Metadata V15: Expose types for the overarching Call, Event, Error enums (#14143)

* frame-metadata: Point to unreleased branch

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame: Generalize outer enum generation for events and errors

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame: Remove individual generation of outer enum events

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* primitives/traits: Add marker trait for outer runtime enums

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame: Derive Clone, PartialEq, Eq for RuntimeEvents only

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/pallet: Include `#[pallet::error]` enum into pallet parts

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* metadata-ir: Include call, event, error types

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/metadata: Include outer enum types in V15 metadata

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/tests: Ensure `RuntimeError` includes `#[pallet::error]` parts

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/support: Document the reserved name for `RuntimeError`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame: Use self-generated `RuntimeEvent` for `GetRuntimeOuterEnumTypes`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/ui: Fix UI tests

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/support: Remove unused system path

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/ui: Unexpected field and reintroduce frame_system::Config for RuntimeCall

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/support: Remove `GetRuntimeOuterEnumTypes` marker trait

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/support: Remove `;` from macro

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update frame-metadata to point to unreleased branch

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Rename error_enum_ty to module_error_enum_ty

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update module_error_ty documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame: Implement from_dispatch_error

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/support: Adjust test to ModuleErrorType

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Fix clippy

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Improve documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame/tests: Check `from_dispatch_error` impl

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update frame-metadata

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Remove the module_error_ty

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Apply fmt

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Revert unneeded parts

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Revert "Revert unneeded parts"

This reverts commit b94bbd16078a025775a48da1095edec1705e6a4d.

Revert "Apply fmt"

This reverts commit 9b1c3e7b4ef27d32e10b35054a99916067e0397b.

Revert "Remove the module_error_ty"

This reverts commit 98de5b24653f9f9ec6ee842b749401b18a01758a.

* Update frame-metadata to origin/master

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Add outerEnums to the metadata

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Add tests

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Keep backwards compatibility for explicit pallet parts

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Rename tt_error_part to be more generic

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Increase recursion_limit to 1k

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Rename `fully_expanded` to `expanded`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Improve documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Adjust UI tests

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update UI tests

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update undefined_validate_unsigned_part.stderr UI test

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Adjust yet again

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Optimise macro expansions

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Use latest frame-metadata and rename `moduleErrorType` to `RuntimeError`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Fix comment

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Apply fmt

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update frame/support/procedural/src/construct_runtime/parse.rs

Co-authored-by: Bastian Köcher <git@kchr.de>

* Update frame/support/procedural/src/construct_runtime/parse.rs

Co-authored-by: Bastian Köcher <git@kchr.de>

* Update frame-metadata PR

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Remove `expanded` from error messages and fix typo

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Move docs to the function

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* ui: Use the intermed syntax for pallet parts

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update frame-metadata with latest release

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* frame: Address feedback for `from_dispatch_error`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/Cargo.lock

@@ -2697,9 +2697,9 @@ dependencies = [
 
 [[package]]
 name = "frame-metadata"
-version = "15.1.0"
+version = "15.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "878babb0b136e731cc77ec2fd883ff02745ff21e6fb662729953d44923df009c"
+checksum = "f2a893ede8dde2293e94dacf9c8f5db5d0506cd909257a8f0ac2b7d610baf50c"
 dependencies = [
  "cfg-if",
  "parity-scale-codec",

substrate/bin/node/runtime/src/lib.rs

@@ -19,8 +19,8 @@
 //! The Substrate runtime. This can be compiled with `#[no_std]`, ready for Wasm.
 
 #![cfg_attr(not(feature = "std"), no_std)]
-// `construct_runtime!` does a lot of recursion and requires us to increase the limit to 512.
-#![recursion_limit = "512"]
+// `construct_runtime!` does a lot of recursion and requires us to increase the limits.
+#![recursion_limit = "1024"]
 
 use codec::{Decode, Encode, MaxEncodedLen};
 use frame_election_provider_support::{

substrate/frame/support/Cargo.toml

@@ -16,7 +16,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 serde = { version = "1.0.163", default-features = false, features = ["alloc", "derive"] }
 codec = { package = "parity-scale-codec", version = "3.6.1", default-features = false, features = ["derive", "max-encoded-len"] }
 scale-info = { version = "2.5.0", default-features = false, features = ["derive"] }
-frame-metadata = { version = "15.1.0", default-features = false, features = ["v14", "v15-unstable"] }
+frame-metadata = { version = "15.2.0", default-features = false, features = ["unstable"] }
 sp-api = { version = "4.0.0-dev", default-features = false, path = "../../primitives/api" }
 sp-std = { version = "8.0.0", default-features = false, path = "../../primitives/std" }
 sp-io = { version = "23.0.0", default-features = false, path = "../../primitives/io" }

substrate/frame/support/procedural/src/construct_runtime/expand/event.rs

@@ -1,168 +0,0 @@
-// This file is part of Substrate.
-
-// Copyright (C) Parity Technologies (UK) Ltd.
-// SPDX-License-Identifier: Apache-2.0
-
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-// 	http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License
-
-use crate::construct_runtime::Pallet;
-use proc_macro2::TokenStream;
-use quote::quote;
-use std::str::FromStr;
-use syn::{Generics, Ident};
-
-pub fn expand_outer_event(
-	runtime: &Ident,
-	pallet_decls: &[Pallet],
-	scrate: &TokenStream,
-) -> syn::Result<TokenStream> {
-	let mut event_variants = TokenStream::new();
-	let mut event_conversions = TokenStream::new();
-	let mut query_event_part_macros = Vec::new();
-
-	for pallet_decl in pallet_decls {
-		if let Some(pallet_entry) = pallet_decl.find_part("Event") {
-			let path = &pallet_decl.path;
-			let pallet_name = &pallet_decl.name;
-			let index = pallet_decl.index;
-			let instance = pallet_decl.instance.as_ref();
-			let generics = &pallet_entry.generics;
-
-			if instance.is_some() && generics.params.is_empty() {
-				let msg = format!(
-					"Instantiable pallet with no generic `Event` cannot \
-					 be constructed: pallet `{}` must have generic `Event`",
-					pallet_name,
-				);
-				return Err(syn::Error::new(pallet_name.span(), msg))
-			}
-
-			let part_is_generic = !generics.params.is_empty();
-			let pallet_event = match (instance, part_is_generic) {
-				(Some(inst), true) => quote!(#path::Event::<#runtime, #path::#inst>),
-				(Some(inst), false) => quote!(#path::Event::<#path::#inst>),
-				(None, true) => quote!(#path::Event::<#runtime>),
-				(None, false) => quote!(#path::Event),
-			};
-
-			event_variants.extend(expand_event_variant(
-				runtime,
-				pallet_decl,
-				index,
-				instance,
-				generics,
-			));
-			event_conversions.extend(expand_event_conversion(scrate, pallet_decl, &pallet_event));
-			query_event_part_macros.push(quote! {
-				#path::__substrate_event_check::is_event_part_defined!(#pallet_name);
-			});
-		}
-	}
-
-	Ok(quote! {
-		#( #query_event_part_macros )*
-
-		#[derive(
-			Clone, PartialEq, Eq,
-			#scrate::codec::Encode,
-			#scrate::codec::Decode,
-			#scrate::scale_info::TypeInfo,
-			#scrate::RuntimeDebug,
-		)]
-		#[allow(non_camel_case_types)]
-		pub enum RuntimeEvent {
-			#event_variants
-		}
-
-		#event_conversions
-	})
-}
-
-fn expand_event_variant(
-	runtime: &Ident,
-	pallet: &Pallet,
-	index: u8,
-	instance: Option<&Ident>,
-	generics: &Generics,
-) -> TokenStream {
-	let path = &pallet.path;
-	let variant_name = &pallet.name;
-	let part_is_generic = !generics.params.is_empty();
-	let attr = pallet.cfg_pattern.iter().fold(TokenStream::new(), |acc, pattern| {
-		let attr = TokenStream::from_str(&format!("#[cfg({})]", pattern.original()))
-			.expect("was successfully parsed before; qed");
-		quote! {
-			#acc
-			#attr
-		}
-	});
-
-	match instance {
-		Some(inst) if part_is_generic => quote! {
-			#attr
-			#[codec(index = #index)]
-			#variant_name(#path::Event<#runtime, #path::#inst>),
-		},
-		Some(inst) => quote! {
-			#attr
-			#[codec(index = #index)]
-			#variant_name(#path::Event<#path::#inst>),
-		},
-		None if part_is_generic => quote! {
-			#attr
-			#[codec(index = #index)]
-			#variant_name(#path::Event<#runtime>),
-		},
-		None => quote! {
-			#attr
-			#[codec(index = #index)]
-			#variant_name(#path::Event),
-		},
-	}
-}
-
-fn expand_event_conversion(
-	scrate: &TokenStream,
-	pallet: &Pallet,
-	pallet_event: &TokenStream,
-) -> TokenStream {
-	let variant_name = &pallet.name;
-	let attr = pallet.cfg_pattern.iter().fold(TokenStream::new(), |acc, pattern| {
-		let attr = TokenStream::from_str(&format!("#[cfg({})]", pattern.original()))
-			.expect("was successfully parsed before; qed");
-		quote! {
-			#acc
-			#attr
-		}
-	});
-
-	quote! {
-		#attr
-		impl From<#pallet_event> for RuntimeEvent {
-			fn from(x: #pallet_event) -> Self {
-				RuntimeEvent::#variant_name(x)
-			}
-		}
-		#attr
-		impl TryInto<#pallet_event> for RuntimeEvent {
-			type Error = ();
-
-			fn try_into(self) -> #scrate::sp_std::result::Result<#pallet_event, Self::Error> {
-				match self {
-					Self::#variant_name(evt) => Ok(evt),
-					_ => Err(()),
-				}
-			}
-		}
-	}
-}

