	C::Api: GrandpaApi<Block>,
 {
 	let GrandpaParams {
 		mut config,
@@ -824,7 +826,7 @@ where
 	Block: BlockT,
 	B: Backend<Block> + 'static,
 	C: ClientForGrandpa<Block, B> + 'static,
-	C::Api: GrandpaApi<Block, Error = sp_blockchain::Error>,
+	C::Api: GrandpaApi<Block>,
 	N: NetworkT<Block> + Sync,
 	NumberFor<Block>: BlockNumberOps,
 	SC: SelectChain<Block> + 'static,
@@ -1042,7 +1044,7 @@ where
 	NumberFor<Block>: BlockNumberOps,
 	SC: SelectChain<Block> + 'static,
 	C: ClientForGrandpa<Block, B> + 'static,
-	C::Api: GrandpaApi<Block, Error = sp_blockchain::Error>,
+	C::Api: GrandpaApi<Block>,
 	VR: VotingRule<Block, C> + Clone + 'static,
 {
 	type Output = Result<(), Error>;

substrate/client/finality-grandpa/src/tests.rs

@@ -174,8 +174,6 @@ impl ProvideRuntimeApi<Block> for TestApi {
 
 sp_api::mock_impl_runtime_apis! {
 	impl GrandpaApi<Block> for RuntimeApi {
-		type Error = sp_blockchain::Error;
-
 		fn grandpa_authorities(&self) -> AuthorityList {
 			self.inner.genesis_authorities.clone()
 		}

substrate/client/light/src/call_executor.rs

@@ -104,7 +104,7 @@ impl<Block, B, Local> CallExecutor<Block> for
 			Result<NativeOrEncoded<R>, Self::Error>
 		) -> Result<NativeOrEncoded<R>, Self::Error>,
 		R: Encode + Decode + PartialEq,
-		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+		NC: FnOnce() -> result::Result<R, sp_api::ApiError> + UnwindSafe,
 	>(
 		&self,
 		initialize_block_fn: IB,

substrate/client/offchain/src/lib.rs

@@ -132,10 +132,10 @@ impl<Client, Storage, Block> OffchainWorkers<
 	) -> impl Future<Output = ()> {
 		let runtime = self.client.runtime_api();
 		let at = BlockId::hash(header.hash());
-		let has_api_v1 = runtime.has_api_with::<dyn OffchainWorkerApi<Block, Error = ()>, _>(
+		let has_api_v1 = runtime.has_api_with::<dyn OffchainWorkerApi<Block>, _>(
 			&at, |v| v == 1
 		);
-		let has_api_v2 = runtime.has_api_with::<dyn OffchainWorkerApi<Block, Error = ()>, _>(
+		let has_api_v2 = runtime.has_api_with::<dyn OffchainWorkerApi<Block>, _>(
 			&at, |v| v == 2
 		);
 		let version = match (has_api_v1, has_api_v2) {

substrate/client/rpc/src/author/mod.rs

@@ -24,12 +24,9 @@ mod tests;
 use std::{sync::Arc, convert::TryInto};
 use log::warn;
 
-use sp_blockchain::{Error as ClientError, HeaderBackend};
+use sp_blockchain::HeaderBackend;
 
-use rpc::futures::{
-	Sink, Future,
-	future::result,
-};
+use rpc::futures::{Sink, Future, future::result};
 use futures::{StreamExt as _, compat::Compat};
 use futures::future::{ready, FutureExt, TryFutureExt};
 use sc_rpc_api::DenyUnsafe;
@@ -93,7 +90,7 @@ impl<P, Client> AuthorApi<TxHash<P>, BlockHash<P>> for Author<P, Client>
 	where
 		P: TransactionPool + Sync + Send + 'static,
 		Client: HeaderBackend<P::Block> + ProvideRuntimeApi<P::Block> + Send + Sync + 'static,
-		Client::Api: SessionKeys<P::Block, Error = ClientError>,
+		Client::Api: SessionKeys<P::Block>,
 {
 	type Metadata = crate::Metadata;
 

substrate/client/rpc/src/state/mod.rs

@@ -178,9 +178,8 @@ pub fn new_full<BE, Block: BlockT, Client>(
 		BE: Backend<Block> + 'static,
 		Client: ExecutorProvider<Block> + StorageProvider<Block, BE> + ProofProvider<Block> + HeaderBackend<Block>
 			+ HeaderMetadata<Block, Error = sp_blockchain::Error> + BlockchainEvents<Block>
-			+ CallApiAt<Block, Error = sp_blockchain::Error>
-			+ ProvideRuntimeApi<Block> + Send + Sync + 'static,
-		Client::Api: Metadata<Block, Error = sp_blockchain::Error>,
+			+ CallApiAt<Block> + ProvideRuntimeApi<Block> + Send + Sync + 'static,
+		Client::Api: Metadata<Block>,
 {
 	let child_backend = Box::new(
 		self::state_full::FullState::new(client.clone(), subscriptions.clone())

substrate/client/rpc/src/state/state_full.rs

@@ -223,9 +223,9 @@ impl<BE, Block, Client> StateBackend<Block, Client> for FullState<BE, Block, Cli
 	BE: Backend<Block> + 'static,
 	Client: ExecutorProvider<Block> + StorageProvider<Block, BE> + ProofProvider<Block> + HeaderBackend<Block>
 		+ HeaderMetadata<Block, Error = sp_blockchain::Error> + BlockchainEvents<Block>
-		+ CallApiAt<Block, Error = sp_blockchain::Error> + ProvideRuntimeApi<Block>
+		+ CallApiAt<Block> + ProvideRuntimeApi<Block>
 		+ Send + Sync + 'static,
-	Client::Api: Metadata<Block, Error = sp_blockchain::Error>,
+	Client::Api: Metadata<Block>,
 {
 	fn call(
 		&self,
@@ -344,17 +344,23 @@ impl<BE, Block, Client> StateBackend<Block, Client> for FullState<BE, Block, Cli
 	fn metadata(&self, block: Option<Block::Hash>) -> FutureResult<Bytes> {
 		Box::new(result(
 			self.block_or_best(block)
+				.map_err(client_err)
 				.and_then(|block|
-					self.client.runtime_api().metadata(&BlockId::Hash(block)).map(Into::into)
-				)
-				.map_err(client_err)))
+					self.client.runtime_api().metadata(&BlockId::Hash(block))
+						.map(Into::into)
+						.map_err(|e| Error::Client(Box::new(e))))
+		))
 	}
 
 	fn runtime_version(&self, block: Option<Block::Hash>) -> FutureResult<RuntimeVersion> {
 		Box::new(result(
 			self.block_or_best(block)
-				.and_then(|block| self.client.runtime_version_at(&BlockId::Hash(block)))
-				.map_err(client_err)))
+				.map_err(client_err)
+				.and_then(|block|
+					self.client.runtime_version_at(&BlockId::Hash(block))
+						.map_err(|e| Error::Client(Box::new(e)))
+				)
+		))
 	}
 
 	fn query_storage(
@@ -432,7 +438,7 @@ impl<BE, Block, Client> StateBackend<Block, Client> for FullState<BE, Block, Cli
 					let info = client.info();
 					let version = client
 						.runtime_version_at(&BlockId::hash(info.best_hash))
-						.map_err(client_err)
+						.map_err(|e| Error::Client(Box::new(e)))
 						.map_err(Into::into);
 					if previous_version != version {
 						previous_version = version.clone();
@@ -528,9 +534,9 @@ impl<BE, Block, Client> ChildStateBackend<Block, Client> for FullState<BE, Block
 	BE: Backend<Block> + 'static,
 	Client: ExecutorProvider<Block> + StorageProvider<Block, BE> + HeaderBackend<Block>
 		+ HeaderMetadata<Block, Error = sp_blockchain::Error> + BlockchainEvents<Block>
-		+ CallApiAt<Block, Error = sp_blockchain::Error> + ProvideRuntimeApi<Block>
+		+ CallApiAt<Block> + ProvideRuntimeApi<Block>
 		+ Send + Sync + 'static,
-	Client::Api: Metadata<Block, Error = sp_blockchain::Error>,
+	Client::Api: Metadata<Block>,
 {
 	fn storage_keys(
 		&self,

