pallet-utility: if_else

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

@@ -99,4 +99,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 1_745
 			.saturating_add(Weight::from_parts(6_562_902, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

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

@@ -98,4 +98,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 3_765
 			.saturating_add(Weight::from_parts(6_028_416, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

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

@@ -98,4 +98,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 1_601
 			.saturating_add(Weight::from_parts(5_138_293, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

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

@@ -99,4 +99,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 1_601
 			.saturating_add(Weight::from_parts(5_138_293, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

cumulus/parachains/runtimes/collectives/collectives-westend/src/weights/pallet_utility.rs

@@ -98,4 +98,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 1_395
 			.saturating_add(Weight::from_parts(5_000_971, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

cumulus/parachains/runtimes/coretime/coretime-rococo/src/weights/pallet_utility.rs

@@ -99,4 +99,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 1_621
 			.saturating_add(Weight::from_parts(3_312_302, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

cumulus/parachains/runtimes/coretime/coretime-westend/src/weights/pallet_utility.rs

@@ -99,4 +99,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 740
 			.saturating_add(Weight::from_parts(2_800_888, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

cumulus/parachains/runtimes/people/people-rococo/src/weights/pallet_utility.rs

@@ -96,4 +96,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 3_915
 			.saturating_add(Weight::from_parts(4_372_646, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

cumulus/parachains/runtimes/people/people-westend/src/weights/pallet_utility.rs

@@ -96,4 +96,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 7_605
 			.saturating_add(Weight::from_parts(4_306_193, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

polkadot/runtime/rococo/src/weights/pallet_utility.rs

@@ -99,4 +99,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 460
 			.saturating_add(Weight::from_parts(3_173_577, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

polkadot/runtime/westend/src/weights/pallet_utility.rs

@@ -99,4 +99,12 @@ impl<T: frame_system::Config> pallet_utility::WeightInfo for WeightInfo<T> {
 			// Standard Error: 2_817
 			.saturating_add(Weight::from_parts(5_113_539, 0).saturating_mul(c.into()))
 	}
+	fn if_else() -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `0`
+		//  Estimated: `0`
+		// Minimum execution time: 6_000_000 picoseconds.
+		Weight::from_parts(7_000_000, 0)
+			.saturating_add(Weight::from_parts(0, 0))
+	}
 }

prdoc/pr_6321.prdoc

@@ -0,0 +1,33 @@
+title: Utility call fallback
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      This PR adds the `if_else` call to `pallet-utility`
+      enabling an error fallback when the main call is unsuccessful.
+
+crates:
+  - name: asset-hub-rococo-runtime
+    bump: major
+  - name: asset-hub-westend-runtime
+    bump: major
+  - name: bridge-hub-rococo-runtime
+    bump: major
+  - name: bridge-hub-westend-runtime
+    bump: major
+  - name: collectives-westend-runtime
+    bump: major
+  - name: coretime-rococo-runtime
+    bump: major
+  - name: coretime-westend-runtime
+    bump: major
+  - name: people-rococo-runtime
+    bump: major
+  - name: people-westend-runtime
+    bump: major
+  - name: rococo-runtime
+    bump: major
+  - name: westend-runtime
+    bump: major
+  - name: pallet-utility
+    bump: major

substrate/frame/utility/src/benchmarking.rs

@@ -92,6 +92,17 @@ mod benchmark {
 		assert_last_event::<T>(Event::BatchCompleted.into());
 	}
 
+	#[benchmark]
+	fn if_else() {
+		// Failing main call.
+		let main_call = Box::new(frame_system::Call::set_code { code: vec![1] }.into());
+		let fallback_call = Box::new(frame_system::Call::remark { remark: vec![1] }.into());
+		let caller = whitelisted_caller();
+
+		#[extrinsic_call]
+		_(RawOrigin::Signed(caller), main_call, fallback_call);
+	}
+
 	impl_benchmark_test_suite! {
 		Pallet,
 		tests::new_test_ext(),

substrate/frame/utility/src/lib.rs

@@ -61,7 +61,11 @@ extern crate alloc;
 use alloc::{boxed::Box, vec::Vec};
 use codec::{Decode, Encode};
 use frame_support::{
-	dispatch::{extract_actual_weight, GetDispatchInfo, PostDispatchInfo},
+	dispatch::{
+		extract_actual_weight,
+		DispatchClass::{Normal, Operational},
+		GetDispatchInfo, PostDispatchInfo,
+	},
 	traits::{IsSubType, OriginTrait, UnfilteredDispatchable},
 };
 use sp_core::TypeId;
@@ -120,6 +124,10 @@ pub mod pallet {
 		ItemFailed { error: DispatchError },
 		/// A call was dispatched.
 		DispatchedAs { result: DispatchResult },
+		/// Main call was dispatched.
+		IfElseMainSuccess,
+		/// The fallback call was dispatched.
+		IfElseFallbackCalled { main_error: DispatchError },
 	}
 