substrate/frame/support/procedural/src/construct_runtime/expand/metadata.rs

@@ -15,7 +15,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License
 
-use crate::construct_runtime::Pallet;
+use crate::construct_runtime::{parse::PalletPath, Pallet};
 use proc_macro2::TokenStream;
 use quote::quote;
 use std::str::FromStr;
@@ -26,6 +26,7 @@ pub fn expand_runtime_metadata(
 	pallet_declarations: &[Pallet],
 	scrate: &TokenStream,
 	extrinsic: &TypePath,
+	system_path: &PalletPath,
 ) -> TokenStream {
 	let pallets = pallet_declarations
 		.iter()
@@ -115,6 +116,13 @@ pub fn expand_runtime_metadata(
 					},
 					ty: #scrate::scale_info::meta_type::<#runtime>(),
 					apis: (&rt).runtime_metadata(),
+					outer_enums: #scrate::metadata_ir::OuterEnumsIR {
+						call_enum_ty: #scrate::scale_info::meta_type::<
+								<#runtime as #system_path::Config>::RuntimeCall
+							>(),
+						event_enum_ty: #scrate::scale_info::meta_type::<RuntimeEvent>(),
+						error_enum_ty: #scrate::scale_info::meta_type::<RuntimeError>(),
+					}
 				}
 			}
 

substrate/frame/support/procedural/src/construct_runtime/expand/mod.rs

@@ -17,24 +17,24 @@
 
 mod call;
 mod config;
-mod event;
 mod freeze_reason;
 mod hold_reason;
 mod inherent;
 mod lock_id;
 mod metadata;
 mod origin;
+mod outer_enums;
 mod slash_reason;
 mod unsigned;
 
 pub use call::expand_outer_dispatch;
 pub use config::expand_outer_config;
-pub use event::expand_outer_event;
 pub use freeze_reason::expand_outer_freeze_reason;
 pub use hold_reason::expand_outer_hold_reason;
 pub use inherent::expand_outer_inherent;
 pub use lock_id::expand_outer_lock_id;
 pub use metadata::expand_runtime_metadata;
 pub use origin::expand_outer_origin;
+pub use outer_enums::{expand_outer_enum, OuterEnumType};
 pub use slash_reason::expand_outer_slash_reason;
 pub use unsigned::expand_outer_validate_unsigned;

substrate/frame/support/procedural/src/construct_runtime/expand/outer_enums.rs

@@ -0,0 +1,283 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License
+
+use crate::construct_runtime::Pallet;
+use proc_macro2::{Span, TokenStream};
+use quote::{quote, ToTokens};
+use std::str::FromStr;
+use syn::{Generics, Ident};
+
+/// Represents the types supported for creating an outer enum.
+#[derive(Clone, Copy, PartialEq)]
+pub enum OuterEnumType {
+	/// Collects the Event enums from all pallets.
+	Event,
+	/// Collects the Error enums from all pallets.
+	Error,
+}
+
+impl OuterEnumType {
+	/// The name of the structure this enum represents.
+	fn struct_name(&self) -> &str {
+		match self {
+			OuterEnumType::Event => "RuntimeEvent",
+			OuterEnumType::Error => "RuntimeError",
+		}
+	}
+
+	/// The name of the variant (ie `Event` or `Error`).
+	fn variant_name(&self) -> &str {
+		match self {
+			OuterEnumType::Event => "Event",
+			OuterEnumType::Error => "Error",
+		}
+	}
+}
+
+impl ToTokens for OuterEnumType {
+	fn to_tokens(&self, tokens: &mut TokenStream) {
+		match self {
+			OuterEnumType::Event => quote!(Event).to_tokens(tokens),
+			OuterEnumType::Error => quote!(Error).to_tokens(tokens),
+		}
+	}
+}
+
+/// Create an outer enum that encapsulates all pallets as variants.
+///
+/// Each variant represents a pallet and contains the corresponding type declared with either:
+/// - #[pallet::event] for the [`OuterEnumType::Event`] variant
+/// - #[pallet::error] for the [`OuterEnumType::Error`] variant
+///
+/// The name of the outer enum is prefixed with Runtime, resulting in names like RuntimeEvent
+/// or RuntimeError.
+///
+/// This structure facilitates the decoding process by leveraging the metadata.
+///
+/// # Example
+///
+/// The code generate looks like the following for [`OuterEnumType::Event`].
+///
+/// ```ignore
+/// enum RuntimeEvent {
+///     #[codec(index = 0)]
+///     System(pallet_system::Event),
+///
+///     #[codec(index = 5)]
+///     Balances(pallet_system::Event),
+/// }
+/// ```
+///
+/// Notice that the pallet index is preserved using the `#[codec(index = ..)]` attribute.
+pub fn expand_outer_enum(
+	runtime: &Ident,
+	pallet_decls: &[Pallet],
+	scrate: &TokenStream,
+	enum_ty: OuterEnumType,
+) -> syn::Result<TokenStream> {
+	// Stores all pallet variants.
+	let mut enum_variants = TokenStream::new();
+	// Generates the enum conversion between the `Runtime` outer enum and the pallet's enum.
+	let mut enum_conversions = TokenStream::new();
+	// Specific for events to query via `is_event_part_defined!`.
+	let mut query_enum_part_macros = Vec::new();
+
+	let enum_name_str = enum_ty.variant_name();
+	let enum_name_ident = Ident::new(enum_ty.struct_name(), Span::call_site());
+
+	for pallet_decl in pallet_decls {
+		let Some(pallet_entry) = pallet_decl.find_part(enum_name_str) else {
+			continue
+		};
+
+		let path = &pallet_decl.path;
+		let pallet_name = &pallet_decl.name;
+		let index = pallet_decl.index;
+		let instance = pallet_decl.instance.as_ref();
+		let generics = &pallet_entry.generics;
+
+		if instance.is_some() && generics.params.is_empty() {
+			let msg = format!(
+				"Instantiable pallet with no generic `{}` cannot \
+					be constructed: pallet `{}` must have generic `{}`",
+				enum_name_str, pallet_name, enum_name_str,
+			);
+			return Err(syn::Error::new(pallet_name.span(), msg))
+		}
+
+		let part_is_generic = !generics.params.is_empty();
+		let pallet_enum = match (instance, part_is_generic) {
+			(Some(inst), true) => quote!(#path::#enum_ty::<#runtime, #path::#inst>),
+			(Some(inst), false) => quote!(#path::#enum_ty::<#path::#inst>),
+			(None, true) => quote!(#path::#enum_ty::<#runtime>),
+			(None, false) => quote!(#path::#enum_ty),
+		};
+
+		enum_variants.extend(expand_enum_variant(
+			runtime,
+			pallet_decl,
+			index,
+			instance,
+			generics,
+			enum_ty,
+		));
+		enum_conversions.extend(expand_enum_conversion(
+			scrate,
+			pallet_decl,
+			&pallet_enum,
+			&enum_name_ident,
+		));
+
+		if enum_ty == OuterEnumType::Event {
+			query_enum_part_macros.push(quote! {
+				#path::__substrate_event_check::is_event_part_defined!(#pallet_name);
+			});
+		}
+	}
+
+	// Derives specific for the event.
+	let event_custom_derives =
+		if enum_ty == OuterEnumType::Event { quote!(Clone, PartialEq, Eq,) } else { quote!() };
+
+	// Implementation specific for errors.
+	let error_custom_impl = generate_error_impl(scrate, enum_ty);
+
+	Ok(quote! {
+		#( #query_enum_part_macros )*
+
+		#[derive(
+			#event_custom_derives
+			#scrate::codec::Encode,
+			#scrate::codec::Decode,
+			#scrate::scale_info::TypeInfo,
+			#scrate::RuntimeDebug,
+		)]
+		#[allow(non_camel_case_types)]
+		pub enum #enum_name_ident {
+			#enum_variants
+		}
+
+		#enum_conversions
+
+		#error_custom_impl
+	})
+}
+
+fn expand_enum_variant(
+	runtime: &Ident,
+	pallet: &Pallet,
+	index: u8,
+	instance: Option<&Ident>,
+	generics: &Generics,
+	enum_ty: OuterEnumType,
+) -> TokenStream {
+	let path = &pallet.path;
+	let variant_name = &pallet.name;
+	let part_is_generic = !generics.params.is_empty();
+	let attr = pallet.cfg_pattern.iter().fold(TokenStream::new(), |acc, pattern| {
+		let attr = TokenStream::from_str(&format!("#[cfg({})]", pattern.original()))
+			.expect("was successfully parsed before; qed");
+		quote! {
+			#acc
+			#attr
+		}
+	});
+
+	match instance {
+		Some(inst) if part_is_generic => quote! {
+			#attr
+			#[codec(index = #index)]
+			#variant_name(#path::#enum_ty<#runtime, #path::#inst>),
+		},
+		Some(inst) => quote! {
+			#attr
+			#[codec(index = #index)]
+			#variant_name(#path::#enum_ty<#path::#inst>),
+		},
+		None if part_is_generic => quote! {
+			#attr
+			#[codec(index = #index)]
+			#variant_name(#path::#enum_ty<#runtime>),
+		},
+		None => quote! {
+			#attr
+			#[codec(index = #index)]
+			#variant_name(#path::#enum_ty),
+		},
+	}
+}
+
+fn expand_enum_conversion(
+	scrate: &TokenStream,
+	pallet: &Pallet,
+	pallet_enum: &TokenStream,
+	enum_name_ident: &Ident,
+) -> TokenStream {
+	let variant_name = &pallet.name;
+	let attr = pallet.cfg_pattern.iter().fold(TokenStream::new(), |acc, pattern| {
+		let attr = TokenStream::from_str(&format!("#[cfg({})]", pattern.original()))
+			.expect("was successfully parsed before; qed");
+		quote! {
+			#acc
+			#attr
+		}
+	});
+
+	quote! {
+		#attr
+		impl From<#pallet_enum> for #enum_name_ident {
+			fn from(x: #pallet_enum) -> Self {
+				#enum_name_ident
+				::#variant_name(x)
+			}
+		}
+		#attr
+		impl TryInto<#pallet_enum> for #enum_name_ident {
+			type Error = ();
+
+			fn try_into(self) -> #scrate::sp_std::result::Result<#pallet_enum, Self::Error> {
+				match self {
+					Self::#variant_name(evt) => Ok(evt),
+					_ => Err(()),
+				}
+			}
+		}
+	}
+}
+
+fn generate_error_impl(scrate: &TokenStream, enum_ty: OuterEnumType) -> TokenStream {
+	// Implementation is specific to `Error`s.
+	if enum_ty == OuterEnumType::Event {
+		return quote! {}
+	}
+
+	let enum_name_ident = Ident::new(enum_ty.struct_name(), Span::call_site());
+
+	quote! {
+		impl #enum_name_ident {
+			/// Optionally convert the `DispatchError` into the `RuntimeError`.
+			///
+			/// Returns `Some` if the error matches the `DispatchError::Module` variant, otherwise `None`.
+			pub fn from_dispatch_error(err: #scrate::sp_runtime::DispatchError) -> Option<Self> {
+				let #scrate::sp_runtime::DispatchError::Module(module_error) = err else { return None };
+
+				let bytes = #scrate::codec::Encode::encode(&module_error);
+				#scrate::codec::Decode::decode(&mut &bytes[..]).ok()
+			}
+		}
+	}
+}

