Introduces account existence providers reference counting (#7363)

* Initial draft

* Latest changes

* Final bits.

* Fixes

* Fixes

* Test fixes

* Fix tests

* Fix babe tests

* Fix

* Fix

* Fix

* Fix

* Fix

* fix warnings in assets

* Fix UI tests

* fix line width

* Fix

* Update frame/system/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update frame/system/src/lib.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Fix

* fix unused warnings

* Fix

* Update frame/system/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Update frame/system/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fix

* fix slash and comprehensive slash test

* fix reserved slash and comprehensive tests

* check slash on non-existent account

* Revert "Fix UI tests"

This reverts commit e0002c0f13442f7d0c95a054a6c515536328a4a0.

* Fix

* Fix utility tests

* keep dispatch error backwards compatible

* Fix

* Fix

* fix ui test

* Companion checker shouldn't be so anal.

* Fix

* Fix

* Fix

* Apply suggestions from code review

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* Update frame/balances/src/lib.rs

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

* return correct slash info when failing gracefully

* fix missing import

* Update frame/system/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fix

* Update frame/balances/src/tests_local.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* Fixes

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

substrate/frame/staking/src/lib.rs

@@ -1222,6 +1222,8 @@ decl_error! {
 		IncorrectHistoryDepth,
 		/// Incorrect number of slashing spans provided.
 		IncorrectSlashingSpans,
+		/// Internal state has become somehow corrupted and the operation cannot continue.
+		BadState,
 	}
 }
 
@@ -1423,13 +1425,13 @@ decl_module! {
 				Err(Error::<T>::InsufficientValue)?
 			}
 
+			system::Module::<T>::inc_consumers(&stash).map_err(|_| Error::<T>::BadState)?;
+
 			// You're auto-bonded forever, here. We might improve this by only bonding when
 			// you actually validate/nominate and remove once you unbond __everything__.
 			<Bonded<T>>::insert(&stash, &controller);
 			<Payee<T>>::insert(&stash, payee);
 
-			system::Module::<T>::inc_ref(&stash);
-
 			let current_era = CurrentEra::get().unwrap_or(0);
 			let history_depth = Self::history_depth();
 			let last_reward_era = current_era.saturating_sub(history_depth);
@@ -2028,9 +2030,9 @@ decl_module! {
 			}
 		}
 
-		/// Remove all data structure concerning a staker/stash once its balance is zero.
+		/// