Adds ability to provide defaults for types provided by construct_runtime

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

@@ -107,7 +107,6 @@ pub mod pallet {
 pub mod tests {
 	use super::*;
 	use frame_support::derive_impl;
-	use sp_runtime::traits::ConstU64;
 
 	use super::pallet as pallet_default_config_example;
 
@@ -123,18 +122,6 @@ pub mod tests {
 
 	#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
 	impl frame_system::Config for Test {
-		// 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 = 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`.
 
 		// type Nonce = u32;
@@ -157,6 +144,18 @@ pub mod tests {
 		// type BlockWeights = ();
 		// type BlockLength = ();
 		// type DbWeight = ();
+		// type BaseCallFilter = frame_support::traits::Everything;
+		// type BlockHashCount = ConstU64<10>;
+		// type OnSetCode = ();
+
+		// These are marked as `#[verbatim]`. Hence, they are being injected as
+		// defaults with same names.
+
+		// type Block = Block;
+		// 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/procedural/src/derive_impl.rs

@@ -22,7 +22,40 @@ 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,
+};
+
+mod keyword {
+	syn::custom_keyword!(verbatim);
+}
+
+#[derive(derive_syn_parse::Parse, PartialEq, Eq)]
+pub enum PalletAttrType {
+	#[peek(keyword::verbatim, name = "verbatim")]
+	Verbatim(keyword::verbatim),
+}
+
+#[derive(derive_syn_parse::Parse)]
+pub struct PalletAttr {
+	_pound: Token![#],
+	#[bracket]
+	_bracket: token::Bracket,
+	#[inside(_bracket)]
+	typ: PalletAttrType,
+}
+
+fn take_first_item_pallet_attr<Attr>(item: &mut syn::ImplItemType) -> syn::Result<Option<Attr>>
+where
+	Attr: syn::parse::Parse,
+{
+	let attrs = &mut item.attrs;
+	if let Some(pallet_attr) = attrs.get(0) {
+		Ok(Some(syn::parse2(pallet_attr.into_token_stream())?))
+	} else {
+		Ok(None)
+	}
+}
 
 #[derive(Parse)]
 pub struct DeriveImplAttrArgs {
@@ -96,7 +129,19 @@ fn combine_impls(
 				// do not copy colliding items that have an ident
 				return None
 			}
-			if matches!(item, ImplItem::Type(_)) {
+			if let ImplItem::Type(item) = item.clone() {
+				let mut item = item.clone();
+				if let Ok(Some(pallet_attr)) = take_first_item_pallet_attr::<PalletAttr>(&mut item)
+				{
+					match pallet_attr.typ {
+						PalletAttrType::Verbatim(_) => {
+							let modified_item: ImplItem = parse_quote! {
+								type #ident = #ident;
+							};
+							return Some(modified_item)
+						},
+					}
+				}
 				// modify and insert uncolliding type items
 				let modified_item: ImplItem = parse_quote! {
 					type #ident = <#default_impl_path as #disambiguation_path>::#ident;

frame/support/procedural/src/lib.rs

@@ -774,6 +774,19 @@ pub fn no_default(_: TokenStream, _: TokenStream) -> TokenStream {
 	pallet_macro_stub()
 }
 
+/// The optional attribute `#[pallet::no_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_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 +856,19 @@ pub fn register_default_impl(attrs: TokenStream, tokens: TokenStream) -> TokenSt
 	}
 }
 
+/// The optional attribute `#[verbatim]` can be attached to any item in an impl
+/// statement that has `#[register_default_impl]` attached.
+///
+/// Attaching this attribute to an item ensures that the combined impl generated via
+/// [`#[derive_impl(..)]`](`macro@derive_impl`)  will use the same name for the default.
+///
+/// As an example, if you have an impl item `#[verbatim] type RuntimeEvent = ();` in
+/// your impl statement, the combined impl will have `type RuntimeEvent = RuntimeEvent;` instead.
+#[proc_macro_attribute]
+pub fn verbatim(_: TokenStream, tokens: TokenStream) -> TokenStream {
+	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

@@ -51,7 +51,23 @@ Consequently, a runtime that wants to include this pallet must implement this tr
 	// we only emit `DefaultConfig` if there are trait items, so an empty `DefaultConfig` is
 	// impossible consequently
 	if config.default_sub_trait.len() > 0 {
-		let trait_items = &config.default_sub_trait;
+		let trait_items = &config
+			.default_sub_trait
+			.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<_>>();
 		quote!(
 			/// Based on [`Config`]. Auto-generated by
 			/// [`#[pallet::config(with_default)]`](`frame_support::pallet_macros::config`).

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

@@ -34,6 +34,7 @@ mod keyword {
 	syn::custom_keyword!(frame_system);
 	syn::custom_keyword!(disable_frame_system_supertrait_check);
 	syn::custom_keyword!(no_default);
+	syn::custom_keyword!(no_bounds);
 	syn::custom_keyword!(constant);
 }
 
@@ -59,7 +60,11 @@ pub struct ConfigDef {
 	/// Contains default sub-trait items (instantiated by `#[pallet::config(with_default)]`).
 	/// Vec will be empty if `#[pallet::config(with_default)]` is not specified or if there are
 	/// no trait items
-	pub default_sub_trait: Vec<syn::TraitItem>,
+	///
+	/// A bool for each sub-trait item indicates whether the item has `#[pallet::no_bounds]`
+	/// attached to it. If true, the item will not have any bounds in the generated default
+	/// sub-trait.
+	pub default_sub_trait: Vec<(syn::TraitItem, bool)>,
 }
 