substrate/frame/support/procedural/src/construct_runtime/mod.rs

@@ -20,17 +20,69 @@
 //! `construct_runtime` implementation is recursive and can generate code which will call itself in
 //! order to get all the pallet parts for each pallet.
 //!
-//! Pallets define their parts (`Call`, `Storage`, ..) either explicitly with the syntax
-//! `::{Call, ...}` or implicitly.
+//! Pallets can define their parts:
+//!  - Implicitely: `System: frame_system`
+//!  - Explicitly: `System: frame_system::{Pallet, Call}`
 //!
-//! In case a pallet defines its parts implicitly, then the pallet must provide the
-//! `tt_default_parts` macro. `construct_runtime` will generate some code which utilizes `tt_call`
-//! to call the `tt_default_parts` macro of the pallet. `tt_default_parts` will then return the
-//! default pallet parts as input tokens to the `match_and_replace` macro, which ultimately
-//! generates a call to `construct_runtime` again, this time with all the pallet parts explicitly
-//! defined.
+//! The `construct_runtime` transitions from the implicit definition to the explict one.
+//! From the explicit state, Substrate expands the pallets with additional information
+//! that is to be included in the runtime metadata. This expansion makes visible some extra
+//! parts of the pallets, mainly the `Error` if defined. The expanded state looks like
+//! `System: frame_system expanded::{Error} ::{Pallet, Call}` and concatenates the extra expanded
+//! parts with the user-provided parts. For example, the `Pallet`, `Call` and `Error` parts are
+//! collected.
+//!
+//! Pallets must provide the `tt_extra_parts` and `tt_default_parts` macros for these transitions.
+//! These are automatically implemented by the `#[pallet::pallet]` macro.
+//!
+//! This macro also generates the following enums for ease of decoding:
+//!  - `enum RuntimeCall`: This type contains the information needed to decode extrinsics.
+//!  - `enum RuntimeEvent`: This type contains the information needed to decode events.
+//!  - `enum RuntimeError`: While this cannot be used directly to decode `sp_runtime::DispatchError`
+//!    from the chain, it contains the information needed to decode the
+//!    `sp_runtime::DispatchError::Module`.
+//!
+//! # State Transitions
+//!
+//! ```ignore
+//!  +----------+
+//!  | Implicit | -----------+
+//!  +----------+            |
+//!      |                   |
+//!      v                   v
+//!  +----------+     +------------------+
+//!  | Explicit | --> | ExplicitExpanded |
+//!  +----------+     +------------------+
+//! ```
+//!
+//! When all pallet parts are implcit, then the `construct_runtime!` macro expands to its final
+//! state, the `ExplicitExpanded`. Otherwise, all implicit parts are converted to an explicit
+//! expanded part allow the `construct_runtime!` to expand any remaining explicit parts to an
+//! explicit expanded part.
+//!
+//! # Implicit to Explicit
+//!
+//! The `construct_runtime` macro transforms the implicit declaration of each pallet
+//! `System: frame_system` to an explicit one `System: frame_system::{Pallet, Call}` using the
+//! `tt_default_parts` macro.
+//!
+//! The `tt_default_parts` macro exposes a comma separated list of pallet parts. For example, the
+//! `Event` part is exposed only if the pallet implements an event via `#[pallet::event]` macro.
+//! The tokens generated by this macro are ` expanded :: { Pallet, Call }` for our example.
+//!
+//! The `match_and_insert` macro takes in 3 arguments:
+//!  - target: This is the `TokenStream` that contains the `construct_runtime!` macro.
+//!  - pattern: The pattern to match against in the target stream.
+//!  - tokens: The tokens to added after the pattern match.
+//!
+//! The `construct_runtime` macro uses the `tt_call` to get the default pallet parts via
+//! the `tt_default_parts` macro defined by each pallet. The pallet parts are then returned as
+//! input to the `match_and_replace` macro.
+//! The `match_and_replace` then will modify the the `construct_runtime!` to expand the implicit
+//! definition to the explicit one.
+//!
+//! For example,
 //!
-//! E.g.
 //! ```ignore
 //! construct_runtime!(
 //! 	//...
@@ -106,6 +158,7 @@
 //! 	tokens = [{ ::{Pallet, Call} }]
 //! }
 //! ```
+//!
 //! Which will then finally expand to the following:
 //! ```ignore
 //! construct_runtime!(
@@ -116,6 +169,7 @@
 //! 	}
 //! )
 //! ```
+//!
 //! This call has no implicit pallet parts, thus it will expand to the runtime construction:
 //! ```ignore
 //! pub struct Runtime { ... }
@@ -140,6 +194,19 @@
 //!     |  w/ pallet parts   |
 //!     +--------------------+
 //! ```
+//!
+//! # Explicit to Explicit Expanded
+//!
+//! Users normally do not care about this transition.
+//!
+//! Similarly to the previous transition, the macro expansion transforms `System:
+//! frame_system::{Pallet, Call}` into  `System: frame_system expanded::{Error} ::{Pallet, Call}`.
+//! The `expanded` section adds extra parts that the Substrate would like to expose for each pallet
+//! by default. This is done to expose the approprite types for metadata construction.
+//!
+//! This time, instead of calling `tt_default_parts` we are using the `tt_extra_parts` macro.
+//! This macro returns the ` :: expanded { Error }` list of additional parts we would like to
+//! expose.
 
 mod expand;
 mod parse;
@@ -171,9 +238,16 @@ pub fn construct_runtime(input: TokenStream) -> TokenStream {
 	let res = match definition {
 		RuntimeDeclaration::Implicit(implicit_def) =>
 			check_pallet_number(input_copy.clone().into(), implicit_def.pallets.len()).and_then(
-				|_| construct_runtime_intermediary_expansion(input_copy.into(), implicit_def),
+				|_| construct_runtime_implicit_to_explicit(input_copy.into(), implicit_def),
 			),
-		RuntimeDeclaration::Explicit(explicit_decl) =>
+		RuntimeDeclaration::Explicit(explicit_decl) => check_pallet_number(
+			input_copy.clone().into(),
+			explicit_decl.pallets.len(),
+		)
+		.and_then(|_| {
+			construct_runtime_explicit_to_explicit_expanded(input_copy.into(), explicit_decl)
+		}),
+		RuntimeDeclaration::ExplicitExpanded(explicit_decl) =>
 			check_pallet_number(input_copy.into(), explicit_decl.pallets.len())
 				.and_then(|_| construct_runtime_final_expansion(explicit_decl)),
 	};
@@ -189,9 +263,14 @@ pub fn construct_runtime(input: TokenStream) -> TokenStream {
 	res.into()
 }
 
-/// When some pallet have implicit parts definition then the macro will expand into a macro call to
-/// `construct_runtime_args` of each pallets, see root documentation.
-fn construct_runtime_intermediary_expansion(
+/// All pallets that have implicit pallet parts (ie `System: frame_system`) are
+/// expanded with the default parts defined by the pallet's `tt_default_parts` macro.
+///
+/// This function transforms the [`RuntimeDeclaration::Implicit`] into
+/// [`RuntimeDeclaration::Explicit`] that is not yet fully expanded.
+///
+/// For more details, please refer to the root documentation.
+fn construct_runtime_implicit_to_explicit(
 	input: TokenStream2,
 	definition: ImplicitRuntimeDeclaration,
 ) -> Result<TokenStream2> {
@@ -218,6 +297,42 @@ fn construct_runtime_intermediary_expansion(
 	Ok(expansion)
 }
 
+/// All pallets that have
+///   (I): explicit pallet parts (ie `System: frame_system::{Pallet, Call}`) and
+///   (II): are not fully expanded (ie do not include the `Error` expansion part)
+/// are fully expanded by including the parts from the pallet's `tt_extra_parts` macro.
+///
+/// This function transforms the [`RuntimeDeclaration::Explicit`] that is not yet fully expanded
+/// into [`RuntimeDeclaration::ExplicitExpanded`] fully expanded.
+///
+/// For more details, please refer to the root documentation.
+fn construct_runtime_explicit_to_explicit_expanded(
+	input: TokenStream2,
+	definition: ExplicitRuntimeDeclaration,
+) -> Result<TokenStream2> {
+	let frame_support = generate_crate_access_2018("frame-support")?;
+	let mut expansion = quote::quote!(
+		#frame_support::construct_runtime! { #input }
+	);
+	for pallet in definition.pallets.iter().filter(|pallet| !pallet.is_expanded) {
+		let pallet_path = &pallet.path;
+		let pallet_name = &pallet.name;
+		let pallet_instance = pallet.instance.as_ref().map(|instance| quote::quote!(::<#instance>));
+		expansion = quote::quote!(
+			#frame_support::tt_call! {
+				macro = [{ #pallet_path::tt_extra_parts }]
+				frame_support = [{ #frame_support }]
+				~~> #frame_support::match_and_insert! {
+					target = [{ #expansion }]
+					pattern = [{ #pallet_name: #pallet_path #pallet_instance }]
+				}
+			}
+		);
+	}
+
+	Ok(expansion)
+}
+
 /// All pallets have explicit definition of parts, this will expand to the runtime declaration.
 fn construct_runtime_final_expansion(
 	definition: ExplicitRuntimeDeclaration,
@@ -264,14 +379,23 @@ fn construct_runtime_final_expansion(
 	let scrate = generate_crate_access(hidden_crate_name, "frame-support");
 	let scrate_decl = generate_hidden_includes(hidden_crate_name, "frame-support");
 
-	let outer_event = expand::expand_outer_event(&name, &pallets, &scrate)?;
+	let outer_event =
+		expand::expand_outer_enum(&name, &pallets, &scrate, expand::OuterEnumType::Event)?;
+	let outer_error =
+		expand::expand_outer_enum(&name, &pallets, &scrate, expand::OuterEnumType::Error)?;
 
 	let outer_origin = expand::expand_outer_origin(&name, system_pallet, &pallets, &scrate)?;
 	let all_pallets = decl_all_pallets(&name, pallets.iter(), &features);
 	let pallet_to_index = decl_pallet_runtime_setup(&name, &pallets, &scrate);
 
 	let dispatch = expand::expand_outer_dispatch(&name, system_pallet, &pallets, &scrate);
-	let metadata = expand::expand_runtime_metadata(&name, &pallets, &scrate, &unchecked_extrinsic);
+	let metadata = expand::expand_runtime_metadata(
+		&name,
+		&pallets,
+		&scrate,
+		&unchecked_extrinsic,
+		&system_pallet.path,
+	);
 	let outer_config = expand::expand_outer_config(&name, &pallets, &scrate);
 	let inherent =
 		expand::expand_outer_inherent(&name, &block, &unchecked_extrinsic, &pallets, &scrate);
@@ -331,6 +455,8 @@ fn construct_runtime_final_expansion(
 
 		#outer_event
 
+		#outer_error
+
 		#outer_origin
 
 		#all_pallets

substrate/frame/support/procedural/src/construct_runtime/parse.rs

@@ -35,6 +35,7 @@ mod keyword {
 	syn::custom_keyword!(Call);
 	syn::custom_keyword!(Storage);
 	syn::custom_keyword!(Event);
+	syn::custom_keyword!(Error);
 	syn::custom_keyword!(Config);
 	syn::custom_keyword!(Origin);
 	syn::custom_keyword!(Inherent);
@@ -45,6 +46,7 @@ mod keyword {
 	syn::custom_keyword!(SlashReason);
 	syn::custom_keyword!(exclude_parts);
 	syn::custom_keyword!(use_parts);
+	syn::custom_keyword!(expanded);
 }
 
 /// Declaration of a runtime.
@@ -56,6 +58,7 @@ mod keyword {
 pub enum RuntimeDeclaration {
 	Implicit(ImplicitRuntimeDeclaration),
 	Explicit(ExplicitRuntimeDeclaration),
+	ExplicitExpanded(ExplicitRuntimeDeclaration),
 }
 
 /// Declaration of a runtime with some pallet with implicit declaration of parts.
@@ -106,6 +109,13 @@ impl Parse for RuntimeDeclaration {
 					pallets,
 					pallets_token,
 				})),
+			PalletsConversion::ExplicitExpanded(pallets) =>
+				Ok(RuntimeDeclaration::ExplicitExpanded(ExplicitRuntimeDeclaration {
+					name,
+					where_section,
+					pallets,
+					pallets_token,
+				})),
 		}
 	}
 }
@@ -188,6 +198,8 @@ impl Parse for WhereDefinition {
 /// The declaration of a pallet.
 #[derive(Debug, Clone)]
 pub struct PalletDeclaration {
+	/// Is this pallet fully expanded?
+	pub is_expanded: bool,
 	/// The name of the pallet, e.g.`System` in `System: frame_system`.
 	pub name: Ident,
 	/// Optional attributes tagged right above a pallet declaration.
@@ -233,6 +245,7 @@ impl Parse for PalletDeclaration {
 			let _: Token![>] = input.parse()?;
 			res
 		} else if !(input.peek(Token![::]) && input.peek3(token::Brace)) &&
+			!input.peek(keyword::expanded) &&
 			!input.peek(keyword::exclude_parts) &&
 			!input.peek(keyword::use_parts) &&
 			!input.peek(Token![=]) &&
@@ -246,10 +259,21 @@ impl Parse for PalletDeclaration {
 			None
 		};
 
+		// Check if the pallet is fully expanded.
+		let (is_expanded, extra_parts) = if input.peek(keyword::expanded) {
+			let _: keyword::expanded = input.parse()?;
+			let _: Token![::] = input.parse()?;
+			(true, parse_pallet_parts(input)?)
+		} else {
+			(false, vec![])
+		};
+
 		// Parse for explicit parts
 		let pallet_parts = if input.peek(Token![::]) && input.peek3(token::Brace) {
 			let _: Token![::] = input.parse()?;
-			Some(parse_pallet_parts(input)?)
+			let mut parts = parse_pallet_parts(input)?;
+			parts.extend(extra_parts.into_iter());
+			Some(parts)
 		} else if !input.peek(keyword::exclude_parts) &&
 			!input.peek(keyword::use_parts) &&
 			!input.peek(Token![=]) &&
@@ -260,7 +284,7 @@ impl Parse for PalletDeclaration {
 				"Unexpected tokens, expected one of `::{`, `exclude_parts`, `use_parts`, `=`, `,`",
 			))
 		} else {
-			None
+			is_expanded.then_some(extra_parts)
 		};
 
 		// Parse for specified parts
@@ -288,7 +312,7 @@ impl Parse for PalletDeclaration {
 			None
 		};
 
-		Ok(Self { attrs, name, path, instance, pallet_parts, specified_parts, index })
+		Ok(Self { is_expanded, attrs, name, path, instance, pallet_parts, specified_parts, index })
 	}
 }
 
@@ -371,6 +395,7 @@ pub enum PalletPartKeyword {
 	Call(keyword::Call),
 	Storage(keyword::Storage),
 	Event(keyword::Event),
+	Error(keyword::Error),
 	Config(keyword::Config),
 	Origin(keyword::Origin),
 	Inherent(keyword::Inherent),
@@ -393,6 +418,8 @@ impl Parse for PalletPartKeyword {
 			Ok(Self::Storage(input.parse()?))
 		} else if lookahead.peek(keyword::Event) {
 			Ok(Self::Event(input.parse()?))
+		} else if lookahead.peek(keyword::Error) {
+			Ok(Self::Error(input.parse()?))
 		} else if lookahead.peek(keyword::Config) {
 			Ok(Self::Config(input.parse()?))
 		} else if lookahead.peek(keyword::Origin) {
@@ -423,6 +450,7 @@ impl PalletPartKeyword {
 			Self::Call(_) => "Call",
 			Self::Storage(_) => "Storage",
 			Self::Event(_) => "Event",
+			Self::Error(_) => "Error",
 			Self::Config(_) => "Config",
 			Self::Origin(_) => "Origin",
 			Self::Inherent(_) => "Inherent",
@@ -441,7 +469,7 @@ impl PalletPartKeyword {
 
 	/// Returns the names of all pallet parts that allow to have a generic argument.
 	fn all_generic_arg() -> &'static [&'static str] {
-		&["Event", "Origin", "Config"]
+		&["Event", "Error", "Origin", "Config"]
 	}
 }
 
@@ -452,6 +480,7 @@ impl ToTokens for PalletPartKeyword {
 			Self::Call(inner) => inner.to_tokens(tokens),
 			Self::Storage(inner) => inner.to_tokens(tokens),
 			Self::Event(inner) => inner.to_tokens(tokens),
+			Self::Error(inner) => inner.to_tokens(tokens),
 			Self::Config(inner) => inner.to_tokens(tokens),
 			Self::Origin(inner) => inner.to_tokens(tokens),
 			Self::Inherent(inner) => inner.to_tokens(tokens),
@@ -554,6 +583,8 @@ fn parse_pallet_parts_no_generic(input: ParseStream) -> Result<Vec<PalletPartNoG
 /// The final definition of a pallet with the resulting fixed index and explicit parts.
 #[derive(Debug, Clone)]
 pub struct Pallet {
+	/// Is this pallet fully expanded?
+	pub is_expanded: bool,
 	/// The name of the pallet, e.g.`System` in `System: frame_system`.
 	pub name: Ident,
 	/// Either automatically infered, or defined (e.g. `MyPallet ...  = 3,`).
@@ -586,9 +617,35 @@ impl Pallet {
 }
 
 /// Result of a conversion of a declaration of pallets.
+///
+/// # State Transitions
+///
+/// ```ignore
+/// +----------+    +----------+    +------------------+
+/// | Implicit | -> | Explicit | -> | ExplicitExpanded |
+/// +----------+    +----------+    +------------------+
+/// ```
 enum PalletsConversion {
+	/// Pallets implicitely declare parts.
+	///
+	/// `System: frame_system`.
 	Implicit(Vec<PalletDeclaration>),
+	/// Pallets explicitly declare parts.
+	///
+	/// `System: frame_system::{Pallet, Call}`
+	///
+	/// However, for backwards compatibility with Polkadot/Kusama
+	/// we must propagate some other parts to the pallet by default.
 	Explicit(Vec<Pallet>),
+	/// Pallets explicitly declare parts that are fully expanded.
+	///
+	/// This is the end state that contains extra parts included by
+	/// default by Subtrate.
+	///
+	/// `System: frame_system expanded::{Error} ::{Pallet, Call}`
+	///
+	/// For this example, the `Pallet`, `Call` and `Error` parts are collected.
+	ExplicitExpanded(Vec<Pallet>),
 }
 
 /// Convert from the parsed pallet declaration to their final information.
@@ -604,6 +661,7 @@ fn convert_pallets(pallets: Vec<PalletDeclaration>) -> syn::Result<PalletsConver
 	let mut indices = HashMap::new();
 	let mut last_index: Option<u8> = None;
 	let mut names = HashMap::new();
+	let mut is_expanded = true;
 
 	let pallets = pallets
 		.into_iter()
@@ -698,7 +756,10 @@ fn convert_pallets(pallets: Vec<PalletDeclaration>) -> syn::Result<PalletsConver
 				})
 				.collect::<Result<Vec<_>>>()?;
 
+			is_expanded &= pallet.is_expanded;
+
 			Ok(Pallet {
+				is_expanded: pallet.is_expanded,
 				name: pallet.name,
 				index: final_index,
 				path: pallet.path,
@@ -709,5 +770,9 @@ fn convert_pallets(pallets: Vec<PalletDeclaration>) -> syn::Result<PalletsConver
 		})
 		.collect::<Result<Vec<_>>>()?;
 
-	Ok(PalletsConversion::Explicit(pallets))
+	if is_expanded {
+		Ok(PalletsConversion::ExplicitExpanded(pallets))
+	} else {
+		Ok(PalletsConversion::Explicit(pallets))
+	}
 }

substrate/frame/support/procedural/src/pallet/expand/tt_default_parts.rs

@@ -26,6 +26,8 @@ pub fn expand_tt_default_parts(def: &mut Def) -> proc_macro2::TokenStream {
 	let count = COUNTER.with(|counter| counter.borrow_mut().inc());
 	let default_parts_unique_id =
 		syn::Ident::new(&format!("__tt_default_parts_{}", count), def.item.span());
+	let extra_parts_unique_id =
+		syn::Ident::new(&format!("__tt_extra_parts_{}", count), def.item.span());
 
 	let call_part = def.call.as_ref().map(|_| quote::quote!(Call,));
 
@@ -36,6 +38,8 @@ pub fn expand_tt_default_parts(def: &mut Def) -> proc_macro2::TokenStream {
 		quote::quote!( Event #gen , )
 	});
 
+	let error_part = def.error.as_ref().map(|_| quote::quote!(Error<T>,));
+
 	let origin_part = def.origin.as_ref().map(|origin| {
 		let gen = origin.is_generic.then(|| quote::quote!( <T> ));
 		quote::quote!( Origin #gen , )
@@ -95,8 +99,8 @@ pub fn expand_tt_default_parts(def: &mut Def) -> proc_macro2::TokenStream {
 				$($frame_support)*::tt_return! {
 					$caller
 					tokens = [{
-						::{
-							Pallet, #call_part #storage_part #event_part #origin_part #config_part
+						expanded::{
+							Pallet, #call_part #storage_part #event_part #error_part #origin_part #config_part
 							#inherent_part #validate_unsigned_part #freeze_reason_part
 							#hold_reason_part #lock_id_part #slash_reason_part
 						}
@@ -106,5 +110,33 @@ pub fn expand_tt_default_parts(def: &mut Def) -> proc_macro2::TokenStream {
 		}
 
 		pub use #default_parts_unique_id as tt_default_parts;
+
+
+		// This macro is similar to the `tt_default_parts!`. It expands the pallets thare are declared
+		// explicitly (`System: frame_system::{Pallet, Call}`) with extra parts.
+		//
+		// For example, after expansion an explicit pallet would look like:
+		// `System: expanded::{Error} ::{Pallet, Call}`.
+		//
+		// The `expanded` keyword is a marker of the final state of the `construct_runtime!`.
+		#[macro_export]
+		#[doc(hidden)]
+		macro_rules! #extra_parts_unique_id {
+			{
+				$caller:tt
+				frame_support = [{ $($frame_support:ident)::* }]
+			} => {
+				$($frame_support)*::tt_return! {
+					$caller
+					tokens = [{
+						expanded::{
+							#error_part
+						}
+					}]
+				}
+			};
+		}
+
+		pub use #extra_parts_unique_id as tt_extra_parts;
 	)
 }

substrate/frame/support/test/tests/common/mod.rs

@@ -0,0 +1,19 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+///! Common functionality between tests.
+pub mod outer_enums;

substrate/frame/support/test/tests/common/outer_enums.rs

@@ -0,0 +1,146 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Create 3 pallets for testing the outer error enum construction:
+//
+// - `pallet`: declares an error with `#[pallet::error]`
+// - `pallet2`: declares an error with `#[pallet::error]`
+// - `pallet3`: does not declare an error.
+
+#[frame_support::pallet(dev_mode)]
+pub mod pallet {
+	use frame_support::pallet_prelude::*;
+
+	#[pallet::config]
+	pub trait Config<I: 'static = ()>: frame_system::Config {
+		type RuntimeEvent: From<Event<Self, I>>
+			+ IsType<<Self as frame_system::Config>::RuntimeEvent>;
+	}
+
+	#[pallet::event]
+	pub enum Event<T: Config<I>, I: 'static = ()> {
+		/// Something
+		Something(u32),
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T, I = ()>(PhantomData<(T, I)>);
+
+	#[pallet::genesis_config]
+	pub struct GenesisConfig<T: Config<I>, I: 'static = ()> {
+		phantom: PhantomData<(T, I)>,
+	}
+
+	impl<T: Config<I>, I: 'static> Default for GenesisConfig<T, I> {
+		fn default() -> Self {
+			GenesisConfig { phantom: Default::default() }
+		}
+	}
+
+	#[pallet::genesis_build]
+	impl<T: Config<I>, I: 'static> GenesisBuild<T, I> for GenesisConfig<T, I> {
+		fn build(&self) {}
+	}
+
+	#[pallet::error]
+	#[derive(PartialEq, Eq)]
+	pub enum Error<T, I = ()> {
+		/// doc comment put into metadata
+		InsufficientProposersBalance,
+		NonExistentStorageValue,
+	}
+}
+
+#[frame_support::pallet]
+pub mod pallet2 {
+	use frame_support::pallet_prelude::*;
+
+	#[pallet::config]
+	pub trait Config<I: 'static = ()>: frame_system::Config {
+		type RuntimeEvent: From<Event<Self, I>>
+			+ IsType<<Self as frame_system::Config>::RuntimeEvent>;
+	}
+
+	#[pallet::event]
+	pub enum Event<T: Config<I>, I: 'static = ()> {
+		/// Something
+		Something(u32),
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T, I = ()>(PhantomData<(T, I)>);
+
+	#[pallet::genesis_config]
+	pub struct GenesisConfig<T: Config<I>, I: 'static = ()> {
+		phantom: PhantomData<(T, I)>,
+	}
+
+	impl<T: Config<I>, I: 'static> Default for GenesisConfig<T, I> {
+		fn default() -> Self {
+			GenesisConfig { phantom: Default::default() }
+		}
+	}
+
+	#[pallet::genesis_build]
+	impl<T: Config<I>, I: 'static> GenesisBuild<T, I> for GenesisConfig<T, I> {
+		fn build(&self) {}
+	}
+
+	#[pallet::error]
+	#[derive(PartialEq, Eq)]
+	pub enum Error<T, I = ()> {
+		/// doc comment put into metadata
+		OtherInsufficientProposersBalance,
+		OtherNonExistentStorageValue,
+	}
+}
+
+#[frame_support::pallet]
+pub mod pallet3 {
+	use frame_support::pallet_prelude::*;
+
+	#[pallet::config]
+	pub trait Config<I: 'static = ()>: frame_system::Config {
+		type RuntimeEvent: From<Event<Self, I>>
+			+ IsType<<Self as frame_system::Config>::RuntimeEvent>;
+	}
+
+	#[pallet::event]
+	pub enum Event<T: Config<I>, I: 'static = ()> {
+		/// Something
+		Something(u32),
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T, I = ()>(PhantomData<(T, I)>);
+
+	#[pallet::genesis_config]
+	pub struct GenesisConfig<T: Config<I>, I: 'static = ()> {
+		phantom: PhantomData<(T, I)>,
+	}
+
+	impl<T: Config<I>, I: 'static> Default for GenesisConfig<T, I> {
+		fn default() -> Self {
+			GenesisConfig { phantom: Default::default() }
+		}
+	}
+
+	#[pallet::genesis_build]
+	impl<T: Config<I>, I: 'static> GenesisBuild<T, I> for GenesisConfig<T, I> {
+		fn build(&self) {}
+	}
+}

substrate/frame/support/test/tests/construct_runtime_ui/generics_in_invalid_module.stderr

@@ -1,4 +1,4 @@
-error: `Call` is not allowed to have generics. Only the following pallets are allowed to have generics: `Event`, `Origin`, `Config`.
+error: `Call` is not allowed to have generics. Only the following pallets are allowed to have generics: `Event`, `Error`, `Origin`, `Config`.
   --> $DIR/generics_in_invalid_module.rs:10:36
    |
 10 |         Balance: balances::<Instance1>::{Call<T>, Origin<T>},

substrate/frame/support/test/tests/construct_runtime_ui/invalid_module_details_keyword.stderr

@@ -1,4 +1,4 @@
-error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`
+error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Error`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`
  --> $DIR/invalid_module_details_keyword.rs:9:20
   |
 9 |         system: System::{enum},

substrate/frame/support/test/tests/construct_runtime_ui/invalid_module_entry.rs

@@ -7,7 +7,7 @@ construct_runtime! {
 		UncheckedExtrinsic = UncheckedExtrinsic
 	{
 		System: system::{Pallet},
-		Balance: balances::{Error},
+		Balance: balances::{Unexpected},
 	}
 }
 

substrate/frame/support/test/tests/construct_runtime_ui/invalid_module_entry.stderr

