[frame] #[pallet::composite_enum] improved variant count handling + removed pallet_balances's MaxHolds config

cumulus/parachains/runtimes/assets/asset-hub-rococo/src/lib.rs

@@ -213,10 +213,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	// We allow each account to have holds on it from:
-	//   - `NftFractionalization`: 1
-	type MaxHolds = ConstU32<1>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/assets/asset-hub-westend/src/lib.rs

@@ -198,10 +198,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	// We allow each account to have holds on it from:
-	//   - `NftFractionalization`: 1
-	type MaxHolds = ConstU32<1>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-rococo/src/lib.rs

@@ -312,8 +312,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-westend/src/lib.rs

@@ -278,8 +278,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/collectives/collectives-westend/src/lib.rs

@@ -211,8 +211,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<1>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/contracts/contracts-rococo/src/lib.rs

@@ -217,8 +217,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<1>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/coretime/coretime-rococo/src/lib.rs

@@ -220,8 +220,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/coretime/coretime-westend/src/lib.rs

@@ -219,8 +219,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/people/people-rococo/src/lib.rs

@@ -218,8 +218,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/people/people-westend/src/lib.rs

@@ -218,8 +218,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/testing/penpal/src/lib.rs

@@ -405,8 +405,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

cumulus/parachains/runtimes/testing/rococo-parachain/src/lib.rs

@@ -258,8 +258,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<0>;
-	type MaxFreezes = ConstU32<0>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 impl pallet_transaction_payment::Config for Runtime {

polkadot/runtime/rococo/src/lib.rs

@@ -314,10 +314,10 @@ impl pallet_balances::Config for Runtime {
 	type ReserveIdentifier = [u8; 8];
 	type WeightInfo = weights::pallet_balances::WeightInfo<Runtime>;
 	type FreezeIdentifier = ();
-	type MaxFreezes = ConstU32<1>;
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
-	type MaxHolds = ConstU32<2>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {
@@ -1163,8 +1163,8 @@ impl pallet_balances::Config<NisCounterpartInstance> for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = ();
-	type MaxHolds = ConstU32<2>;
-	type MaxFreezes = ConstU32<1>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

polkadot/runtime/westend/src/lib.rs

@@ -303,8 +303,8 @@ impl pallet_balances::Config for Runtime {
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = RuntimeFreezeReason;
-	type MaxFreezes = ConstU32<1>;
-	type MaxHolds = ConstU32<1>;
+	type MaxHolds = RuntimeHoldReason;
+	type MaxFreezes = RuntimeFreezeReason;
 }
 
 parameter_types! {

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

@@ -68,3 +68,21 @@ pub(crate) fn expand_variant(
 		}
 	}
 }
+
+pub(crate) fn expand_variant_count(
+	composite_name: &str,
+	path: &PalletPath,
+	instance: Option<&Ident>,
+) -> TokenStream {
+	let composite_name = quote::format_ident!("{}", composite_name);
+
+	if let Some(inst) = instance {
+		quote! {
+			#path::#composite_name::<#path::#inst>::VARIANT_COUNT
+		}
+	} else {
+		quote! {
+			#path::#composite_name::VARIANT_COUNT
+		}
+	}
+}

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

@@ -23,6 +23,7 @@ use quote::quote;
 pub fn expand_outer_freeze_reason(pallet_decls: &[Pallet], scrate: &TokenStream) -> TokenStream {
 	let mut conversion_fns = Vec::new();
 	let mut freeze_reason_variants = Vec::new();
+	let mut freeze_reason_variants_count = Vec::new();
 	for decl in pallet_decls {
 		if let Some(_) = decl.find_part("FreezeReason") {
 			let variant_name = &decl.name;
@@ -44,9 +45,18 @@ pub fn expand_outer_freeze_reason(pallet_decls: &[Pallet], scrate: &TokenStream)
 				instance,
 				variant_name,
 			));
+
+			freeze_reason_variants_count.push(composite_helper::expand_variant_count(
+				"FreezeReason",
+				path,
+				instance,
+			));
 		}
 	}
-	let freeze_reason_variants_count = freeze_reason_variants.len() as u32;
+
+	if freeze_reason_variants_count.is_empty() {
+		freeze_reason_variants_count.push(quote! { 0 })
+	}
 
 	quote! {
 		/// A reason for placing a freeze on funds.
@@ -61,7 +71,14 @@ pub fn expand_outer_freeze_reason(pallet_decls: &[Pallet], scrate: &TokenStream)
 		}
 
 		impl #scrate::traits::VariantCount for RuntimeFreezeReason {
-			const VARIANT_COUNT: u32 = #freeze_reason_variants_count;
+			const VARIANT_COUNT: u32 = #( #freeze_reason_variants_count )+*;
+		}
+
+		/// Implementation of `Get<u32>` which returns `RuntimeFreezeReason::VARIANT_COUNT`.
+		impl #scrate::traits::Get<u32> for RuntimeFreezeReason {
+			fn get() -> u32 {
+				<RuntimeFreezeReason as #scrate::traits::VariantCount>::VARIANT_COUNT
+			}
 		}
 