substrate/client/service/src/builder.rs

@@ -542,14 +542,13 @@ pub fn spawn_tasks<TBl, TBackend, TExPool, TRpc, TCl>(
 		TCl: ProvideRuntimeApi<TBl> + HeaderMetadata<TBl, Error=sp_blockchain::Error> + Chain<TBl> +
 		BlockBackend<TBl> + BlockIdTo<TBl, Error=sp_blockchain::Error> + ProofProvider<TBl> +
 		HeaderBackend<TBl> + BlockchainEvents<TBl> + ExecutorProvider<TBl> + UsageProvider<TBl> +
-		StorageProvider<TBl, TBackend> + CallApiAt<TBl, Error=sp_blockchain::Error> +
+		StorageProvider<TBl, TBackend> + CallApiAt<TBl> +
 		Send + 'static,
 		<TCl as ProvideRuntimeApi<TBl>>::Api:
 			sp_api::Metadata<TBl> +
 			sc_offchain::OffchainWorkerApi<TBl> +
 			sp_transaction_pool::runtime_api::TaggedTransactionQueue<TBl> +
 			sp_session::SessionKeys<TBl> +
-			sp_api::ApiErrorExt<Error = sp_blockchain::Error> +
 			sp_api::ApiExt<TBl, StateBackend = TBackend::State>,
 		TBl: BlockT,
 		TBackend: 'static + sc_client_api::backend::Backend<TBl> + Send,
@@ -578,7 +577,7 @@ pub fn spawn_tasks<TBl, TBackend, TExPool, TRpc, TCl>(
 		client.clone(),
 		&BlockId::Hash(chain_info.best_hash),
 		config.dev_key_seed.clone().map(|s| vec![s]).unwrap_or_default(),
-	)?;
+	).map_err(|e| Error::Application(Box::new(e)))?;
 
 	let telemetry_connection_notifier = init_telemetry(
 		&mut config,
@@ -729,14 +728,14 @@ fn gen_handler<TBl, TBackend, TExPool, TRpc, TCl>(
 		TBl: BlockT,
 		TCl: ProvideRuntimeApi<TBl> + BlockchainEvents<TBl> + HeaderBackend<TBl> +
 		HeaderMetadata<TBl, Error=sp_blockchain::Error> + ExecutorProvider<TBl> +
-		CallApiAt<TBl, Error=sp_blockchain::Error> + ProofProvider<TBl> +
+		CallApiAt<TBl> + ProofProvider<TBl> +
 		StorageProvider<TBl, TBackend> + BlockBackend<TBl> + Send + Sync + 'static,
 		TExPool: MaintainedTransactionPool<Block=TBl, Hash = <TBl as BlockT>::Hash> + 'static,
 		TBackend: sc_client_api::backend::Backend<TBl> + 'static,
 		TRpc: sc_rpc::RpcExtension<sc_rpc::Metadata>,
 		<TCl as ProvideRuntimeApi<TBl>>::Api:
 			sp_session::SessionKeys<TBl> +
-			sp_api::Metadata<TBl, Error = sp_blockchain::Error>,
+			sp_api::Metadata<TBl>,
 {
 	use sc_rpc::{chain, state, author, system, offchain};
 

substrate/client/service/src/client/call_executor.rs

@@ -161,7 +161,7 @@ where
 			Result<NativeOrEncoded<R>, Self::Error>
 		) -> Result<NativeOrEncoded<R>, Self::Error>,
 		R: Encode + Decode + PartialEq,
-		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+		NC: FnOnce() -> result::Result<R, sp_api::ApiError> + UnwindSafe,
 	>(
 		&self,
 		initialize_block_fn: IB,
@@ -226,7 +226,10 @@ where
 				);
 				// TODO: https://github.com/paritytech/substrate/issues/4455
 				// .with_storage_transaction_cache(storage_transaction_cache.as_mut().map(|c| &mut **c))
-				state_machine.execute_using_consensus_failure_handler(execution_manager, native_call)
+				state_machine.execute_using_consensus_failure_handler(
+					execution_manager,
+					native_call.map(|n| || (n)().map_err(|e| Box::new(e) as Box<_>)),
+				)
 			},
 			None => {
 				let state_runtime_code = sp_state_machine::backend::BackendRuntimeCode::new(&state);
@@ -245,7 +248,10 @@ where
 					&runtime_code,
 					self.spawn_handle.clone(),
 				).with_storage_transaction_cache(storage_transaction_cache.as_mut().map(|c| &mut **c));
-				state_machine.execute_using_consensus_failure_handler(execution_manager, native_call)
+				state_machine.execute_using_consensus_failure_handler(
+					execution_manager,
+					native_call.map(|n| || (n)().map_err(|e| Box::new(e) as Box<_>)),
+				)
 			}
 		}.map_err(Into::into)
 	}

substrate/client/service/src/client/client.rs

@@ -604,7 +604,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		new_cache: HashMap<CacheKeyId, Vec<u8>>,
 	) -> sp_blockchain::Result<ImportResult> where
 		Self: ProvideRuntimeApi<Block>,
-		<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block, Error = Error> +
+		<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block> +
 			ApiExt<Block, StateBackend = B::State>,
 	{
 		let BlockImportParams {
@@ -696,7 +696,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		import_existing: bool,
 	) -> sp_blockchain::Result<ImportResult> where
 		Self: ProvideRuntimeApi<Block>,
-		<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block, Error = Error> +
+		<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block> +
 				ApiExt<Block, StateBackend = B::State>,
 	{
 		let parent_hash = import_headers.post().parent_hash().clone();
@@ -838,7 +838,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 	) -> sp_blockchain::Result<Option<ImportResult>>
 		where
 			Self: ProvideRuntimeApi<Block>,
-			<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block, Error = Error> +
+			<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block> +
 				ApiExt<Block, StateBackend = B::State>,
 	{
 		let parent_hash = import_block.header.parent_hash();
@@ -1272,7 +1272,7 @@ impl<B, E, Block, RA> BlockBuilderProvider<B, Block, Self> for Client<B, E, Bloc
 		Block: BlockT,
 		Self: ChainHeaderBackend<Block> + ProvideRuntimeApi<Block>,
 		<Self as ProvideRuntimeApi<Block>>::Api: ApiExt<Block, StateBackend = backend::StateBackendFor<B, Block>>
-			+ BlockBuilderApi<Block, Error = Error>,
+			+ BlockBuilderApi<Block>,
 {
 	fn new_block_at<R: Into<RecordProof>>(
 		&self,
@@ -1628,18 +1628,17 @@ impl<B, E, Block, RA> CallApiAt<Block> for Client<B, E, Block, RA> where
 	E: CallExecutor<Block, Backend = B> + Send + Sync,
 	Block: BlockT,
 {
-	type Error = Error;
 	type StateBackend = B::State;
 
 	fn call_api_at<
 		'a,
 		R: Encode + Decode + PartialEq,
-		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
-		C: CoreApi<Block, Error = Error>,
+		NC: FnOnce() -> result::Result<R, sp_api::ApiError> + UnwindSafe,
+		C: CoreApi<Block>,
 	>(
 		&self,
 		params: CallApiAtParams<'a, Block, C, NC, B::State>,
-	) -> sp_blockchain::Result<NativeOrEncoded<R>> {
+	) -> Result<NativeOrEncoded<R>, sp_api::ApiError> {
 		let core_api = params.core_api;
 		let at = params.at;
 
@@ -1649,7 +1648,9 @@ impl<B, E, Block, RA> CallApiAt<Block> for Client<B, E, Block, RA> where
 		);
 
 		self.executor.contextual_call::<_, fn(_,_) -> _,_,_>(
-			|| core_api.initialize_block(at, &self.prepare_environment_block(at)?),
+			|| core_api
+				.initialize_block(at, &self.prepare_environment_block(at)?)
+				.map_err(Error::RuntimeApiError),
 			at,
 			params.function,
 			&params.arguments,
@@ -1660,11 +1661,14 @@ impl<B, E, Block, RA> CallApiAt<Block> for Client<B, E, Block, RA> where
 			params.native_call,
 			params.recorder,
 			Some(extensions),
-		)
+		).map_err(Into::into)
 	}
 
-	fn runtime_version_at(&self, at: &BlockId<Block>) -> sp_blockchain::Result<RuntimeVersion> {
-		self.runtime_version_at(at)
+	fn runtime_version_at(
+		&self,
+		at: &BlockId<Block>,
+	) -> Result<RuntimeVersion, sp_api::ApiError> {
+		self.runtime_version_at(at).map_err(Into::into)
 	}
 }
 
@@ -1676,7 +1680,7 @@ impl<B, E, Block, RA> sp_consensus::BlockImport<Block> for &Client<B, E, Block,
 	E: CallExecutor<Block> + Send + Sync,
 	Block: BlockT,
 	Client<B, E, Block, RA>: ProvideRuntimeApi<Block>,
-	<Client<B, E, Block, RA> as ProvideRuntimeApi<Block>>::Api: CoreApi<Block, Error = Error> +
+	<Client<B, E, Block, RA> as ProvideRuntimeApi<Block>>::Api: CoreApi<Block> +
 		ApiExt<Block, StateBackend = B::State>,
 {
 	type Error = ConsensusError;
@@ -1776,7 +1780,7 @@ impl<B, E, Block, RA> sp_consensus::BlockImport<Block> for Client<B, E, Block, R
 	E: CallExecutor<Block> + Send + Sync,
 	Block: BlockT,
 	Self: ProvideRuntimeApi<Block>,
-	<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block, Error = Error> +
+	<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block> +
 		ApiExt<Block, StateBackend = B::State>,
 {
 	type Error = ConsensusError;
@@ -1935,7 +1939,7 @@ impl<B, E, Block, RA> backend::AuxStore for Client<B, E, Block, RA>
 		E: CallExecutor<Block>,
 		Block: BlockT,
 		Self: ProvideRuntimeApi<Block>,
-		<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block, Error = Error>,
+		<Self as ProvideRuntimeApi<Block>>::Api: CoreApi<Block>,
 {
 	/// Insert auxiliary data into key-value store.
 	fn insert_aux<
@@ -1965,7 +1969,7 @@ impl<B, E, Block, RA> backend::AuxStore for &Client<B, E, Block, RA>
 		E: CallExecutor<Block>,
 		Block: BlockT,
 		Client<B, E, Block, RA>: ProvideRuntimeApi<Block>,
-		<Client<B, E, Block, RA> as ProvideRuntimeApi<Block>>::Api: CoreApi<Block, Error = Error>,
+		<Client<B, E, Block, RA> as ProvideRuntimeApi<Block>>::Api: CoreApi<Block>,
 {
 	fn insert_aux<
 		'a,

substrate/client/service/src/error.rs

@@ -33,13 +33,13 @@ pub type Result<T> = std::result::Result<T, Error>;
 pub enum Error {
 	#[error(transparent)]
 	Client(#[from] sp_blockchain::Error),
-	
+
 	#[error(transparent)]
 	Io(#[from] std::io::Error),
-	
+
 	#[error(transparent)]
 	Consensus(#[from] sp_consensus::Error),
-	
+
 	#[error(transparent)]
 	Network(#[from] sc_network::error::Error),
 

substrate/client/service/test/src/client/light.rs

@@ -215,7 +215,7 @@ impl CallExecutor<Block> for DummyCallExecutor {
 			Result<NativeOrEncoded<R>, Self::Error>
 		) -> Result<NativeOrEncoded<R>, Self::Error>,
 		R: Encode + Decode + PartialEq,
-		NC: FnOnce() -> Result<R, String> + UnwindSafe,
+		NC: FnOnce() -> Result<R, sp_api::ApiError> + UnwindSafe,
 	>(
 		&self,
 		_initialize_block_fn: IB,

substrate/client/service/test/src/client/mod.rs

@@ -1327,7 +1327,9 @@ fn doesnt_import_blocks_that_revert_finality() {
 
 	let import_err = client.import(BlockOrigin::Own, b3).err().unwrap();
 	let expected_err = ConsensusError::ClientImport(
-		sp_blockchain::Error::NotInFinalizedChain.to_string()
+		sp_blockchain::Error::RuntimeApiError(
+			sp_api::ApiError::Application(Box::new(sp_blockchain::Error::NotInFinalizedChain))
+		).to_string()
 	);
 
 	assert_eq!(

substrate/client/transaction-pool/src/api.rs

@@ -84,7 +84,6 @@ where
 	Client: ProvideRuntimeApi<Block> + BlockBackend<Block> + BlockIdTo<Block>,
 	Client: Send + Sync + 'static,
 	Client::Api: TaggedTransactionQueue<Block>,
-	sp_api::ApiErrorFor<Client, Block>: Send + std::fmt::Display,
 {
 	type Block = Block;
 	type Error = error::Error;
@@ -166,14 +165,13 @@ where
 	Client: ProvideRuntimeApi<Block> + BlockBackend<Block> + BlockIdTo<Block>,
 	Client: Send + Sync + 'static,
 	Client::Api: TaggedTransactionQueue<Block>,
-	sp_api::ApiErrorFor<Client, Block>: Send + std::fmt::Display,
 {
 	sp_tracing::within_span!(sp_tracing::Level::TRACE, "validate_transaction";
 	{
 		let runtime_api = client.runtime_api();
 		let has_v2 = sp_tracing::within_span! { sp_tracing::Level::TRACE, "check_version";
 			runtime_api
-				.has_api_with::<dyn TaggedTransactionQueue<Block, Error=()>, _>(&at, |v| v >= 2)
+				.has_api_with::<dyn TaggedTransactionQueue<Block>, _>(&at, |v| v >= 2)
 				.unwrap_or_default()
 		};
 
@@ -198,7 +196,6 @@ where
 	Client: ProvideRuntimeApi<Block> + BlockBackend<Block> + BlockIdTo<Block>,
 	Client: Send + Sync + 'static,
 	Client::Api: TaggedTransactionQueue<Block>,
-	sp_api::ApiErrorFor<Client, Block>: Send + std::fmt::Display,
 {
 	/// Validates a transaction by calling into the runtime, same as
 	/// `validate_transaction` but blocks the current thread when performing

substrate/client/transaction-pool/src/lib.rs

@@ -360,7 +360,6 @@ where
 		+ sp_runtime::traits::BlockIdTo<Block>,
 	Client: sc_client_api::ExecutorProvider<Block> + Send + Sync + 'static,
 	Client::Api: sp_transaction_pool::runtime_api::TaggedTransactionQueue<Block>,
-	sp_api::ApiErrorFor<Client, Block>: Send + std::fmt::Display,
 {
 	/// Create new basic transaction pool for a full node with the provided api.
 	pub fn new_full(
@@ -391,7 +390,6 @@ where
 		+ sp_runtime::traits::BlockIdTo<Block>,
 	Client: Send + Sync + 'static,
 	Client::Api: sp_transaction_pool::runtime_api::TaggedTransactionQueue<Block>,
-	sp_api::ApiErrorFor<Client, Block>: Send + std::fmt::Display,
 {
 	type Block = Block;
 	type Hash = sc_transaction_graph::ExtrinsicHash<FullChainApi<Client, Block>>;

substrate/primitives/api/proc-macro/src/decl_runtime_apis.rs

@@ -187,14 +187,15 @@ fn generate_native_call_generators(decl: &ItemTrait) -> Result<TokenStream> {
 	result.push(quote!(
 		#[cfg(any(feature = "std", test))]
 		fn convert_between_block_types
-			<I: #crate_::Encode, R: #crate_::Decode>(
-				input: &I, error_desc: &'static str,
-			) -> std::result::Result<R, String>
+			<I: #crate_::Encode, R: #crate_::Decode, F: FnOnce(#crate_::codec::Error) -> #crate_::ApiError>(
+				input: &I,
+				map_error: F,
+			) -> std::result::Result<R, #crate_::ApiError>
 		{
 			<R as #crate_::DecodeLimit>::decode_with_depth_limit(
 				#crate_::MAX_EXTRINSIC_DEPTH,
 				&mut &#crate_::Encode::encode(input)[..],
-			).map_err(|e| format!("{} {}", error_desc, e))
+			).map_err(map_error)
 		}
 	));
 
@@ -202,19 +203,26 @@ fn generate_native_call_generators(decl: &ItemTrait) -> Result<TokenStream> {
 	for fn_ in fns {
 		let params = extract_parameter_names_types_and_borrows(&fn_, AllowSelfRefInParameters::No)?;
 		let trait_fn_name = &fn_.ident;
+		let function_name_str = fn_.ident.to_string();
 		let fn_name = generate_native_call_generator_fn_name(&fn_.ident);
 		let output = return_type_replace_block_with_node_block(fn_.output.clone());
 		let output_ty = return_type_extract_type(&output);
-		let output = quote!( std::result::Result<#output_ty, String> );
+		let output = quote!( std::result::Result<#output_ty, #crate_::ApiError> );
 