@@ -1,5 +1,5 @@
-error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`
+error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Error`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`
   --> $DIR/invalid_module_entry.rs:10:23
    |
-10 |         Balance: balances::{Error},
-   |                             ^^^^^
+10 |         Balance: balances::{Unexpected},
+   |                             ^^^^^^^^^^

substrate/frame/support/test/tests/construct_runtime_ui/missing_event_generic_on_module_with_instance.rs

@@ -6,8 +6,8 @@ construct_runtime! {
 		NodeBlock = Block,
 		UncheckedExtrinsic = UncheckedExtrinsic
 	{
-		System: system::{Pallet},
-		Balance: balances::<Instance1>::{Event},
+		System: system expanded::{}::{Pallet},
+		Balance: balances::<Instance1> expanded::{}::{Event},
 	}
 }
 

substrate/frame/support/test/tests/construct_runtime_ui/missing_event_generic_on_module_with_instance.stderr

@@ -1,5 +1,5 @@
 error: Instantiable pallet with no generic `Event` cannot be constructed: pallet `Balance` must have generic `Event`
   --> $DIR/missing_event_generic_on_module_with_instance.rs:10:3
    |
-10 |         Balance: balances::<Instance1>::{Event},
+10 |         Balance: balances::<Instance1> expanded::{}::{Event},
    |         ^^^^^^^

substrate/frame/support/test/tests/construct_runtime_ui/missing_origin_generic_on_module_with_instance.rs

@@ -6,8 +6,8 @@ construct_runtime! {
 		NodeBlock = Block,
 		UncheckedExtrinsic = UncheckedExtrinsic
 	{
-		System: system::{Pallet},
-		Balance: balances::<Instance1>::{Origin},
+		System: system expanded::{}::{Pallet},
+		Balance: balances::<Instance1> expanded::{}::{Origin},
 	}
 }
 

substrate/frame/support/test/tests/construct_runtime_ui/missing_origin_generic_on_module_with_instance.stderr

@@ -1,5 +1,5 @@
 error: Instantiable pallet with no generic `Origin` cannot be constructed: pallet `Balance` must have generic `Origin`
   --> $DIR/missing_origin_generic_on_module_with_instance.rs:10:3
    |
-10 |         Balance: balances::<Instance1>::{Origin},
+10 |         Balance: balances::<Instance1> expanded::{}::{Origin},
    |         ^^^^^^^

substrate/frame/support/test/tests/construct_runtime_ui/undefined_event_part.rs

@@ -52,8 +52,8 @@ construct_runtime! {
 		NodeBlock = Block,
 		UncheckedExtrinsic = UncheckedExtrinsic
 	{
-		System: frame_system::{Pallet, Call, Storage, Config, Event<T>},
-		Pallet: pallet::{Pallet, Event},
+		System: frame_system expanded::{}::{Pallet, Call, Storage, Config, Event<T>},
+		Pallet: pallet expanded::{}::{Pallet, Event},
 	}
 }
 

substrate/frame/support/test/tests/construct_runtime_ui/undefined_genesis_config_part.rs

@@ -52,8 +52,8 @@ construct_runtime! {
 		NodeBlock = Block,
 		UncheckedExtrinsic = UncheckedExtrinsic
 	{
-		System: frame_system::{Pallet, Call, Storage, Config, Event<T>},
-		Pallet: pallet::{Pallet, Config},
+		System: frame_system expanded::{}::{Pallet, Call, Storage, Config, Event<T>},
+		Pallet: pallet expanded::{}::{Pallet, Config},
 	}
 }
 

substrate/frame/support/test/tests/construct_runtime_ui/undefined_inherent_part.rs

@@ -52,8 +52,8 @@ construct_runtime! {
 		NodeBlock = Block,
 		UncheckedExtrinsic = UncheckedExtrinsic
 	{
-		System: frame_system::{Pallet, Call, Storage, Config, Event<T>},
-		Pallet: pallet::{Pallet, Inherent},
+		System: frame_system expanded::{}::{Pallet, Call, Storage, Config, Event<T>},
+		Pallet: pallet expanded::{}::{Pallet, Inherent},
 	}
 }
 

substrate/frame/support/test/tests/construct_runtime_ui/undefined_origin_part.rs

@@ -52,8 +52,8 @@ construct_runtime! {
 		NodeBlock = Block,
 		UncheckedExtrinsic = UncheckedExtrinsic
 	{
-		System: frame_system::{Pallet, Call, Storage, Config, Event<T>},
-		Pallet: pallet::{Pallet, Origin},
+		System: frame_system expanded::{}::{Pallet, Call, Storage, Config, Event<T>},
+		Pallet: pallet expanded::{}::{Pallet, Origin},
 	}
 }
 

substrate/frame/support/test/tests/construct_runtime_ui/undefined_validate_unsigned_part.rs

@@ -1,6 +1,6 @@
 use frame_support::construct_runtime;
-use sp_runtime::{generic, traits::BlakeTwo256};
 use sp_core::sr25519;
+use sp_runtime::{generic, traits::BlakeTwo256};
 
 #[frame_support::pallet]
 mod pallet {

substrate/frame/support/test/tests/construct_runtime_ui/undefined_validate_unsigned_part.stderr

@@ -28,50 +28,54 @@ error[E0599]: no variant or associated item named `Pallet` found for enum `Runti
    | ||        -^^^^^^ variant or associated item not found in `RuntimeCall`
    | ||________|
    | |
-57 | |      }
-58 | |  }
-   | |__- variant or associated item `Pallet` not found for this enum
+...  |
 
 error[E0599]: no function or associated item named `pre_dispatch` found for struct `pallet::Pallet` in the current scope
   --> tests/construct_runtime_ui/undefined_validate_unsigned_part.rs:49:1
    |
-11 |       pub struct Pallet<T>(_);
-   |       -------------------- function or associated item `pre_dispatch` not found for this struct
+11 |        pub struct Pallet<T>(_);
+   |        -------------------- function or associated item `pre_dispatch` not found for this struct
 ...
-49 |   construct_runtime! {
-   |  _^
-50 | |     pub struct Runtime where
-51 | |         Block = Block,
-52 | |         NodeBlock = Block,
+49 |    construct_runtime! {
+   |  __^
+   | | _|
+   | ||
+50 | ||     pub struct Runtime where
+51 | ||         Block = Block,
+52 | ||         NodeBlock = Block,
+...  ||
+57 | ||     }
+58 | || }
+   | ||_- in this macro invocation
 ...  |
-57 | |     }
-58 | | }
-   | |_^ function or associated item not found in `Pallet<Runtime>`
    |
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following traits define an item `pre_dispatch`, perhaps you need to implement one of them:
            candidate #1: `SignedExtension`
            candidate #2: `ValidateUnsigned`
-   = note: this error originates in the macro `construct_runtime` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `frame_support::construct_runtime` which comes from the expansion of the macro `construct_runtime` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0599]: no function or associated item named `validate_unsigned` found for struct `pallet::Pallet` in the current scope
   --> tests/construct_runtime_ui/undefined_validate_unsigned_part.rs:49:1
    |
-11 |       pub struct Pallet<T>(_);
-   |       -------------------- function or associated item `validate_unsigned` not found for this struct
+11 |        pub struct Pallet<T>(_);
+   |        -------------------- function or associated item `validate_unsigned` not found for this struct
 ...
-49 |   construct_runtime! {
-   |  _^
-50 | |     pub struct Runtime where
-51 | |         Block = Block,
-52 | |         NodeBlock = Block,
+49 |    construct_runtime! {
+   |  __^
+   | | _|
+   | ||
+50 | ||     pub struct Runtime where
+51 | ||         Block = Block,
+52 | ||         NodeBlock = Block,
+...  ||
+57 | ||     }
+58 | || }
+   | ||_- in this macro invocation
 ...  |
-57 | |     }
-58 | | }
-   | |_^ function or associated item not found in `Pallet<Runtime>`
    |
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following traits define an item `validate_unsigned`, perhaps you need to implement one of them:
            candidate #1: `SignedExtension`
            candidate #2: `ValidateUnsigned`
-   = note: this error originates in the macro `construct_runtime` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `frame_support::construct_runtime` which comes from the expansion of the macro `construct_runtime` (in Nightly builds, run with -Z macro-backtrace for more info)

substrate/frame/support/test/tests/pallet_instance.rs

@@ -419,6 +419,39 @@ fn error_expand() {
 	);
 }
 
+#[test]
+fn module_error_outer_enum_expand() {
+	// assert that all variants of the Example pallet are included into the
+	// RuntimeError definition.
+	match RuntimeError::Example(pallet::Error::InsufficientProposersBalance) {
+		RuntimeError::Example(example) => match example {
+			pallet::Error::InsufficientProposersBalance => (),
+			pallet::Error::NonExistentStorageValue => (),
+			// Extra pattern added by `construct_runtime`.
+			pallet::Error::__Ignore(_, _) => (),
+		},
+		_ => (),
+	};
+}
+
+#[test]
+fn module_error_from_dispatch_error() {
+	let dispatch_err = DispatchError::Module(ModuleError {
+		index: 1,
+		error: [0; 4],
+		message: Some("InsufficientProposersBalance"),
+	});
+	let err = RuntimeError::from_dispatch_error(dispatch_err).unwrap();
+
+	match err {
+		RuntimeError::Example(pallet::Error::InsufficientProposersBalance) => (),
+		_ => panic!("Module error constructed incorrectly"),
+	};
+
+	// Only `ModuleError` is converted.
+	assert!(RuntimeError::from_dispatch_error(DispatchError::BadOrigin).is_none());
+}
+
 #[test]
 fn instance_expand() {
 	// assert same type

