Adds ability to provide defaults for types provided by construct_runtime

frame/balances/src/lib.rs

@@ -220,11 +220,14 @@ pub mod pallet {
 
 		pub struct TestDefaultConfig;
 
-		#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
+		#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig, no_aggregated_types)]
 		impl frame_system::DefaultConfig for TestDefaultConfig {}
 
 		#[frame_support::register_default_impl(TestDefaultConfig)]
 		impl DefaultConfig for TestDefaultConfig {
+			#[inject_runtime_type]
+			type RuntimeEvent = ();
+
 			type Balance = u64;
 
 			type ReserveIdentifier = ();
@@ -242,6 +245,7 @@ pub mod pallet {
 	#[pallet::config(with_default)]
 	pub trait Config<I: 'static = ()>: frame_system::Config {
 		/// The overarching event type.
+		#[pallet::no_default_bounds]
 		type RuntimeEvent: From<Event<Self, I>>
 			+ IsType<<Self as frame_system::Config>::RuntimeEvent>;
 

frame/examples/default-config/src/lib.rs

@@ -87,7 +87,7 @@ pub mod pallet {
 		/// A type providing default configurations for this pallet in testing environment.
 		pub struct TestDefaultConfig;
 
-		#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
+		#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig, no_aggregated_types)]
 		impl frame_system::DefaultConfig for TestDefaultConfig {}
 
 		#[frame_support::register_default_impl(TestDefaultConfig)]
@@ -109,7 +109,7 @@ pub mod pallet {
 		/// example, we simple derive `frame_system::config_preludes::TestDefaultConfig` again.
 		pub struct OtherDefaultConfig;
 
-		#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
+		#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig, no_aggregated_types)]
 		impl frame_system::DefaultConfig for OtherDefaultConfig {}
 
 		#[frame_support::register_default_impl(OtherDefaultConfig)]
@@ -147,16 +147,7 @@ pub mod tests {
 	#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
 	impl frame_system::Config for Runtime {
 		// these items are defined by frame-system as `no_default`, so we must specify them here.
-		// Note that these are types that actually rely on the outer runtime, and can't sensibly
-		// have an _independent_ default.
 		type Block = Block;
-		type BlockHashCount = frame_support::traits::ConstU64<10>;
-		type BaseCallFilter = frame_support::traits::Everything;
-		type RuntimeOrigin = RuntimeOrigin;
-		type RuntimeCall = RuntimeCall;
-		type RuntimeEvent = RuntimeEvent;
-		type PalletInfo = PalletInfo;
-		type OnSetCode = ();
 
 		// all of this is coming from `frame_system::config_preludes::TestDefaultConfig`.
 
@@ -177,6 +168,17 @@ pub mod tests {
 		// type BlockWeights = ();
 		// type BlockLength = ();
 		// type DbWeight = ();
+		// type BaseCallFilter = frame_support::traits::Everything;
+		// type BlockHashCount = frame_support::traits::ConstU64<10>;
+		// type OnSetCode = ();
+
+		// These are marked as `#[inject_runtime_type]`. Hence, they are being injected as
+		// types generated by `construct_runtime`.
+
+		// type RuntimeOrigin = RuntimeOrigin;
+		// type RuntimeCall = RuntimeCall;
+		// type RuntimeEvent = RuntimeEvent;
+		// type PalletInfo = PalletInfo;
 
 		// you could still overwrite any of them if desired.
 		type SS58Prefix = frame_support::traits::ConstU16<456>;

frame/support/Cargo.toml

@@ -44,6 +44,7 @@ environmental = { version = "1.1.4", default-features = false }
 sp-genesis-builder = { version = "0.1.0", default-features=false, path = "../../primitives/genesis-builder" }
 serde_json = { version = "1.0.85", default-features = false, features = ["alloc"] }
 docify = "0.2.1"
+static_assertions = "1.1.0"
 
 aquamarine = { version = "0.3.2" }
 

frame/support/procedural/src/derive_impl.rs

@@ -22,14 +22,46 @@ use macro_magic::mm_core::ForeignPath;
 use proc_macro2::TokenStream as TokenStream2;
 use quote::{quote, ToTokens};
 use std::collections::HashSet;
-use syn::{parse2, parse_quote, spanned::Spanned, Ident, ImplItem, ItemImpl, Path, Result, Token};
+use syn::{
+	parse2, parse_quote, spanned::Spanned, token, Ident, ImplItem, ItemImpl, Path, Result, Token,
+};
 
-#[derive(Parse)]
+mod keyword {
+	syn::custom_keyword!(inject_runtime_type);
+	syn::custom_keyword!(no_aggregated_types);
+}
+
+#[derive(derive_syn_parse::Parse, PartialEq, Eq)]
+pub enum PalletAttrType {
+	#[peek(keyword::inject_runtime_type, name = "inject_runtime_type")]
+	RuntimeType(keyword::inject_runtime_type),
+}
+
+#[derive(derive_syn_parse::Parse)]
+pub struct PalletAttr {
+	_pound: Token![#],
+	#[bracket]
+	_bracket: token::Bracket,
+	#[inside(_bracket)]
+	typ: PalletAttrType,
+}
+
+fn get_first_item_pallet_attr<Attr>(item: &syn::ImplItemType) -> syn::Result<Option<Attr>>
+where
+	Attr: syn::parse::Parse,
+{
+	item.attrs.get(0).map(|a| syn::parse2(a.into_token_stream())).transpose()
+}
+
+#[derive(Parse, Debug)]
 pub struct DeriveImplAttrArgs {
 	pub default_impl_path: Path,
 	_as: Option<Token![as]>,
 	#[parse_if(_as.is_some())]
 	pub disambiguation_path: Option<Path>,
+	_comma: Option<Token![,]>,
+	#[parse_if(_comma.is_some())]
+	pub no_aggregated_types: Option<keyword::no_aggregated_types>,
 }
 
 impl ForeignPath for DeriveImplAttrArgs {
@@ -43,6 +75,8 @@ impl ToTokens for DeriveImplAttrArgs {
 		tokens.extend(self.default_impl_path.to_token_stream());
 		tokens.extend(self._as.to_token_stream());
 		tokens.extend(self.disambiguation_path.to_token_stream());
+		tokens.extend(self._comma.to_token_stream());
+		tokens.extend(self.no_aggregated_types.to_token_stream());
 	}
 }
 
@@ -78,6 +112,7 @@ fn combine_impls(
 	foreign_impl: ItemImpl,
 	default_impl_path: Path,
 	disambiguation_path: Path,
+	inject_runtime_types: bool,
 ) -> ItemImpl {
 	let (existing_local_keys, existing_unsupported_items): (HashSet<ImplItem>, HashSet<ImplItem>) =
 		local_impl
@@ -96,7 +131,20 @@ fn combine_impls(
 				// do not copy colliding items that have an ident
 				return None
 			}
-			if matches!(item, ImplItem::Type(_)) {
+			if let ImplItem::Type(typ) = item.clone() {
+				let mut typ = typ.clone();
+				if let Ok(Some(PalletAttr { typ: PalletAttrType::RuntimeType(_), .. })) =
+					get_first_item_pallet_attr::<PalletAttr>(&mut typ)
+				{
+					let item: ImplItem = if inject_runtime_types {
+						parse_quote! {
+							type #ident = #ident;
+						}
+					} else {
+						item
+					};
+					return Some(item)
+				}
 				// modify and insert uncolliding type items
 				let modified_item: ImplItem = parse_quote! {
 					type #ident = <#default_impl_path as #disambiguation_path>::#ident;
@@ -132,6 +180,7 @@ pub fn derive_impl(
 	foreign_tokens: TokenStream2,
 	local_tokens: TokenStream2,
 	disambiguation_path: Option<Path>,
+	no_aggregated_types: Option<keyword::no_aggregated_types>,
 ) -> Result<TokenStream2> {
 	let local_impl = parse2::<ItemImpl>(local_tokens)?;
 	let foreign_impl = parse2::<ItemImpl>(foreign_tokens)?;
@@ -151,8 +200,13 @@ pub fn derive_impl(
 	};
 
 	// generate the combined impl
-	let combined_impl =
-		combine_impls(local_impl, foreign_impl, default_impl_path, disambiguation_path);
+	let combined_impl = combine_impls(
+		local_impl,
+		foreign_impl,
+		default_impl_path,
+		disambiguation_path,
+		no_aggregated_types.is_none(),
+	);
 
 	Ok(quote!(#combined_impl))
 }

frame/support/procedural/src/lib.rs

@@ -38,7 +38,7 @@ use macro_magic::import_tokens_attr;
 use proc_macro::TokenStream;
 use quote::{quote, ToTokens};
 use std::{cell::RefCell, str::FromStr};
-use syn::{parse_macro_input, Error, ItemImpl, ItemMod};
+use syn::{parse_macro_input, Error, ItemImpl, ItemMod, TraitItemType};
 
 pub(crate) const INHERENT_INSTANCE_NAME: &str = "__InherentHiddenInstance";
 
@@ -596,6 +596,19 @@ pub fn storage_alias(attributes: TokenStream, input: TokenStream) -> TokenStream
 ///
 /// Conversely, the `default_impl_path` argument is required and cannot be omitted.
 ///
+/// Optionally, `no_aggregated_types` can be specified as follows:
+///
+/// ```ignore
+/// #[derive_impl(default_impl_path as disambiguation_path, no_aggregated_types)]
+/// impl SomeTrait for SomeStruct {
+///     ...
+/// }
+/// ```
+///
+/// If specified, this indicates that the aggregated types (as denoted by impl items
+/// attached with [`#[inject_runtime_type]`]) should not be injected with the respective concrete
+/// types. By default, all such types are injected.
+///
 /// You can also make use of `#[pallet::no_default]` on specific items in your default impl that you
 /// want to ensure will not be copied over but that you nonetheless want to use locally in the
 /// context of the foreign impl and the pallet (or context) in which it is defined.
@@ -759,6 +772,7 @@ pub fn derive_impl(attrs: TokenStream, input: TokenStream) -> TokenStream {
 		attrs.into(),
 		input.into(),
 		custom_attrs.disambiguation_path,
+		custom_attrs.no_aggregated_types,
 	)
 	.unwrap_or_else(|r| r.into_compile_error())
 	.into()
@@ -774,6 +788,19 @@ pub fn no_default(_: TokenStream, _: TokenStream) -> TokenStream {
 	pallet_macro_stub()
 }
 
+/// The optional attribute `#[pallet::no_default_bounds]` can be attached to trait items within a
+/// `Config` trait impl that has [`#[pallet::config(with_default)]`](`macro@config`) attached.
+///
+/// Attaching this attribute to a trait item ensures that the generated trait `DefaultConfig`
+/// will not have any bounds for this trait item.
+///
+/// As an example, if you have a trait item `type AccountId: SomeTrait;` in your `Config` trait,
+/// the generated `DefaultConfig` will only have `type AccountId;` with no trait bound.
+#[proc_macro_attribute]
+pub fn no_default_bounds(_: TokenStream, _: TokenStream) -> TokenStream {
+	pallet_macro_stub()
+}
+
 /// Attach this attribute to an impl statement that you want to use with
 /// [`#[derive_impl(..)]`](`macro@derive_impl`).
 ///
@@ -843,6 +870,25 @@ pub fn register_default_impl(attrs: TokenStream, tokens: TokenStream) -> TokenSt
 	}
 }
 