 	// Align the call size to 1KB. As we are currently compiling the runtime for native/wasm
@@ -454,6 +462,98 @@ pub mod pallet {
 			let res = call.dispatch_bypass_filter(frame_system::RawOrigin::Root.into());
 			res.map(|_| ()).map_err(|e| e.error)
 		}
+
+		/// Dispatch a fallback call in the event the main call fails to execute.
+		/// May be called from any origin except `None`.
+		///
+		/// This function first attempts to dispatch the `main` call.
+		/// If the `main` call fails, the `fallback` is attemted.
+		/// if the fallback is successfully dispatched, the weights of both calls
+		/// are accumulated and an event containing the main call error is deposited.
+		///
+		/// In the event of a fallback failure the whole call fails
+		/// with the weights returned.
+		///
+		/// - `main`: The main call to be dispatched. This is the primary action to execute.
+		/// - `fallback`: The fallback call to be dispatched in case the `main` call fails.
+		///
+		/// ## Dispatch Logic
+		/// - If the origin is `root`, both the main and fallback calls are executed without
+		///   applying any origin filters.
+		/// - If the origin is not `root`, the origin filter is applied to both the `main` and
+		///   `fallback` calls.
+		///
+		/// ## Use Case
+		/// - Some use cases might involve submitting a `batch` type call in either main, fallback
+		///   or both.
+		#[pallet::call_index(6)]
+		#[pallet::weight({
+			let main = main.get_dispatch_info();
+			let fallback = fallback.get_dispatch_info();
+			(
+				T::WeightInfo::if_else()
+					.saturating_add(main.call_weight)
+					.saturating_add(fallback.call_weight),
+				if main.class == Operational && fallback.class == Operational { Operational } else { Normal },
+			)
+		})]
+		pub fn if_else(
+			origin: OriginFor<T>,
+			main: Box<<T as Config>::RuntimeCall>,
+			fallback: Box<<T as Config>::RuntimeCall>,
+		) -> DispatchResultWithPostInfo {
+			// Do not allow the `None` origin.
+			if ensure_none(origin.clone()).is_ok() {
+				return Err(BadOrigin.into());
+			}
+
+			let is_root = ensure_root(origin.clone()).is_ok();
+
+			// Track the weights
+			let mut weight = T::WeightInfo::if_else();
+
+			let main_info = main.get_dispatch_info();
+
+			// Execute the main call first
+			let main_result = if is_root {
+				main.dispatch_bypass_filter(origin.clone())
+			} else {
+				main.dispatch(origin.clone())
+			};
+
+			// Add weight of the main call
+			weight = weight.saturating_add(extract_actual_weight(&main_result, &main_info));
+
+			let Err(main_error) = main_result else {
+				// If the main result is Ok, we skip the fallback logic entirely
+				Self::deposit_event(Event::IfElseMainSuccess);
+				return Ok(Some(weight).into());
+			};
+
+			// If the main call failed, execute the fallback call
+			let fallback_info = fallback.get_dispatch_info();
+
+			let fallback_result = if is_root {
+				fallback.dispatch_bypass_filter(origin.clone())
+			} else {
+				fallback.dispatch(origin)
+			};
+
+			// Add weight of the fallback call
+			weight = weight.saturating_add(extract_actual_weight(&fallback_result, &fallback_info));
+
+			let Err(fallback_error) = fallback_result else {
+				// Fallback succeeded.
+				Self::deposit_event(Event::IfElseFallbackCalled { main_error: main_error.error });
+				return Ok(Some(weight).into());
+			};
+
+			// Both calls have failed, return fallback error
+			Err(sp_runtime::DispatchErrorWithPostInfo {
+				error: fallback_error.error,
+				post_info: Some(weight).into(),
+			})
+		}
 	}
 
 	impl<T: Config> Pallet<T> {