substrate/frame/support/test/tests/pallet_outer_enums_explicit.rs

@@ -0,0 +1,140 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use frame_support::traits::ConstU32;
+
+mod common;
+
+use common::outer_enums::{pallet, pallet2};
+
+pub type Header = sp_runtime::generic::Header<u32, sp_runtime::traits::BlakeTwo256>;
+pub type Block = sp_runtime::generic::Block<Header, UncheckedExtrinsic>;
+pub type UncheckedExtrinsic = sp_runtime::generic::UncheckedExtrinsic<u32, RuntimeCall, (), ()>;
+
+impl frame_system::Config for Runtime {
+	type BaseCallFilter = frame_support::traits::Everything;
+	type RuntimeOrigin = RuntimeOrigin;
+	type Index = u64;
+	type BlockNumber = u32;
+	type RuntimeCall = RuntimeCall;
+	type Hash = sp_runtime::testing::H256;
+	type Hashing = sp_runtime::traits::BlakeTwo256;
+	type AccountId = u64;
+	type Lookup = sp_runtime::traits::IdentityLookup<Self::AccountId>;
+	type Header = Header;
+	type RuntimeEvent = RuntimeEvent;
+	type BlockHashCount = ConstU32<250>;
+	type BlockWeights = ();
+	type BlockLength = ();
+	type DbWeight = ();
+	type Version = ();
+	type PalletInfo = PalletInfo;
+	type AccountData = ();
+	type OnNewAccount = ();
+	type OnKilledAccount = ();
+	type SystemWeightInfo = ();
+	type SS58Prefix = ();
+	type OnSetCode = ();
+	type MaxConsumers = ConstU32<16>;
+}
+
+impl common::outer_enums::pallet::Config for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet::Config<common::outer_enums::pallet::Instance1> for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet2::Config for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet2::Config<common::outer_enums::pallet::Instance1> for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet3::Config for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet3::Config<common::outer_enums::pallet::Instance1> for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+
+frame_support::construct_runtime!(
+	pub struct Runtime where
+		Block = Block,
+		NodeBlock = Block,
+		UncheckedExtrinsic = UncheckedExtrinsic
+	{
+		// Exclude part `Storage` in order not to check its metadata in tests.
+		System: frame_system::{Pallet, Config, Call, Event<T> },
+
+		// This pallet exposes the Error type explicitly.
+		Example: common::outer_enums::pallet::{Pallet, Config<T>, Event<T>, Error<T>},
+		Instance1Example: common::outer_enums::pallet::<Instance1>::{ Pallet, Config<T>, Event<T> },
+
+		// This pallet does not mention the Error type, but it must be propagated (similarly to the polkadot/kusama).
+		Example2: common::outer_enums::pallet2::{Pallet, Config<T>, Event<T> },
+		Instance1Example2: common::outer_enums::pallet2::<Instance1>::{Pallet, Config<T>, Event<T>},
+
+		// This pallet does not declare any errors.
+		Example3: common::outer_enums::pallet3::{Pallet, Config<T>, Event<T>},
+		Instance1Example3: common::outer_enums::pallet3::<Instance1>::{Pallet, Config<T>, Event<T>},
+	}
+);
+
+#[test]
+fn module_error_outer_enum_expand_explicit() {
+	// The Runtime has *all* parts explicitly defined.
+
+	// Check that all error types are propagated
+	match RuntimeError::Example(pallet::Error::InsufficientProposersBalance) {
+		// Error passed implicitely to the pallet system.
+		RuntimeError::System(system) => match system {
+			frame_system::Error::InvalidSpecName => (),
+			frame_system::Error::SpecVersionNeedsToIncrease => (),
+			frame_system::Error::FailedToExtractRuntimeVersion => (),
+			frame_system::Error::NonDefaultComposite => (),
+			frame_system::Error::NonZeroRefCount => (),
+			frame_system::Error::CallFiltered => (),
+			frame_system::Error::__Ignore(_, _) => (),
+		},
+
+		// Error declared explicitly.
+		RuntimeError::Example(example) => match example {
+			pallet::Error::InsufficientProposersBalance => (),
+			pallet::Error::NonExistentStorageValue => (),
+			pallet::Error::__Ignore(_, _) => (),
+		},
+		// Error declared explicitly.
+		RuntimeError::Instance1Example(example) => match example {
+			pallet::Error::InsufficientProposersBalance => (),
+			pallet::Error::NonExistentStorageValue => (),
+			pallet::Error::__Ignore(_, _) => (),
+		},
+
+		// Error must propagate even if not defined explicitly as pallet part.
+		RuntimeError::Example2(example) => match example {
+			pallet2::Error::OtherInsufficientProposersBalance => (),
+			pallet2::Error::OtherNonExistentStorageValue => (),
+			pallet2::Error::__Ignore(_, _) => (),
+		},
+		// Error must propagate even if not defined explicitly as pallet part.
+		RuntimeError::Instance1Example2(example) => match example {
+			pallet2::Error::OtherInsufficientProposersBalance => (),
+			pallet2::Error::OtherNonExistentStorageValue => (),
+			pallet2::Error::__Ignore(_, _) => (),
+		},
+	};
+}

substrate/frame/support/test/tests/pallet_outer_enums_implicit.rs

@@ -0,0 +1,140 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use frame_support::traits::ConstU32;
+
+mod common;
+
+use common::outer_enums::{pallet, pallet2};
+
+pub type Header = sp_runtime::generic::Header<u32, sp_runtime::traits::BlakeTwo256>;
+pub type Block = sp_runtime::generic::Block<Header, UncheckedExtrinsic>;
+pub type UncheckedExtrinsic = sp_runtime::generic::UncheckedExtrinsic<u32, RuntimeCall, (), ()>;
+
+impl frame_system::Config for Runtime {
+	type BaseCallFilter = frame_support::traits::Everything;
+	type RuntimeOrigin = RuntimeOrigin;
+	type Index = u64;
+	type BlockNumber = u32;
+	type RuntimeCall = RuntimeCall;
+	type Hash = sp_runtime::testing::H256;
+	type Hashing = sp_runtime::traits::BlakeTwo256;
+	type AccountId = u64;
+	type Lookup = sp_runtime::traits::IdentityLookup<Self::AccountId>;
+	type Header = Header;
+	type RuntimeEvent = RuntimeEvent;
+	type BlockHashCount = ConstU32<250>;
+	type BlockWeights = ();
+	type BlockLength = ();
+	type DbWeight = ();
+	type Version = ();
+	type PalletInfo = PalletInfo;
+	type AccountData = ();
+	type OnNewAccount = ();
+	type OnKilledAccount = ();
+	type SystemWeightInfo = ();
+	type SS58Prefix = ();
+	type OnSetCode = ();
+	type MaxConsumers = ConstU32<16>;
+}
+
+impl common::outer_enums::pallet::Config for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet::Config<common::outer_enums::pallet::Instance1> for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet2::Config for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet2::Config<common::outer_enums::pallet::Instance1> for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet3::Config for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+impl common::outer_enums::pallet3::Config<common::outer_enums::pallet::Instance1> for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+}
+
+frame_support::construct_runtime!(
+	pub struct Runtime where
+		Block = Block,
+		NodeBlock = Block,
+		UncheckedExtrinsic = UncheckedExtrinsic
+	{
+		// Exclude part `Storage` in order not to check its metadata in tests.
+		System: frame_system exclude_parts { Storage },
+
+		// Pallet exposes `Error` implicitely.
+		Example: common::outer_enums::pallet,
+		Instance1Example: common::outer_enums::pallet::<Instance1>,
+
+		// Pallet exposes `Error` implicitely.
+		Example2: common::outer_enums::pallet2,
+		Instance1Example2: common::outer_enums::pallet2::<Instance1>,
+
+		// Pallet does not implement error.
+		Example3: common::outer_enums::pallet3,
+		Instance1Example3: common::outer_enums::pallet3::<Instance1>,
+	}
+);
+
+#[test]
+fn module_error_outer_enum_expand_implicit() {
+	// The Runtime has *all* parts implicitly defined.
+
+	// Check that all error types are propagated
+	match RuntimeError::Example(pallet::Error::InsufficientProposersBalance) {
+		// Error passed implicitely to the pallet system.
+		RuntimeError::System(system) => match system {
+			frame_system::Error::InvalidSpecName => (),
+			frame_system::Error::SpecVersionNeedsToIncrease => (),
+			frame_system::Error::FailedToExtractRuntimeVersion => (),
+			frame_system::Error::NonDefaultComposite => (),
+			frame_system::Error::NonZeroRefCount => (),
+			frame_system::Error::CallFiltered => (),
+			frame_system::Error::__Ignore(_, _) => (),
+		},
+
+		// Error declared explicitly.
+		RuntimeError::Example(example) => match example {
+			pallet::Error::InsufficientProposersBalance => (),
+			pallet::Error::NonExistentStorageValue => (),
+			pallet::Error::__Ignore(_, _) => (),
+		},
+		// Error declared explicitly.
+		RuntimeError::Instance1Example(example) => match example {
+			pallet::Error::InsufficientProposersBalance => (),
+			pallet::Error::NonExistentStorageValue => (),
+			pallet::Error::__Ignore(_, _) => (),
+		},
+
+		// Error must propagate even if not defined explicitly as pallet part.
+		RuntimeError::Example2(example) => match example {
+			pallet2::Error::OtherInsufficientProposersBalance => (),
+			pallet2::Error::OtherNonExistentStorageValue => (),
+			pallet2::Error::__Ignore(_, _) => (),
+		},
+		// Error must propagate even if not defined explicitly as pallet part.
+		RuntimeError::Instance1Example2(example) => match example {
+			pallet2::Error::OtherInsufficientProposersBalance => (),
+			pallet2::Error::OtherNonExistentStorageValue => (),
+			pallet2::Error::__Ignore(_, _) => (),
+		},
+	};
+}

substrate/primitives/metadata-ir/Cargo.toml

@@ -14,7 +14,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 
 [dependencies]
 codec = { package = "parity-scale-codec", version = "3.6.1", default-features = false }
-frame-metadata = { version = "15.1.0", default-features = false, features = ["v14", "v15-unstable"] }
+frame-metadata = { version = "15.2.0", default-features = false, features = ["unstable"] }
 scale-info = { version = "2.1.1", default-features = false, features = ["derive"] }
 sp-std = { version = "8.0.0", default-features = false, path = "../std" }
 

substrate/primitives/metadata-ir/src/lib.rs

@@ -85,6 +85,11 @@ mod test {
 			},
 			ty: meta_type::<()>(),
 			apis: vec![],
+			outer_enums: OuterEnumsIR {
+				call_enum_ty: meta_type::<()>(),
+				event_enum_ty: meta_type::<()>(),
+				error_enum_ty: meta_type::<()>(),
+			},
 		}
 	}
 

substrate/primitives/metadata-ir/src/types.rs

@@ -39,6 +39,8 @@ pub struct MetadataIR<T: Form = MetaForm> {
 	pub ty: T::Type,
 	/// Metadata of the Runtime API.
 	pub apis: Vec<RuntimeApiMetadataIR<T>>,
+	/// The outer enums types as found in the runtime.
+	pub outer_enums: OuterEnumsIR<T>,
 }
 