 		// Every type that is using the `Block` generic parameter, we need to encode/decode,
 		// to make it compatible between the runtime/node.
 		let conversions = params.iter().filter(|v| type_is_using_block(&v.1)).map(|(n, t, _)| {
-			let name_str = format!(
-				"Could not convert parameter `{}` between node and runtime:", quote!(#n)
-			);
+			let param_name = quote!(#n).to_string();
+
 			quote!(
-				let #n: #t = convert_between_block_types(&#n, #name_str)?;
+				let #n: #t = convert_between_block_types(
+					&#n,
+					|e| #crate_::ApiError::FailedToConvertParameter {
+						function: #function_name_str,
+						parameter: #param_name,
+						error: e,
+					},
+				)?;
 			)
 		});
 		// Same as for the input types, we need to check if we also need to convert the output,
@@ -223,7 +231,10 @@ fn generate_native_call_generators(decl: &ItemTrait) -> Result<TokenStream> {
 			quote!(
 				convert_between_block_types(
 					&res,
-					"Could not convert return value from runtime to node!"
+					|e| #crate_::ApiError::FailedToConvertReturnValue {
+						function: #function_name_str,
+						error: e,
+					},
 				)
 			)
 		} else {
@@ -399,10 +410,10 @@ fn generate_call_api_at_calls(decl: &ItemTrait) -> Result<TokenStream> {
 			#[cfg(any(feature = "std", test))]
 			pub fn #fn_name<
 				R: #crate_::Encode + #crate_::Decode + PartialEq,
-				NC: FnOnce() -> std::result::Result<R, String> + std::panic::UnwindSafe,
+				NC: FnOnce() -> std::result::Result<R, #crate_::ApiError> + std::panic::UnwindSafe,
 				Block: #crate_::BlockT,
 				T: #crate_::CallApiAt<Block>,
-				C: #crate_::Core<Block, Error = T::Error>,
+				C: #crate_::Core<Block>,
 			>(
 				call_runtime_at: &T,
 				core_api: &C,
@@ -416,7 +427,7 @@ fn generate_call_api_at_calls(decl: &ItemTrait) -> Result<TokenStream> {
 				native_call: Option<NC>,
 				context: #crate_::ExecutionContext,
 				recorder: &Option<#crate_::ProofRecorder<Block>>,
-			) -> std::result::Result<#crate_::NativeOrEncoded<R>, T::Error> {
+			) -> std::result::Result<#crate_::NativeOrEncoded<R>, #crate_::ApiError> {
 				let version = call_runtime_at.runtime_version_at(at)?;
 				use #crate_::InitializeBlock;
 				let initialize_block = if #skip_initialize_block {
@@ -621,7 +632,7 @@ impl<'a> ToClientSideDecl<'a> {
 					context: #crate_::ExecutionContext,
 					params: Option<( #( #param_types ),* )>,
 					params_encoded: Vec<u8>,
-				) -> std::result::Result<#crate_::NativeOrEncoded<#ret_type>, Self::Error>;
+				) -> std::result::Result<#crate_::NativeOrEncoded<#ret_type>, #crate_::ApiError>;
 			}
 		)
 	}
@@ -647,7 +658,7 @@ impl<'a> ToClientSideDecl<'a> {
 		let params2 = params.clone();
 		let ret_type = return_type_extract_type(&method.sig.output);
 
-		fold_fn_decl_for_client_side(&mut method.sig, &self.block_id);
+		fold_fn_decl_for_client_side(&mut method.sig, &self.block_id, &self.crate_);
 
 		let name_impl = generate_method_runtime_api_impl_name(&self.trait_, &method.sig.ident);
 		let crate_ = self.crate_;
@@ -705,7 +716,12 @@ impl<'a> ToClientSideDecl<'a> {
 							},
 							#crate_::NativeOrEncoded::Encoded(r) => {
 								<#ret_type as #crate_::Decode>::decode(&mut &r[..])
-									.map_err(|err| { #crate_::ApiError::new(#function_name, err).into() })
+									.map_err(|err|
+										#crate_::ApiError::FailedToDecodeReturnValue {
+											function: #function_name,
+											error: err,
+										}
+									)
 							}
 						}
 					)
@@ -728,12 +744,10 @@ impl<'a> Fold for ToClientSideDecl<'a> {
 
 		if is_core_trait {
 			// Add all the supertraits we want to have for `Core`.
-			let crate_ = &self.crate_;
 			input.supertraits = parse_quote!(
 				'static
 				+ Send
 				+ Sync
-				+ #crate_::ApiErrorExt
 			);
 		} else {
 			// Add the `Core` runtime api as super trait.
@@ -803,12 +817,12 @@ fn generate_runtime_info_impl(trait_: &ItemTrait, version: u64) -> TokenStream {
 		let bounds = &t.bounds;
 
 		quote! { #ident #colon_token #bounds }
-	}).chain(std::iter::once(quote! { __Sr_Api_Error__ }));
+	});
 
 	let ty_generics = trait_.generics.type_params().map(|t| {
 		let ident = &t.ident;
 		quote! { #ident }
-	}).chain(std::iter::once(quote! { Error = __Sr_Api_Error__ }));
+	});
 
 	quote!(
 		#[cfg(any(feature = "std", test))]

substrate/primitives/api/proc-macro/src/impl_runtime_apis.rs

@@ -233,16 +233,6 @@ fn generate_runtime_api_base_structures() -> Result<TokenStream> {
 					C::StateBackend: #crate_::StateBackend<#crate_::HashFor<Block>>,
 		{}
 
-		#[cfg(any(feature = "std", test))]
-		impl<Block: #crate_::BlockT, C: #crate_::CallApiAt<Block>> #crate_::ApiErrorExt
-			for RuntimeApiImpl<Block, C>
-				where
-					// Rust bug: https://github.com/rust-lang/rust/issues/24159
-					C::StateBackend: #crate_::StateBackend<#crate_::HashFor<Block>>,
-		{
-			type Error = C::Error;
-		}
-
 		#[cfg(any(feature = "std", test))]
 		impl<Block: #crate_::BlockT, C: #crate_::CallApiAt<Block>> #crate_::ApiExt<Block> for
 			RuntimeApiImpl<Block, C>
@@ -269,16 +259,20 @@ fn generate_runtime_api_base_structures() -> Result<TokenStream> {
 			fn has_api<A: #crate_::RuntimeApiInfo + ?Sized>(
 				&self,
 				at: &#crate_::BlockId<Block>,
-			) -> std::result::Result<bool, C::Error> where Self: Sized {
-				self.call.runtime_version_at(at).map(|v| v.has_api_with(&A::ID, |v| v == A::VERSION))
+			) -> std::result::Result<bool, #crate_::ApiError> where Self: Sized {
+				self.call
+					.runtime_version_at(at)
+					.map(|v| v.has_api_with(&A::ID, |v| v == A::VERSION))
 			}
 
 			fn has_api_with<A: #crate_::RuntimeApiInfo + ?Sized, P: Fn(u32) -> bool>(
 				&self,
 				at: &#crate_::BlockId<Block>,
 				pred: P,
-			) -> std::result::Result<bool, C::Error> where Self: Sized {
-				self.call.runtime_version_at(at).map(|v| v.has_api_with(&A::ID, pred))
+			) -> std::result::Result<bool, #crate_::ApiError> where Self: Sized {
+				self.call
+					.runtime_version_at(at)
+					.map(|v| v.has_api_with(&A::ID, pred))
 			}
 
 			fn record_proof(&mut self) {
@@ -306,7 +300,7 @@ fn generate_runtime_api_base_structures() -> Result<TokenStream> {
 				>>,
 				parent_hash: Block::Hash,
 			) -> std::result::Result<
-				#crate_::StorageChanges<Self::StateBackend, Block>,
+				#crate_::StorageChanges<C::StateBackend, Block>,
 				String
 			> where Self: Sized {
 				self.initialized_block.borrow_mut().take();
@@ -513,7 +507,7 @@ impl<'a> Fold for ApiRuntimeImplToApiRuntimeApiImpl<'a> {
 
 			// Generate the correct return type.
 			input.sig.output = parse_quote!(
-				-> std::result::Result<#crate_::NativeOrEncoded<#ret_type>, RuntimeApiImplCall::Error>
+				-> std::result::Result<#crate_::NativeOrEncoded<#ret_type>, #crate_::ApiError>
 			);
 
 			// Generate the new method implementation that calls into the runtime.
@@ -554,7 +548,7 @@ impl<'a> Fold for ApiRuntimeImplToApiRuntimeApiImpl<'a> {
 			)
 		};
 
-		let mut input =	fold::fold_impl_item_method(self, input);
+		let mut input = fold::fold_impl_item_method(self, input);
 		// We need to set the block, after we modified the rest of the ast, otherwise we would
 		// modify our generated block as well.
 		input.block = block;

substrate/primitives/api/proc-macro/src/mock_impl_runtime_apis.rs

@@ -27,7 +27,7 @@ use proc_macro2::{Span, TokenStream};
 use quote::{quote, quote_spanned};
 
 use syn::{
-	spanned::Spanned, parse_macro_input, Ident, Type, ItemImpl, ImplItem, TypePath, parse_quote,
+	spanned::Spanned, parse_macro_input, Ident, Type, ItemImpl, TypePath, parse_quote,
 	parse::{Parse, ParseStream, Result, Error}, fold::{self, Fold}, Attribute, Pat,
 };
 
@@ -61,29 +61,14 @@ impl Parse for RuntimeApiImpls {
 	}
 }
 
-/// Implement the `ApiExt` trait, `ApiErrorExt` trait and the `Core` runtime api.
+/// Implement the `ApiExt` trait and the `Core` runtime api.
 fn implement_common_api_traits(
-	error_type: Option<Type>,
 	block_type: TypePath,
 	self_ty: Type,
 ) -> Result<TokenStream> {
 	let crate_ = generate_crate_access(HIDDEN_INCLUDES_ID);
 
-	let error_type = error_type
-		.map(|e| quote!(#e))
-		.unwrap_or_else(|| quote!( #crate_::ApiError ) );
-
-	// Quote using the span from `error_type` to generate nice error messages when the type is
-	// not implementing a trait or similar.
-	let api_error_ext = quote_spanned! { error_type.span() =>
-		impl #crate_::ApiErrorExt for #self_ty {
-			type Error = #error_type;
-		}
-	};
-
 	Ok(quote!(
-		#api_error_ext
-
 		impl #crate_::ApiExt<#block_type> for #self_ty {
 			type StateBackend = #crate_::InMemoryBackend<#crate_::HashFor<#block_type>>;
 
@@ -97,7 +82,7 @@ fn implement_common_api_traits(
 			fn has_api<A: #crate_::RuntimeApiInfo + ?Sized>(
 				&self,
 				_: &#crate_::BlockId<#block_type>,
-			) -> std::result::Result<bool, #error_type> where Self: Sized {
+			) -> std::result::Result<bool, #crate_::ApiError> where Self: Sized {
 				Ok(true)
 			}
 
@@ -105,7 +90,7 @@ fn implement_common_api_traits(
 				&self,
 				_: &#crate_::BlockId<#block_type>,
 				pred: P,
-			) -> std::result::Result<bool, #error_type> where Self: Sized {
+			) -> std::result::Result<bool, #crate_::ApiError> where Self: Sized {
 				Ok(pred(A::VERSION))
 			}
 
@@ -140,7 +125,7 @@ fn implement_common_api_traits(
 				_: #crate_::ExecutionContext,
 				_: Option<()>,
 				_: Vec<u8>,
-			) -> std::result::Result<#crate_::NativeOrEncoded<#crate_::RuntimeVersion>, #error_type> {
+			) -> std::result::Result<#crate_::NativeOrEncoded<#crate_::RuntimeVersion>, #crate_::ApiError> {
 				unimplemented!("Not required for testing!")
 			}
 
@@ -150,7 +135,7 @@ fn implement_common_api_traits(
 				_: #crate_::ExecutionContext,
 				_: Option<#block_type>,
 				_: Vec<u8>,
-			) -> std::result::Result<#crate_::NativeOrEncoded<()>, #error_type> {
+			) -> std::result::Result<#crate_::NativeOrEncoded<()>, #crate_::ApiError> {
 				unimplemented!("Not required for testing!")
 			}
 
@@ -160,7 +145,7 @@ fn implement_common_api_traits(
 				_: #crate_::ExecutionContext,
 				_: Option<&<#block_type as #crate_::BlockT>::Header>,
 				_: Vec<u8>,
-			) -> std::result::Result<#crate_::NativeOrEncoded<()>, #error_type> {
+			) -> std::result::Result<#crate_::NativeOrEncoded<()>, #crate_::ApiError> {
 				unimplemented!("Not required for testing!")
 			}
 		}
@@ -230,9 +215,6 @@ struct FoldRuntimeApiImpl<'a> {
 	block_type: &'a TypePath,
 	/// The identifier of the trait being implemented.
 	impl_trait: &'a Ident,
-	/// Stores the error type that is being found in the trait implementation as associated type
-	/// with the name `Error`.
-	error_type: &'a mut Option<Type>,
 }
 
 impl<'a> Fold for FoldRuntimeApiImpl<'a> {
@@ -300,7 +282,7 @@ impl<'a> Fold for FoldRuntimeApiImpl<'a> {
 
 				// Generate the correct return type.
 				input.sig.output = parse_quote!(
-					-> std::result::Result<#crate_::NativeOrEncoded<#ret_type>, Self::Error>
+					-> std::result::Result<#crate_::NativeOrEncoded<#ret_type>, #crate_::ApiError>
 				);
 			}
 
@@ -336,51 +318,12 @@ impl<'a> Fold for FoldRuntimeApiImpl<'a> {
 		input.block = block;
 		input
 	}
-
-	fn fold_impl_item(&mut self, input: ImplItem) -> ImplItem {
-		match input {
-			ImplItem::Type(ty) => {
-				if ty.ident == "Error" {
-					if let Some(error_type) = self.error_type {
-						if *error_type != ty.ty {
-							let mut error = Error::new(
-								ty.span(),
-								"Error type can not change between runtime apis",
-							);
-							let error_first = Error::new(
-								error_type.span(),
-								"First error type was declared here."
-							);
-
-							error.combine(error_first);
-
-							ImplItem::Verbatim(error.to_compile_error())
-						} else {
-							ImplItem::Verbatim(Default::default())
-						}
-					} else {
-						*self.error_type = Some(ty.ty);
-						ImplItem::Verbatim(Default::default())
-					}
-				} else {
-					let error = Error::new(
-						ty.span(),
-						"Only associated type with name `Error` is allowed",
-					);
-					ImplItem::Verbatim(error.to_compile_error())
-				}
-			},
-			o => fold::fold_impl_item(self, o),
-		}
-	}
 }
 
 /// Result of [`generate_runtime_api_impls`].
 struct GeneratedRuntimeApiImpls {
 	/// All the runtime api implementations.
 	impls: TokenStream,
-	/// The error type that should be used by the runtime apis.
-	error_type: Option<Type>,
 	/// The block type that is being used by the runtime apis.
 	block_type: TypePath,
 	/// The type the traits are implemented for.
@@ -393,7 +336,6 @@ struct GeneratedRuntimeApiImpls {
 /// extracts the error type, self type and the block type.
 fn generate_runtime_api_impls(impls: &[ItemImpl]) -> Result<GeneratedRuntimeApiImpls> {
 	let mut result = Vec::with_capacity(impls.len());
-	let mut error_type = None;
 	let mut global_block_type: Option<TypePath> = None;
 	let mut self_ty: Option<Box<Type>> = None;
 
@@ -451,7 +393,6 @@ fn generate_runtime_api_impls(impls: &[ItemImpl]) -> Result<GeneratedRuntimeApiI
 		let mut visitor = FoldRuntimeApiImpl {
 			block_type,
 			impl_trait: &impl_trait.ident,
-			error_type: &mut error_type,
 		};
 
 		result.push(visitor.fold_item_impl(impl_.clone()));
@@ -459,7 +400,6 @@ fn generate_runtime_api_impls(impls: &[ItemImpl]) -> Result<GeneratedRuntimeApiI
 
 	Ok(GeneratedRuntimeApiImpls {
 		impls: quote!( #( #result )* ),
-		error_type,
 		block_type: global_block_type.expect("There is a least one runtime api; qed"),
 		self_ty: *self_ty.expect("There is at least one runtime api; qed"),
 	})
@@ -475,9 +415,9 @@ pub fn mock_impl_runtime_apis_impl(input: proc_macro::TokenStream) -> proc_macro
 
 fn mock_impl_runtime_apis_impl_inner(api_impls: &[ItemImpl]) -> Result<TokenStream> {
 	let hidden_includes = generate_hidden_includes(HIDDEN_INCLUDES_ID);
-	let GeneratedRuntimeApiImpls { impls, error_type, block_type, self_ty } =
+	let GeneratedRuntimeApiImpls { impls, block_type, self_ty } =
 		generate_runtime_api_impls(api_impls)?;
-	let api_traits = implement_common_api_traits(error_type, block_type, self_ty)?;
+	let api_traits = implement_common_api_traits(block_type, self_ty)?;
 
