Dedup nomination targets

substrate/frame/staking/src/pallet/mod.rs

@@ -1470,21 +1470,26 @@ pub mod pallet {
 				Error::<T>::TooManyTargets
 			);
 
+			let mut targets = targets
+				.into_iter()
+				.map(|t| T::Lookup::lookup(t).map_err(DispatchError::from))
+				.collect::<Result<Vec<_>, _>>()?;
+
+			targets.sort();
+			targets.dedup();
+
 			let old = Nominators::<T>::get(stash).map_or_else(Vec::new, |x| x.targets.into_inner());
 
 			let targets: BoundedVec<_, _> = targets
 				.into_iter()
-				.map(|t| T::Lookup::lookup(t).map_err(DispatchError::from))
 				.map(|n| {
-					n.and_then(|n| {
-						if old.contains(&n) || !Validators::<T>::get(&n).blocked {
-							Ok(n)
-						} else {
-							Err(Error::<T>::BadTarget.into())
-						}
-					})
+					if old.contains(&n) || !Validators::<T>::get(&n).blocked {
+						Ok(n)
+					} else {
+						Err(Error::<T>::BadTarget.into())
+					}
 				})
-				.collect::<Result<Vec<_>, _>>()?
+				.collect::<Result<Vec<_>, DispatchError>>()?
 				.try_into()
 				.map_err(|_| Error::<T>::TooManyNominators)?;
 

substrate/frame/staking/src/tests.rs

@@ -788,6 +788,31 @@ fn nominators_also_get_slashed_pro_rata() {
 		});
 }
 
+#[test]
+fn nominate_same_account_should_be_filtered() {
+	ExtBuilder::default().build_and_execute(|| {
+		let duplicated_targets = vec![11, 21, 31, 11, 21, 31, 11, 11, 21, 21, 31, 31];
+
+		assert_eq!(Staking::nominators(101).unwrap().targets, vec![11, 21]);
+		assert_ok!(Staking::nominate(RuntimeOrigin::signed(101), duplicated_targets.clone()));
+		assert_eq!(Staking::nominators(101).unwrap().targets, vec![11, 21, 31]);
+
+		// Make sure it can correct the wrong automatically.
+		Nominators::<Test>::insert(
+			101,
+			Nominations {
+				targets: BoundedVec::truncate_from(duplicated_targets.clone()),
+				submitted_in: Default::default(),
+				suppressed: Default::default(),
+			},
+		);
+		assert_eq!(Staking::nominators(101).unwrap().targets, duplicated_targets);
+
+		assert_ok!(Staking::nominate(RuntimeOrigin::signed(101), duplicated_targets));
+		assert_eq!(Staking::nominators(101).unwrap().targets, vec![11, 21, 31]);
+	});
+}
+
 #[test]
 fn double_staking_should_fail() {
 	// should test (in the same order):