From 37ed154535598cc59bc02bb1a14174ca50193eb5 Mon Sep 17 00:00:00 2001
From: Gavin Wood <gavin@parity.io>
Date: Thu, 5 Dec 2019 16:57:25 +0100
Subject: [PATCH] Allow members of groups to change their key (#4300)

---
 substrate/frame/membership/src/lib.rs | 40 ++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/substrate/frame/membership/src/lib.rs b/substrate/frame/membership/src/lib.rs
index d18c107d66..acecd456ee 100644
--- a/substrate/frame/membership/src/lib.rs
+++ b/substrate/frame/membership/src/lib.rs
@@ -28,7 +28,7 @@ use support::{
 	traits::{ChangeMembers, InitializeMembers},
 	weights::SimpleDispatchInfo,
 };
-use system::ensure_root;
+use system::{ensure_root, ensure_signed};
 use sp_runtime::traits::EnsureOrigin;
 
 pub trait Trait<I=DefaultInstance>: system::Trait {
@@ -86,6 +86,8 @@ decl_event!(
 		MembersSwapped,
 		/// The membership was reset; see the transaction for who the new set is.
 		MembersReset,
+		/// One of the members' keys changed.
+		KeyChanged,
 		/// Phantom member, never used.
 		Dummy(rstd::marker::PhantomData<(AccountId, Event)>),
 	}
@@ -186,6 +188,31 @@ decl_module! {
 
 			Self::deposit_event(RawEvent::MembersReset);
 		}
+
+		/// Swap out the sending member for some other key `new`.
+		///
+		/// May only be called from `Signed` origin of a current member.
+		#[weight = SimpleDispatchInfo::FixedNormal(50_000)]
+		fn change_key(origin, new: T::AccountId) {
+			let remove = ensure_signed(origin)?;
+
+			if remove != new {
+				let mut members = <Members<T, I>>::get();
+				let location = members.binary_search(&remove).ok().ok_or("not a member")?;
+				members[location] = new.clone();
+				let _location = members.binary_search(&new).err().ok_or("already a member")?;
+				members.sort();
+				<Members<T, I>>::put(&members);
+
+				T::MembershipChanged::change_members_sorted(
+					&[new],
+					&[remove],
+					&members[..],
+				);
+			}
+
+			Self::deposit_event(RawEvent::KeyChanged);
+		}
 	}
 }
 
@@ -333,6 +360,17 @@ mod tests {
 		});
 	}
 
+	#[test]
+	fn change_key_works() {
+		new_test_ext().execute_with(|| {
+			assert_noop!(Membership::change_key(Origin::signed(3), 25), "not a member");
+			assert_noop!(Membership::change_key(Origin::signed(10), 20), "already a member");
+			assert_ok!(Membership::change_key(Origin::signed(10), 40));
+			assert_eq!(Membership::members(), vec![20, 30, 40]);
+			assert_eq!(MEMBERS.with(|m| m.borrow().clone()), Membership::members());
+		});
+	}
+
 	#[test]
 	fn reset_members_works() {
 		new_test_ext().execute_with(|| {