Introduce default-setting prime for collective (#5137)

* Introduce default-setting prime for collective

* Docs.

* Elections phragmen supports prime

* Fix

* Membership supports prime

* Fix

* Update frame/collective/src/lib.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

substrate/frame/support/src/storage/generator/value.rs

@@ -91,6 +91,14 @@ impl<T: FullCodec, G: StorageValue<T>> storage::StorageValue<T> for G {
 		unhashed::put(&Self::storage_value_final_key(), &val)
 	}
 
+	fn set(maybe_val: Self::Query) {
+		if let Some(val) = G::from_query_to_optional_value(maybe_val) {
+			unhashed::put(&Self::storage_value_final_key(), &val)
+		} else {
+			unhashed::kill(&Self::storage_value_final_key())
+		}
+	}
+
 	fn kill() {
 		unhashed::kill(&Self::storage_value_final_key())
 	}

substrate/frame/support/src/storage/mod.rs

@@ -73,6 +73,10 @@ pub trait StorageValue<T: FullCodec> {
 	/// Store a value under this key into the provided storage instance.
 	fn put<Arg: EncodeLike<T>>(val: Arg);
 
+	/// Store a value under this key into the provided storage instance; this uses the query
+	/// type rather than the underlying value.
+	fn set(val: Self::Query);
+
 	/// Mutate the value
 	fn mutate<R, F: FnOnce(&mut Self::Query) -> R>(f: F) -> R;
 

substrate/frame/support/src/traits.rs

@@ -808,6 +808,8 @@ impl WithdrawReasons {
 pub trait ChangeMembers<AccountId: Clone + Ord> {
 	/// A number of members `incoming` just joined the set and replaced some `outgoing` ones. The
 	/// new set is given by `new`, and need not be sorted.
+	///
+	/// This resets any previous value of prime.
 	fn change_members(incoming: &[AccountId], outgoing: &[AccountId], mut new: Vec<AccountId>) {
 		new.sort_unstable();
 		Self::change_members_sorted(incoming, outgoing, &new[..]);
@@ -817,6 +819,8 @@ pub trait ChangeMembers<AccountId: Clone + Ord> {
 	/// new set is thus given by `sorted_new` and **must be sorted**.
 	///
 	/// NOTE: This is the only function that needs to be implemented in `ChangeMembers`.
+	///
+	/// This resets any previous value of prime.
 	fn change_members_sorted(
 		incoming: &[AccountId],
 		outgoing: &[AccountId],
@@ -825,6 +829,8 @@ pub trait ChangeMembers<AccountId: Clone + Ord> {
 
 	/// Set the new members; they **must already be sorted**. This will compute the diff and use it to
 	/// call `change_members_sorted`.
+	///
+	/// This resets any previous value of prime.
 	fn set_members_sorted(new_members: &[AccountId], old_members: &[AccountId]) {
 		let (incoming, outgoing) = Self::compute_members_diff(new_members, old_members);
 		Self::change_members_sorted(&incoming[..], &outgoing[..], &new_members);
@@ -865,14 +871,20 @@ pub trait ChangeMembers<AccountId: Clone + Ord> {
 		}
 		(incoming, outgoing)
 	}
+
+	/// Set the prime member.
+	fn set_prime(_prime: Option<AccountId>) {}
 }
 
 impl<T: Clone + Ord> ChangeMembers<T> for () {
 	fn change_members(_: &[T], _: &[T], _: Vec<T>) {}
 	fn change_members_sorted(_: &[T], _: &[T], _: &[T]) {}
 	fn set_members_sorted(_: &[T], _: &[T]) {}
+	fn set_prime(_: Option<T>) {}
 }
 
+
+
 /// Trait for type that can handle the initialization of account IDs at genesis.
 pub trait InitializeMembers<AccountId> {
 	/// Initialize the members to the given `members`.