 		#( #conversion_fns )*

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

@@ -23,6 +23,7 @@ use quote::quote;
 pub fn expand_outer_hold_reason(pallet_decls: &[Pallet], scrate: &TokenStream) -> TokenStream {
 	let mut conversion_fns = Vec::new();
 	let mut hold_reason_variants = Vec::new();
+	let mut hold_reason_variants_count = Vec::new();
 	for decl in pallet_decls {
 		if let Some(_) = decl.find_part("HoldReason") {
 			let variant_name = &decl.name;
@@ -44,9 +45,18 @@ pub fn expand_outer_hold_reason(pallet_decls: &[Pallet], scrate: &TokenStream) -
 				instance,
 				variant_name,
 			));
+
+			hold_reason_variants_count.push(composite_helper::expand_variant_count(
+				"HoldReason",
+				path,
+				instance,
+			));
 		}
 	}
-	let hold_reason_variants_count = hold_reason_variants.len() as u32;
+
+	if hold_reason_variants_count.is_empty() {
+		hold_reason_variants_count.push(quote! { 0 })
+	}
 
 	quote! {
 		/// A reason for placing a hold on funds.
@@ -61,7 +71,14 @@ pub fn expand_outer_hold_reason(pallet_decls: &[Pallet], scrate: &TokenStream) -
 		}
 
 		impl #scrate::traits::VariantCount for RuntimeHoldReason {
-			const VARIANT_COUNT: u32 = #hold_reason_variants_count;
+			const VARIANT_COUNT: u32 = #( #hold_reason_variants_count )+*;
+		}
+
+		/// Implementation of `Get<u32>` which returns `RuntimeHoldReason::VARIANT_COUNT`.
+		impl #scrate::traits::Get<u32> for RuntimeHoldReason {
+			fn get() -> u32 {
+				<RuntimeHoldReason as #scrate::traits::VariantCount>::VARIANT_COUNT
+			}
 		}
 
 		#( #conversion_fns )*

substrate/frame/support/procedural/src/lib.rs

@@ -1506,18 +1506,81 @@ pub fn origin(_: TokenStream, _: TokenStream) -> TokenStream {
 ///
 /// ```ignore
 /// Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Encode, Decode, MaxEncodedLen, TypeInfo,
-/// RuntimeDebug
+/// RuntimeDebug,
+/// CompositeEnumVariantCount,
 /// ```
 ///
 /// For ease of usage, when no `#[derive]` attributes are found for the enum under
 /// `#[pallet::composite_enum]`, the aforementioned traits are automatically derived for it. The
 /// inverse is also true: if there are any `#[derive]` attributes found for the enum, then no traits
-/// will automatically be derived for it.
+/// will automatically be derived for it (this implies that you need to provide the
+/// `frame_support::traits::VariantCount` implementation).
 #[proc_macro_attribute]
 pub fn composite_enum(_: TokenStream, _: TokenStream) -> TokenStream {
 	pallet_macro_stub()
 }
 
+/// Derive macro for implementing `frame_support::traits::VariantCount` for enum type.
+///
+/// This macro works only for the enum which does not have variants or variants do not have fields.
+///
+/// This macro is automatically derived for `#[pallet::composite_enum]` enums.
+#[proc_macro_derive(CompositeEnumVariantCount)]
+pub fn derive_composite_enum_variant_count(input: TokenStream) -> TokenStream {
+	let input: syn::DeriveInput = match syn::parse(input) {
+		Ok(input) => input,
+		Err(e) => return e.to_compile_error().into(),
+	};
+
+	// only `Enum` type is expected here (see also `CompositeDef::try_from`)
+	let data_enum = match &input.data {
+		syn::Data::Enum(ref data_enum) => data_enum,
+		_ =>
+			return syn::Error::new(input.ident.span(), "Invalid type: expected enum item")
+				.to_compile_error()
+				.into(),
+	};
+
+	// check variants: composite enums support only field-less enum variants. This is because fields
+	// can introduce too many possibilities, making it challenging to compute a fixed variant count.
+	// The only exception is `__Ignore` which can be added by `CompositeDef::try_from`.
+	for variant in &data_enum.variants {
+		match variant.fields {
+			syn::Fields::Named(_) | syn::Fields::Unnamed(_) => {
+				let variant_name = variant.ident.to_string();
+				if variant_name != "__Ignore" {
+					return syn::Error::new(
+						variant.ident.span(),
+						"The composite enum does not support variants with fields!",
+					)
+					.to_compile_error()
+					.into()
+				}
+			},
+			syn::Fields::Unit => (),
+		}
+	}
+	// get variants count
+	let variants_count = data_enum.variants.len() as u32;
+
+	// add `VariantCount` implementation for composite enum
+	let frame_support = match generate_access_from_frame_or_crate("frame-support") {
+		Ok(c) => c,
+		Err(e) => return e.into_compile_error().into(),
+	};
+	let frame_support = &frame_support;
+
+	let name = &input.ident;
+	let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+
+	quote! {
+		impl #impl_generics #frame_support::traits::VariantCount for #name #ty_generics #where_clause {
+			const VARIANT_COUNT: u32 = #variants_count;
+		}
+	}
+	.into()
+}
+
 ///
 /// ---
 ///

substrate/frame/support/procedural/src/pallet/parse/composite.rs

@@ -138,6 +138,7 @@ impl CompositeDef {
 					#scrate::__private::codec::Encode, #scrate::__private::codec::Decode, #scrate::__private::codec::MaxEncodedLen,
 					#scrate::__private::scale_info::TypeInfo,
 					#scrate::__private::RuntimeDebug,
+					#scrate::CompositeEnumVariantCount,
 				)]
 			};
 			item.attrs.push(derive_attr);