[xcm-builder][origin_conversion] LocationAsSuperuser converter introduced

polkadot/xcm/xcm-builder/src/origin_conversion.rs

@@ -17,7 +17,7 @@
 //! Various implementations for `ConvertOrigin`.
 
 use core::marker::PhantomData;
-use frame_support::traits::{EnsureOrigin, Get, GetBacking, OriginTrait};
+use frame_support::traits::{Contains, EnsureOrigin, Get, GetBacking, OriginTrait};
 use frame_system::RawOrigin as SystemRawOrigin;
 use polkadot_parachain_primitives::primitives::IsSystem;
 use sp_runtime::traits::TryConvert;
@@ -332,3 +332,123 @@ impl<RuntimeOrigin: Clone, EnsureBodyOrigin: EnsureOrigin<RuntimeOrigin>, Body:
 		}
 	}
 }
+
+/// Implements `ConvertOrigin` to convert a `Location` into `RuntimeOrigin::root()`.
+///
+/// This is typically used when configuring `pallet-xcm` to allow a remote `Location`
+/// to act as the `Root` origin on the local chain.
+pub struct LocationAsSuperuser<SuperuserLocation, RuntimeOrigin>(
+	PhantomData<(SuperuserLocation, RuntimeOrigin)>,
+);
+impl<SuperuserLocation: Contains<Location>, RuntimeOrigin: OriginTrait> ConvertOrigin<RuntimeOrigin>
+	for LocationAsSuperuser<SuperuserLocation, RuntimeOrigin>
+{
+	fn convert_origin(
+		origin: impl Into<Location>,
+		kind: OriginKind,
+	) -> Result<RuntimeOrigin, Location> {
+		let origin = origin.into();
+		tracing::trace!(
+			target: "xcm::origin_conversion",
+			?origin, ?kind,
+			"LocationAsSuperuser",
+		);
+		match (kind, &origin) {
+			(OriginKind::Superuser, loc) if SuperuserLocation::contains(loc) =>
+				Ok(RuntimeOrigin::root()),
+			_ => Err(origin),
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use frame_support::{construct_runtime, derive_impl, parameter_types, traits::Equals};
+	use xcm::latest::{Junction::*, OriginKind};
+
+	type Block = frame_system::mocking::MockBlock<Test>;
+
+	construct_runtime!(
+		pub enum Test
+		{
+			System: frame_system,
+		}
+	);
+
+	#[derive_impl(frame_system::config_preludes::TestDefaultConfig)]
+	impl frame_system::Config for Test {
+		type Block = Block;
+	}
+
+	parameter_types! {
+		pub SuperuserLocation: Location = Location::new(0, Parachain(1));
+	}
+
+	#[test]
+	fn superuser_location_works() {
+		let test_conversion = |loc, kind| {
+			LocationAsSuperuser::<Equals<SuperuserLocation>, RuntimeOrigin>::convert_origin(
+				loc, kind,
+			)
+		};
+
+		// Location that was set as SuperUserLocation should result in success conversion to Root
+		assert!(matches!(test_conversion(SuperuserLocation::get(), OriginKind::Superuser), Ok(..)));
+		// Same Location as SuperUserLocation::get()
+		assert!(matches!(
+			test_conversion(Location::new(0, Parachain(1)), OriginKind::Superuser),
+			Ok(..)
+		));
+
+		// Same Location but different origin kind
+		assert!(matches!(test_conversion(SuperuserLocation::get(), OriginKind::Native), Err(..)));
+		assert!(matches!(
+			test_conversion(SuperuserLocation::get(), OriginKind::SovereignAccount),
+			Err(..)
+		));
+		assert!(matches!(test_conversion(SuperuserLocation::get(), OriginKind::Xcm), Err(..)));
+
+		// No other location should result in successful conversion to Root
+		// thus expecting Err in all cases below
+		//
+		// Non-matching parachain number
+		assert!(matches!(
+			test_conversion(Location::new(0, Parachain(2)), OriginKind::Superuser),
+			Err(..)
+		));
+		// Non-matching parents count
+		assert!(matches!(
+			test_conversion(Location::new(1, Parachain(1)), OriginKind::Superuser),
+			Err(..)
+		));
+		// Child location of SuperUserLocation
+		assert!(matches!(
+			test_conversion(
+				Location::new(1, [Parachain(1), GeneralIndex(0)]),
+				OriginKind::Superuser
+			),
+			Err(..)
+		));
+		// Here
+		assert!(matches!(test_conversion(Location::new(0, Here), OriginKind::Superuser), Err(..)));
+		// Parent
+		assert!(matches!(test_conversion(Location::new(1, Here), OriginKind::Superuser), Err(..)));
+		// Some random account
+		assert!(matches!(
+			test_conversion(
+				Location::new(0, AccountId32 { network: None, id: [0u8; 32] }),
+				OriginKind::Superuser
+			),
+			Err(..)
+		));
+		// Child location of SuperUserLocation
+		assert!(matches!(
+			test_conversion(
+				Location::new(0, [Parachain(1), AccountId32 { network: None, id: [1u8; 32] }]),
+				OriginKind::Superuser
+			),
+			Err(..)
+		));
+	}
+}