 	Ok(quote!(
 		#hidden_includes

substrate/primitives/api/proc-macro/src/utils.rs

@@ -99,6 +99,7 @@ pub fn replace_wild_card_parameter_names(input: &mut Signature) {
 pub fn fold_fn_decl_for_client_side(
 	input: &mut Signature,
 	block_id: &TokenStream,
+	crate_: &TokenStream,
 ) {
 	replace_wild_card_parameter_names(input);
 
@@ -109,7 +110,7 @@ pub fn fold_fn_decl_for_client_side(
 	// Wrap the output in a `Result`
 	input.output = {
 		let ty = return_type_extract_type(&input.output);
-		parse_quote!( -> std::result::Result<#ty, Self::Error> )
+		parse_quote!( -> std::result::Result<#ty, #crate_::ApiError> )
 	};
 }
 

substrate/primitives/api/src/lib.rs

@@ -67,7 +67,7 @@ pub use sp_std::{slice, mem};
 #[cfg(feature = "std")]
 use sp_std::result;
 #[doc(hidden)]
-pub use codec::{Encode, Decode, DecodeLimit};
+pub use codec::{Encode, Decode, DecodeLimit, self};
 use sp_core::OpaqueMetadata;
 #[cfg(feature = "std")]
 use std::{panic::UnwindSafe, cell::RefCell};
@@ -246,8 +246,8 @@ pub use sp_api_proc_macro::impl_runtime_apis;
 /// and the error type can be specified as associated type. If no error type is specified [`String`]
 /// is used as error type.
 ///
-/// Besides implementing the given traits, the [`Core`](sp_api::Core), [`ApiExt`](sp_api::ApiExt)
-/// and [`ApiErrorExt`](sp_api::ApiErrorExt) are implemented automatically.
+/// Besides implementing the given traits, the [`Core`](sp_api::Core) and [`ApiExt`](sp_api::ApiExt)
+/// are implemented automatically.
 ///
 /// # Example
 ///
@@ -284,11 +284,6 @@ pub use sp_api_proc_macro::impl_runtime_apis;
 ///     }
 ///
 ///     impl BlockBuilder<Block> for MockApi {
-///         /// Sets the error type that is being used by the mock implementation.
-///         /// The error type is used by all runtime apis. It is only required to
-///         /// be specified in one trait implementation.
-///         type Error = sp_api::ApiError;
-///
 ///         fn build_block() -> Block {
 ///              unimplemented!("Not Required in tests")
 ///         }
@@ -331,15 +326,14 @@ pub use sp_api_proc_macro::impl_runtime_apis;
 ///
 /// sp_api::mock_impl_runtime_apis! {
 ///     impl Balance<Block> for MockApi {
-///         type Error = sp_api::ApiError;
 ///         #[advanced]
-///         fn get_balance(&self, at: &BlockId<Block>) -> Result<NativeOrEncoded<u64>, Self::Error> {
+///         fn get_balance(&self, at: &BlockId<Block>) -> Result<NativeOrEncoded<u64>, sp_api::ApiError> {
 ///             println!("Being called at: {}", at);
 ///
 ///             Ok(self.balance.into())
 ///         }
 ///         #[advanced]
-///         fn set_balance(at: &BlockId<Block>, val: u64) -> Result<NativeOrEncoded<()>, Self::Error> {
+///         fn set_balance(at: &BlockId<Block>, val: u64) -> Result<NativeOrEncoded<()>, sp_api::ApiError> {
 ///             if let BlockId::Number(1) = at {
 ///                 println!("Being called to set balance to: {}", val);
 ///             }
@@ -393,46 +387,35 @@ pub trait ConstructRuntimeApi<Block: BlockT, C: CallApiAt<Block>> {
 }
 
 /// An error describing which API call failed.
-#[cfg_attr(feature = "std", derive(Debug, thiserror::Error, Eq, PartialEq))]
-#[cfg_attr(feature = "std", error("Failed to execute API call {tag}"))]
 #[cfg(feature = "std")]
-pub struct ApiError {
-    tag: &'static str,
-    #[source]
-    error: codec::Error,
-}
-
-#[cfg(feature = "std")]
-impl From<(&'static str, codec::Error)> for ApiError {
-    fn from((tag, error): (&'static str, codec::Error)) -> Self {
-        Self {
-            tag,
-            error,
-        }
-    }
-}
-
-#[cfg(feature = "std")]
-impl ApiError {
-	pub fn new(tag: &'static str, error: codec::Error) -> Self {
-		Self {
-			tag,
-			error,
-		}
-	}
-}
-
-/// Extends the runtime api traits with an associated error type. This trait is given as super
-/// trait to every runtime api trait.
-#[cfg(feature = "std")]
-pub trait ApiErrorExt {
-	/// Error type used by the runtime apis.
-	type Error: std::fmt::Debug + From<ApiError>;
+#[derive(Debug, thiserror::Error)]
+pub enum ApiError {
+	#[error("Failed to decode return value of {function}")]
+	FailedToDecodeReturnValue {
+		function: &'static str,
+		#[source]
+		error: codec::Error,
+	},
+	#[error("Failed to convert return value from runtime to node of {function}")]
+	FailedToConvertReturnValue {
+		function: &'static str,
+		#[source]
+		error: codec::Error,
+	},
+	#[error("Failed to convert parameter `{parameter}` from node to runtime of {function}")]
+	FailedToConvertParameter {
+		function: &'static str,
+		parameter: &'static str,
+		#[source]
+		error: codec::Error,
+	},
+	#[error(transparent)]
+	Application(#[from] Box<dyn std::error::Error + Send + Sync>),
 }
 
 /// Extends the runtime api implementation with some common functionality.
 #[cfg(feature = "std")]
-pub trait ApiExt<Block: BlockT>: ApiErrorExt {
+pub trait ApiExt<Block: BlockT> {
 	/// The state backend that is used to store the block states.
 	type StateBackend: StateBackend<HashFor<Block>>;
 
@@ -450,14 +433,14 @@ pub trait ApiExt<Block: BlockT>: ApiErrorExt {
 	fn has_api<A: RuntimeApiInfo + ?Sized>(
 		&self,
 		at: &BlockId<Block>,
-	) -> Result<bool, Self::Error> where Self: Sized;
+	) -> Result<bool, ApiError> where Self: Sized;
 
 	/// Check if the given api is implemented and the version passes a predicate.
 	fn has_api_with<A: RuntimeApiInfo + ?Sized, P: Fn(u32) -> bool>(
 		&self,
 		at: &BlockId<Block>,
 		pred: P,
-	) -> Result<bool, Self::Error> where Self: Sized;
+	) -> Result<bool, ApiError> where Self: Sized;
 
 	/// Start recording all accessed trie nodes for generating proofs.
 	fn record_proof(&mut self);
@@ -478,7 +461,10 @@ pub trait ApiExt<Block: BlockT>: ApiErrorExt {
 		backend: &Self::StateBackend,
 		changes_trie_state: Option<&ChangesTrieState<HashFor<Block>, NumberFor<Block>>>,
 		parent_hash: Block::Hash,
-	) -> Result<StorageChanges<Self::StateBackend, Block>, String> where Self: Sized;
+	) -> Result<
+		StorageChanges<Self::StateBackend, Block>,
+		String
+	> where Self: Sized;
 }
 
 /// Before calling any runtime api function, the runtime need to be initialized
@@ -533,9 +519,6 @@ pub struct CallApiAtParams<'a, Block: BlockT, C, NC, Backend: StateBackend<HashF
 /// Something that can call into the an api at a given block.
 #[cfg(feature = "std")]
 pub trait CallApiAt<Block: BlockT> {
-	/// Error type used by the implementation.
-	type Error: std::fmt::Debug + From<ApiError>;
-
 	/// The state backend that is used to store the block states.
 	type StateBackend: StateBackend<HashFor<Block>>;
 
@@ -544,15 +527,18 @@ pub trait CallApiAt<Block: BlockT> {
 	fn call_api_at<
 		'a,
 		R: Encode + Decode + PartialEq,
-		NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
-		C: Core<Block, Error = Self::Error>,
+		NC: FnOnce() -> result::Result<R, ApiError> + UnwindSafe,
+		C: Core<Block>,
 	>(
 		&self,
 		params: CallApiAtParams<'a, Block, C, NC, Self::StateBackend>,
-	) -> Result<NativeOrEncoded<R>, Self::Error>;
+	) -> Result<NativeOrEncoded<R>, ApiError>;
 