 /// Metadata of a runtime trait.
@@ -398,3 +400,40 @@ impl From<MetaType> for PalletErrorMetadataIR {
 		Self { ty }
 	}
 }
+
+/// The type of the outer enums.
+#[derive(Clone, PartialEq, Eq, Encode, Debug)]
+pub struct OuterEnumsIR<T: Form = MetaForm> {
+	/// The type of the outer `RuntimeCall` enum.
+	pub call_enum_ty: T::Type,
+	/// The type of the outer `RuntimeEvent` enum.
+	pub event_enum_ty: T::Type,
+	/// The module error type of the
+	/// [`DispatchError::Module`](https://docs.rs/sp-runtime/24.0.0/sp_runtime/enum.DispatchError.html#variant.Module) variant.
+	///
+	/// The `Module` variant will be 5 scale encoded bytes which are normally decoded into
+	/// an `{ index: u8, error: [u8; 4] }` struct. This type ID points to an enum type which
+	/// instead interprets the first `index` byte as a pallet variant, and the remaining `error`
+	/// bytes as the appropriate `pallet::Error` type. It is an equally valid way to decode the
+	/// error bytes, and can be more informative.
+	///
+	/// # Note
+	///
+	/// - This type cannot be used directly to decode `sp_runtime::DispatchError` from the chain.
+	///   It provides just the information needed to decode `sp_runtime::DispatchError::Module`.
+	/// - Decoding the 5 error bytes into this type will not always lead to all of the bytes being
+	///   consumed; many error types do not require all of the bytes to represent them fully.
+	pub error_enum_ty: T::Type,
+}
+
+impl IntoPortable for OuterEnumsIR {
+	type Output = OuterEnumsIR<PortableForm>;
+
+	fn into_portable(self, registry: &mut Registry) -> Self::Output {
+		OuterEnumsIR {
+			call_enum_ty: registry.register_type(&self.call_enum_ty),
+			event_enum_ty: registry.register_type(&self.event_enum_ty),
+			error_enum_ty: registry.register_type(&self.error_enum_ty),
+		}
+	}
+}

substrate/primitives/metadata-ir/src/v15.rs

@@ -17,20 +17,17 @@
 
 //! Convert the IR to V15 metadata.
 
+use crate::OuterEnumsIR;
+
 use super::types::{
-	ExtrinsicMetadataIR, MetadataIR, PalletCallMetadataIR, PalletConstantMetadataIR,
-	PalletErrorMetadataIR, PalletEventMetadataIR, PalletMetadataIR, PalletStorageMetadataIR,
-	RuntimeApiMetadataIR, RuntimeApiMethodMetadataIR, RuntimeApiMethodParamMetadataIR,
-	SignedExtensionMetadataIR, StorageEntryMetadataIR, StorageEntryModifierIR, StorageEntryTypeIR,
-	StorageHasherIR,
+	ExtrinsicMetadataIR, MetadataIR, PalletMetadataIR, RuntimeApiMetadataIR,
+	RuntimeApiMethodMetadataIR, RuntimeApiMethodParamMetadataIR, SignedExtensionMetadataIR,
 };
 
 use frame_metadata::v15::{
-	ExtrinsicMetadata, PalletCallMetadata, PalletConstantMetadata, PalletErrorMetadata,
-	PalletEventMetadata, PalletMetadata, PalletStorageMetadata, RuntimeApiMetadata,
+	CustomMetadata, ExtrinsicMetadata, OuterEnums, PalletMetadata, RuntimeApiMetadata,
 	RuntimeApiMethodMetadata, RuntimeApiMethodParamMetadata, RuntimeMetadataV15,
-	SignedExtensionMetadata, StorageEntryMetadata, StorageEntryModifier, StorageEntryType,
-	StorageHasher,
+	SignedExtensionMetadata,
 };
 
 impl From<MetadataIR> for RuntimeMetadataV15 {
@@ -40,6 +37,10 @@ impl From<MetadataIR> for RuntimeMetadataV15 {
 			ir.extrinsic.into(),
 			ir.ty,
 			ir.apis.into_iter().map(Into::into).collect(),
+			ir.outer_enums.into(),
+			// Substrate does not collect yet the custom metadata fields.
+			// This allows us to extend the V15 easily.
+			CustomMetadata { map: Default::default() },
 		)
 	}
 }
@@ -86,87 +87,6 @@ impl From<PalletMetadataIR> for PalletMetadata {
 	}
 }
 
-impl From<StorageEntryModifierIR> for StorageEntryModifier {
-	fn from(ir: StorageEntryModifierIR) -> Self {
-		match ir {
-			StorageEntryModifierIR::Optional => StorageEntryModifier::Optional,
-			StorageEntryModifierIR::Default => StorageEntryModifier::Default,
-		}
-	}
-}
-
-impl From<StorageHasherIR> for StorageHasher {
-	fn from(ir: StorageHasherIR) -> Self {
-		match ir {
-			StorageHasherIR::Blake2_128 => StorageHasher::Blake2_128,
-			StorageHasherIR::Blake2_256 => StorageHasher::Blake2_256,
-			StorageHasherIR::Blake2_128Concat => StorageHasher::Blake2_128Concat,
-			StorageHasherIR::Twox128 => StorageHasher::Twox128,
-			StorageHasherIR::Twox256 => StorageHasher::Twox256,
-			StorageHasherIR::Twox64Concat => StorageHasher::Twox64Concat,
-			StorageHasherIR::Identity => StorageHasher::Identity,
-		}
-	}
-}
-
-impl From<StorageEntryTypeIR> for StorageEntryType {
-	fn from(ir: StorageEntryTypeIR) -> Self {
-		match ir {
-			StorageEntryTypeIR::Plain(ty) => StorageEntryType::Plain(ty),
-			StorageEntryTypeIR::Map { hashers, key, value } => StorageEntryType::Map {
-				hashers: hashers.into_iter().map(Into::into).collect(),
-				key,
-				value,
-			},
-		}
-	}
-}
-
-impl From<StorageEntryMetadataIR> for StorageEntryMetadata {
-	fn from(ir: StorageEntryMetadataIR) -> Self {
-		StorageEntryMetadata {
-			name: ir.name,
-			modifier: ir.modifier.into(),
-			ty: ir.ty.into(),
-			default: ir.default,
-			docs: ir.docs,
-		}
-	}
-}
-
-impl From<PalletStorageMetadataIR> for PalletStorageMetadata {
-	fn from(ir: PalletStorageMetadataIR) -> Self {
-		PalletStorageMetadata {
-			prefix: ir.prefix,
-			entries: ir.entries.into_iter().map(Into::into).collect(),
-		}
-	}
-}
-
-impl From<PalletCallMetadataIR> for PalletCallMetadata {
-	fn from(ir: PalletCallMetadataIR) -> Self {
-		PalletCallMetadata { ty: ir.ty }
-	}
-}
-
-impl From<PalletEventMetadataIR> for PalletEventMetadata {
-	fn from(ir: PalletEventMetadataIR) -> Self {
-		PalletEventMetadata { ty: ir.ty }
-	}
-}
-
-impl From<PalletConstantMetadataIR> for PalletConstantMetadata {
-	fn from(ir: PalletConstantMetadataIR) -> Self {
-		PalletConstantMetadata { name: ir.name, ty: ir.ty, value: ir.value, docs: ir.docs }
-	}
-}
-
-impl From<PalletErrorMetadataIR> for PalletErrorMetadata {
-	fn from(ir: PalletErrorMetadataIR) -> Self {
-		PalletErrorMetadata { ty: ir.ty }
-	}
-}
-
 impl From<SignedExtensionMetadataIR> for SignedExtensionMetadata {
 	fn from(ir: SignedExtensionMetadataIR) -> Self {
 		SignedExtensionMetadata {
@@ -180,9 +100,23 @@ impl From<SignedExtensionMetadataIR> for SignedExtensionMetadata {
 impl From<ExtrinsicMetadataIR> for ExtrinsicMetadata {
 	fn from(ir: ExtrinsicMetadataIR) -> Self {
 		ExtrinsicMetadata {
-			ty: ir.ty,
 			version: ir.version,
 			signed_extensions: ir.signed_extensions.into_iter().map(Into::into).collect(),
+			// Note: These fields are populated by complementary PR: https://github.com/paritytech/substrate/pull/14123.
+			address_ty: ir.ty,
+			call_ty: ir.ty,
+			signature_ty: ir.ty,
+			extra_ty: ir.ty,
+		}
+	}
+}
+
+impl From<OuterEnumsIR> for OuterEnums {
+	fn from(ir: OuterEnumsIR) -> Self {
+		OuterEnums {
+			call_enum_ty: ir.call_enum_ty,
+			event_enum_ty: ir.event_enum_ty,
+			error_enum_ty: ir.error_enum_ty,
 		}
 	}
 }