 /// Input definition for a constant in pallet config.
@@ -136,6 +141,8 @@ impl syn::parse::Parse for DisableFrameSystemSupertraitCheck {
 pub enum PalletAttrType {
 	#[peek(keyword::no_default, name = "no_default")]
 	NoDefault(keyword::no_default),
+	#[peek(keyword::no_bounds, name = "no_bounds")]
+	NoBounds(keyword::no_bounds),
 	#[peek(keyword::constant, name = "constant")]
 	Constant(keyword::constant),
 }
@@ -348,6 +355,7 @@ impl ConfigDef {
 
 			let mut already_no_default = false;
 			let mut already_constant = false;
+			let mut already_no_bounds = false;
 
 			while let Ok(Some(pallet_attr)) =
 				helper::take_first_item_pallet_attr::<PalletAttr>(trait_item)
@@ -384,11 +392,27 @@ impl ConfigDef {
 						}
 						already_no_default = true;
 					},
+					(PalletAttrType::NoBounds(_), _) => {
+						if !enable_default {
+							return Err(syn::Error::new(
+								pallet_attr._bracket.span.join(),
+								"`#[pallet:no_bounds]` can only be used if `#[pallet::config(with_default)]` \
+								has been specified"
+							))
+						}
+						if already_no_bounds {
+							return Err(syn::Error::new(
+								pallet_attr._bracket.span.join(),
+								"Duplicate #[pallet::no_bounds] attribute not allowed.",
+							))
+						}
+						already_no_bounds = true;
+					},
 				}
 			}
 
-			if !already_no_default && !is_event && enable_default {
-				default_sub_trait.push(trait_item.clone());
+			if !already_no_default && enable_default {
+				default_sub_trait.push((trait_item.clone(), already_no_bounds));
 			}
 		}
 

frame/support/src/lib.rs

@@ -2905,8 +2905,8 @@ pub mod pallet_macros {
 		call_index, compact, composite_enum, config, constant,
 		disable_frame_system_supertrait_check, error, event, extra_constants, generate_deposit,
 		generate_store, genesis_build, genesis_config, getter, hooks, import_section, inherent,
-		no_default, origin, pallet_section, storage, storage_prefix, storage_version, type_value,
-		unbounded, validate_unsigned, weight, whitelist_storage,
+		no_bounds, no_default, origin, pallet_section, storage, storage_prefix, storage_version,
+		type_value, unbounded, validate_unsigned, verbatim, weight, whitelist_storage,
 	};
 }
 

frame/support/test/tests/derive_impl_ui/pass/verbatim_working.rs

@@ -0,0 +1,25 @@
+use frame_support::{*, pallet_macros::verbatim};
+use static_assertions::assert_type_eq_all;
+
+pub trait Shape {
+    type Area;
+}
+
+type Area = f32;
+
+struct DefaultShape;
+
+#[register_default_impl(DefaultShape)]
+impl Shape for DefaultShape {
+    #[verbatim]
+    type Area = ();
+}
+
+struct Circle;
+
+#[derive_impl(DefaultShape)] // Injects type Area = Area;
+impl Shape for Circle {}
+
+assert_type_eq_all!(<Circle as Shape>::Area, Area);
+
+fn main() {}

frame/support/test/tests/derive_impl_ui/verbatim_fails_when_type_not_in_scope.rs

@@ -0,0 +1,23 @@
+use frame_support::{*, pallet_macros::verbatim};
+use static_assertions::assert_type_eq_all;
+
+pub trait Shape {
+    type Area;
+}
+
+struct DefaultShape;
+
+#[register_default_impl(DefaultShape)]
+impl Shape for DefaultShape {
+    #[verbatim]
+    type Area = ();
+}
+
+struct Circle;
+
+#[derive_impl(DefaultShape)] // Injects type Area = Area;
+impl Shape for Circle {}
+
+assert_type_eq_all!(<Circle as Shape>::Area, Area);
+
+fn main() {}

frame/support/test/tests/derive_impl_ui/verbatim_fails_when_type_not_in_scope.stderr

@@ -0,0 +1,16 @@
+error[E0412]: cannot find type `Area` in this scope
+  --> tests/derive_impl_ui/verbatim_fails_when_type_not_in_scope.rs:13:10
+   |
+13 |     type Area = ();
+   |          ^^^^ help: you might have meant to use the associated type: `Self::Area`
+...
+18 | #[derive_impl(DefaultShape)] // Injects type Area = Area;
+   | ---------------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `__export_tokens_tt_default_shape` which comes from the expansion of the macro `frame_support::macro_magic::forward_tokens` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0412]: cannot find type `Area` in this scope
+  --> tests/derive_impl_ui/verbatim_fails_when_type_not_in_scope.rs:21:46
+   |
+21 | assert_type_eq_all!(<Circle as Shape>::Area, Area);
+   |                                              ^^^^ not found in this scope

frame/support/test/tests/pallet_ui/no_bounds_but_missing_with_default.rs

@@ -0,0 +1,23 @@
+#[frame_support::pallet]
+mod pallet {
+	use frame_support::pallet_prelude::*;
+	use frame_system::pallet_prelude::*;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {
+		#[pallet::constant]
+		#[pallet::no_bounds]
+		type MyGetParam2: Get<u32>;
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+	#[pallet::hooks]
+	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}
+
+	#[pallet::call]
+	impl<T: Config> Pallet<T> {}
+}
+
+fn main() {}

frame/support/test/tests/pallet_ui/no_bounds_but_missing_with_default.stderr

@@ -0,0 +1,5 @@
+error: `#[pallet:no_bounds]` can only be used if `#[pallet::config(with_default)]` has been specified
+ --> tests/pallet_ui/no_bounds_but_missing_with_default.rs:9:4
+  |
+9 |         #[pallet::no_bounds]
+  |          ^^^^^^^^^^^^^^^^^^^