 	/// Returns the runtime version at the given block.
-	fn runtime_version_at(&self, at: &BlockId<Block>) -> Result<RuntimeVersion, Self::Error>;
+	fn runtime_version_at(
+		&self,
+		at: &BlockId<Block>,
+	) -> Result<RuntimeVersion, ApiError>;
 }
 
 /// Auxiliary wrapper that holds an api instance and binds it to the given lifetime.
@@ -605,10 +591,6 @@ pub trait RuntimeApiInfo {
 	const VERSION: u32;
 }
 
-/// Extracts the `Api::Error` for a type that provides a runtime api.
-#[cfg(feature = "std")]
-pub type ApiErrorFor<T, Block> = <<T as ProvideRuntimeApi<Block>>::Api as ApiErrorExt>::Error;
-
 #[derive(codec::Encode, codec::Decode)]
 pub struct OldRuntimeVersion {
 	pub spec_name: RuntimeString,

substrate/primitives/api/test/tests/decl_and_impl.rs

@@ -23,7 +23,6 @@ use sp_api::{
 use sp_runtime::{traits::{GetNodeBlockType, Block as BlockT}, generic::BlockId};
 use sp_core::NativeOrEncoded;
 use substrate_test_runtime_client::runtime::Block;
-use sp_blockchain::Result;
 
 /// The declaration of the `Runtime` type and the implementation of the `GetNodeBlockType`
 /// trait are done by the `construct_runtime!` macro in a real runtime.
@@ -105,7 +104,7 @@ mock_impl_runtime_apis! {
 
 		#[advanced]
 		fn same_name(_: &BlockId<Block>) ->
-			std::result::Result<
+			Result<
 				NativeOrEncoded<()>,
 				ApiError
 			>
@@ -115,7 +114,7 @@ mock_impl_runtime_apis! {
 
 		#[advanced]
 		fn wild_card(at: &BlockId<Block>, _: u32) ->
-			std::result::Result<
+			Result<
 				NativeOrEncoded<()>,
 				ApiError
 			>
@@ -124,7 +123,7 @@ mock_impl_runtime_apis! {
 				// yeah
 				Ok(().into())
 			} else {
-				Err(ApiError::new("MockApi", codec::Error::from("Ohh noooo")))
+				Err((Box::from("Test error") as Box<dyn std::error::Error + Send + Sync>).into())
 			}
 		}
 	}
@@ -143,33 +142,33 @@ type TestClient = substrate_test_runtime_client::client::Client<
 
 #[test]
 fn test_client_side_function_signature() {
-	let _test: fn(&RuntimeApiImpl<Block, TestClient>, &BlockId<Block>, u64) -> Result<()> =
+	let _test: fn(&RuntimeApiImpl<Block, TestClient>, &BlockId<Block>, u64) -> Result<(), ApiError> =
 		RuntimeApiImpl::<Block, TestClient>::test;
 	let _something_with_block:
-		fn(&RuntimeApiImpl<Block, TestClient>, &BlockId<Block>, Block) -> Result<Block> =
+		fn(&RuntimeApiImpl<Block, TestClient>, &BlockId<Block>, Block) -> Result<Block, ApiError> =
 			RuntimeApiImpl::<Block, TestClient>::something_with_block;
 
 	#[allow(deprecated)]
 	let _same_name_before_version_2:
-		fn(&RuntimeApiImpl<Block, TestClient>, &BlockId<Block>) -> Result<String> =
+		fn(&RuntimeApiImpl<Block, TestClient>, &BlockId<Block>) -> Result<String, ApiError> =
 			RuntimeApiImpl::<Block, TestClient>::same_name_before_version_2;
 }
 
 #[test]
 fn check_runtime_api_info() {
-	assert_eq!(&Api::<Block, Error = ()>::ID, &runtime_decl_for_Api::ID);
-	assert_eq!(Api::<Block, Error = ()>::VERSION, runtime_decl_for_Api::VERSION);
-	assert_eq!(Api::<Block, Error = ()>::VERSION, 1);
+	assert_eq!(&Api::<Block>::ID, &runtime_decl_for_Api::ID);
+	assert_eq!(Api::<Block>::VERSION, runtime_decl_for_Api::VERSION);
+	assert_eq!(Api::<Block>::VERSION, 1);
 
 	assert_eq!(
-		ApiWithCustomVersion::<Block, Error = ()>::VERSION,
+		ApiWithCustomVersion::<Block>::VERSION,
 		runtime_decl_for_ApiWithCustomVersion::VERSION,
 	);
 	assert_eq!(
-		&ApiWithCustomVersion::<Block, Error = ()>::ID,
+		&ApiWithCustomVersion::<Block>::ID,
 		&runtime_decl_for_ApiWithCustomVersion::ID,
 	);
-	assert_eq!(ApiWithCustomVersion::<Block, Error = ()>::VERSION, 2);
+	assert_eq!(ApiWithCustomVersion::<Block>::VERSION, 2);
 }
 
 fn check_runtime_api_versions_contains<T: RuntimeApiInfo + ?Sized>() {
@@ -178,9 +177,9 @@ fn check_runtime_api_versions_contains<T: RuntimeApiInfo + ?Sized>() {
 
 #[test]
 fn check_runtime_api_versions() {
-	check_runtime_api_versions_contains::<dyn Api<Block, Error = ()>>();
-	check_runtime_api_versions_contains::<dyn ApiWithCustomVersion<Block, Error = ()>>();
-	check_runtime_api_versions_contains::<dyn sp_api::Core<Block, Error = ()>>();
+	check_runtime_api_versions_contains::<dyn Api<Block>>();
+	check_runtime_api_versions_contains::<dyn ApiWithCustomVersion<Block>>();
+	check_runtime_api_versions_contains::<dyn sp_api::Core<Block>>();
 }
 
 #[test]
@@ -188,9 +187,9 @@ fn mock_runtime_api_has_api() {
 	let mock = MockApi { block: None };
 
 	assert!(
-		mock.has_api::<dyn ApiWithCustomVersion<Block, Error = ()>>(&BlockId::Number(0)).unwrap(),
+		mock.has_api::<dyn ApiWithCustomVersion<Block>>(&BlockId::Number(0)).unwrap(),
 	);
-	assert!(mock.has_api::<dyn Api<Block, Error = ()>>(&BlockId::Number(0)).unwrap());
+	assert!(mock.has_api::<dyn Api<Block>>(&BlockId::Number(0)).unwrap());
 }
 
 #[test]
@@ -209,7 +208,7 @@ fn mock_runtime_api_works_with_advanced() {
 	Api::<Block>::same_name(&mock, &BlockId::Number(0)).unwrap();
 	mock.wild_card(&BlockId::Number(1337), 1).unwrap();
 	assert_eq!(
-		ApiError::new("MockApi", ::codec::Error::from("Ohh noooo")),
-		mock.wild_card(&BlockId::Number(1336), 1).unwrap_err()
+		"Test error".to_string(),
+		mock.wild_card(&BlockId::Number(1336), 1).unwrap_err().to_string(),
 	);
 }

substrate/primitives/api/test/tests/runtime_calls.rs

@@ -50,10 +50,7 @@ fn calling_wasm_runtime_function() {
 }
 
 #[test]
-#[should_panic(
-	expected =
-		"Could not convert parameter `param` between node and runtime: DecodeFails always fails"
-)]
+#[should_panic(expected = "FailedToConvertParameter { function: \"fail_convert_parameter\"")]
 fn calling_native_runtime_function_with_non_decodable_parameter() {
 	let client = TestClientBuilder::new().set_execution_strategy(ExecutionStrategy::NativeWhenPossible).build();
 	let runtime_api = client.runtime_api();
@@ -62,7 +59,7 @@ fn calling_native_runtime_function_with_non_decodable_parameter() {
 }
 