+#[proc_macro_attribute]
+pub fn inject_runtime_type(_: TokenStream, tokens: TokenStream) -> TokenStream {
+	let item = tokens.clone();
+	let item = syn::parse_macro_input!(item as TraitItemType);
+	if item.ident != "RuntimeCall" &&
+		item.ident != "RuntimeEvent" &&
+		item.ident != "RuntimeOrigin" &&
+		item.ident != "PalletInfo"
+	{
+		return syn::Error::new_spanned(
+			item,
+			"`#[inject_runtime_type]` can only be attached to `RuntimeCall`, `RuntimeEvent`, `RuntimeOrigin` or `PalletInfo`",
+		)
+		.to_compile_error()
+		.into();
+	}
+	tokens
+}
+
 /// Used internally to decorate pallet attribute macro stubs when they are erroneously used
 /// outside of a pallet module
 fn pallet_macro_stub() -> TokenStream {

frame/support/procedural/src/pallet/expand/config.rs

@@ -52,7 +52,23 @@ Consequently, a runtime that wants to include this pallet must implement this tr
 	// impossible consequently.
 	match &config.default_sub_trait {
 		Some(default_sub_trait) if default_sub_trait.items.len() > 0 => {
-			let trait_items = &default_sub_trait.items;
+			let trait_items = &default_sub_trait
+				.items
+				.iter()
+				.map(|item| {
+					if item.1 {
+						if let syn::TraitItem::Type(item) = item.0.clone() {
+							let mut item = item.clone();
+							item.bounds.clear();
+							syn::TraitItem::Type(item)
+						} else {
+							item.0.clone()
+						}
+					} else {
+						item.0.clone()
+					}
+				})
+				.collect::<Vec<_>>();
 
 			let type_param_bounds = if default_sub_trait.has_system {
 				let system = &def.frame_system;

frame/support/procedural/src/pallet/parse/config.rs

@@ -34,12 +34,16 @@ mod keyword {
 	syn::custom_keyword!(frame_system);
 	syn::custom_keyword!(disable_frame_system_supertrait_check);
 	syn::custom_keyword!(no_default);
+	syn::custom_keyword!(no_default_bounds);
 	syn::custom_keyword!(constant);
 }
 
 #[derive(Default)]
 pub struct DefaultTrait {
-	pub items: Vec<syn::TraitItem>,
+	/// A bool for each sub-trait item indicates whether the item has
+	/// `#[pallet::no_default_bounds]` attached to it. If true, the item will not have any bounds
+	/// in the generated default sub-trait.
+	pub items: Vec<(syn::TraitItem, bool)>,
 	pub has_system: bool,
 }
 
@@ -142,6 +146,8 @@ impl syn::parse::Parse for DisableFrameSystemSupertraitCheck {
 pub enum PalletAttrType {
 	#[peek(keyword::no_default, name = "no_default")]
 	NoDefault(keyword::no_default),
+	#[peek(keyword::no_default_bounds, name = "no_default_bounds")]
+	NoBounds(keyword::no_default_bounds),
 	#[peek(keyword::constant, name = "constant")]
 	Constant(keyword::constant),
 }
@@ -366,6 +372,7 @@ impl ConfigDef {
 
 			let mut already_no_default = false;
 			let mut already_constant = false;
+			let mut already_no_default_bounds = false;
 
 			while let Ok(Some(pallet_attr)) =
 				helper::take_first_item_pallet_attr::<PalletAttr>(trait_item)
@@ -403,15 +410,31 @@ impl ConfigDef {
 
 						already_no_default = true;
 					},
+					(PalletAttrType::NoBounds(_), _) => {
+						if !enable_default {
+							return Err(syn::Error::new(
+								pallet_attr._bracket.span.join(),
+								"`#[pallet:no_default_bounds]` can only be used if `#[pallet::config(with_default)]` \
+								has been specified"
+							))
+						}
+						if already_no_default_bounds {
+							return Err(syn::Error::new(
+								pallet_attr._bracket.span.join(),
+								"Duplicate #[pallet::no_default_bounds] attribute not allowed.",
+							))
+						}
+						already_no_default_bounds = true;
+					},
 				}
 			}
 
-			if !already_no_default && !is_event && enable_default {
+			if !already_no_default && enable_default {
 				default_sub_trait
 					.as_mut()
 					.expect("is 'Some(_)' if 'enable_default'; qed")
 					.items
-					.push(trait_item.clone());
+					.push((trait_item.clone(), already_no_default_bounds));
 			}
 		}