 #[test]
-#[should_panic(expected = "Could not convert return value from runtime to node!")]
+#[should_panic(expected = "FailedToConvertReturnValue { function: \"fail_convert_return_value\"")]
 fn calling_native_runtime_function_with_non_decodable_return_value() {
 	let client = TestClientBuilder::new().set_execution_strategy(ExecutionStrategy::NativeWhenPossible).build();
 	let runtime_api = client.runtime_api();

substrate/primitives/api/test/tests/ui/mock_only_error_associated_type.rs

@@ -1,19 +0,0 @@
-use substrate_test_runtime_client::runtime::Block;
-
-sp_api::decl_runtime_apis! {
-	pub trait Api {
-		fn test(data: u64);
-	}
-}
-
-struct MockApi;
-
-sp_api::mock_impl_runtime_apis! {
-	impl Api<Block> for MockApi {
-		type OtherData = u32;
-
-		fn test(data: u64) {}
-	}
-}
-
-fn main() {}

substrate/primitives/api/test/tests/ui/mock_only_error_associated_type.stderr

@@ -1,5 +0,0 @@
-error: Only associated type with name `Error` is allowed
-  --> $DIR/mock_only_error_associated_type.rs:13:3
-   |
-13 |         type OtherData = u32;
-   |         ^^^^

substrate/primitives/api/test/tests/ui/mock_only_one_error_type.rs

@@ -1,29 +0,0 @@
-use substrate_test_runtime_client::runtime::Block;
-
-sp_api::decl_runtime_apis! {
-	pub trait Api {
-		fn test(data: u64);
-	}
-
-	pub trait Api2 {
-		fn test(data: u64);
-	}
-}
-
-struct MockApi;
-
-sp_api::mock_impl_runtime_apis! {
-	impl Api<Block> for MockApi {
-		type Error = u32;
-
-		fn test(data: u64) {}
-	}
-
-	impl Api2<Block> for MockApi {
-		type Error = u64;
-
-		fn test(data: u64) {}
-	}
-}
-
-fn main() {}

substrate/primitives/api/test/tests/ui/mock_only_one_error_type.stderr

@@ -1,29 +0,0 @@
-error: Error type can not change between runtime apis
-  --> $DIR/mock_only_one_error_type.rs:23:3
-   |
-23 |         type Error = u64;
-   |         ^^^^
-
-error: First error type was declared here.
-  --> $DIR/mock_only_one_error_type.rs:17:16
-   |
-17 |         type Error = u32;
-   |                      ^^^
-
-error[E0277]: the trait bound `u32: From<sp_api_hidden_includes_DECL_RUNTIME_APIS::sp_api::ApiError>` is not satisfied
-   --> $DIR/mock_only_one_error_type.rs:17:16
-    |
-17  |         type Error = u32;
-    |                      ^^^ the trait `From<sp_api_hidden_includes_DECL_RUNTIME_APIS::sp_api::ApiError>` is not implemented for `u32`
-    |
-   ::: $WORKSPACE/primitives/api/src/lib.rs
-    |
-    |     type Error: std::fmt::Debug + From<ApiError>;
-    |                                   -------------- required by this bound in `sp_api_hidden_includes_DECL_RUNTIME_APIS::sp_api::ApiErrorExt::Error`
-    |
-    = help: the following implementations were found:
-              <u32 as From<HttpError>>
-              <u32 as From<HttpRequestId>>
-              <u32 as From<HttpRequestStatus>>
-              <u32 as From<Ipv4Addr>>
-            and 18 others

substrate/primitives/blockchain/src/error.rs

@@ -114,8 +114,8 @@ pub enum Error {
 	#[error("Error decoding call result of {0}")]
 	CallResultDecode(&'static str, #[source] CodecError),
 
-	#[error(transparent)]
-	RuntimeApiCodecError(#[from] ApiError),
+	#[error("Error at calling runtime api: {0}")]
+	RuntimeApiError(#[from] ApiError),
 
 	#[error("Runtime :code missing in storage")]
 	RuntimeCodeMissing,
@@ -153,7 +153,6 @@ pub enum Error {
 	#[error("Failed to get header for hash {0}")]
 	MissingHeader(String),
 
-
 	#[error("State Database error: {0}")]
 	StateDatabase(String),
 
@@ -183,6 +182,15 @@ impl From<Box<dyn sp_state_machine::Error>> for Error {
 	}
 }
 
+impl From<Error> for ApiError {
+	fn from(err: Error) -> ApiError {
+		match err {
+			Error::RuntimeApiError(err) => err,
+			e => ApiError::Application(Box::new(e)),
+		}
+	}
+}
+
 impl Error {
 	/// Chain a blockchain error.
 	pub fn from_blockchain(e: Box<Error>) -> Self {

substrate/primitives/core/src/traits.rs

@@ -34,7 +34,7 @@ pub trait CodeExecutor: Sized + Send + Sync + CallInWasm + Clone + 'static {
 	/// or an execution error) together with a `bool`, which is true if native execution was used.
 	fn call<
 		R: codec::Codec + PartialEq,
-		NC: FnOnce() -> Result<R, String> + UnwindSafe,
+		NC: FnOnce() -> Result<R, Box<dyn std::error::Error + Send + Sync>> + UnwindSafe,
 	>(
 		&self,
 		ext: &mut dyn Externalities,

substrate/primitives/session/src/lib.rs

@@ -113,7 +113,7 @@ pub fn generate_initial_session_keys<Block, T>(
 	client: std::sync::Arc<T>,
 	at: &BlockId<Block>,
 	seeds: Vec<String>,
-) -> Result<(), sp_api::ApiErrorFor<T, Block>>
+) -> Result<(), sp_api::ApiError>
 where
 	Block: BlockT,
 	T: ProvideRuntimeApi<Block>,

substrate/primitives/state-machine/src/lib.rs

@@ -392,7 +392,7 @@ mod execution {
 			bool,
 		) where
 			R: Decode + Encode + PartialEq,
-			NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+			NC: FnOnce() -> result::Result<R, Box<dyn std::error::Error + Send + Sync>> + UnwindSafe,
 		{
 			let mut cache = StorageTransactionCache::default();
 
@@ -449,7 +449,7 @@ mod execution {
 		) -> CallResult<R, Exec::Error>
 			where
 				R: Decode + Encode + PartialEq,
-				NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+				NC: FnOnce() -> result::Result<R, Box<dyn std::error::Error + Send + Sync>> + UnwindSafe,
 				Handler: FnOnce(
 					CallResult<R, Exec::Error>,
 					CallResult<R, Exec::Error>,
@@ -485,7 +485,7 @@ mod execution {
 		) -> CallResult<R, Exec::Error>
 			where
 				R: Decode + Encode + PartialEq,
-				NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+				NC: FnOnce() -> result::Result<R, Box<dyn std::error::Error + Send + Sync>> + UnwindSafe,
 		{
 			self.overlay.start_transaction();
 			let (result, was_native) = self.execute_aux(
@@ -522,7 +522,7 @@ mod execution {
 		) -> Result<NativeOrEncoded<R>, Box<dyn Error>>
 			where
 				R: Decode + Encode + PartialEq,
-				NC: FnOnce() -> result::Result<R, String> + UnwindSafe,
+				NC: FnOnce() -> result::Result<R, Box<dyn std::error::Error + Send + Sync>> + UnwindSafe,
 				Handler: FnOnce(
 					CallResult<R, Exec::Error>,
 					CallResult<R, Exec::Error>,
@@ -869,7 +869,7 @@ mod tests {
 		map, traits::{Externalities, RuntimeCode}, testing::TaskExecutor,
 	};
 	use sp_runtime::traits::BlakeTwo256;
-	use std::{result, collections::HashMap};
+	use std::{result, collections::HashMap, panic::UnwindSafe};
 	use codec::Decode;
 	use sp_core::{
 		storage::ChildInfo, NativeOrEncoded, NeverNativeValue,
@@ -891,7 +891,7 @@ mod tests {
 
 		fn call<
 			R: Encode + Decode + PartialEq,
-			NC: FnOnce() -> result::Result<R, String>,
+			NC: FnOnce() -> result::Result<R, Box<dyn std::error::Error + Send + Sync>> + UnwindSafe,
 		>(
 			&self,
 			ext: &mut dyn Externalities,

substrate/test-utils/runtime/client/src/block_builder_ext.rs

@@ -43,7 +43,7 @@ pub trait BlockBuilderExt {
 
 impl<'a, A, B> BlockBuilderExt for sc_block_builder::BlockBuilder<'a, substrate_test_runtime::Block, A, B> where
 	A: ProvideRuntimeApi<substrate_test_runtime::Block> + 'a,
-	A::Api: BlockBuilderApi<substrate_test_runtime::Block, Error = sp_blockchain::Error> +
+	A::Api: BlockBuilderApi<substrate_test_runtime::Block> +
 		ApiExt<
 			substrate_test_runtime::Block,
 			StateBackend = backend::StateBackendFor<B, substrate_test_runtime::Block>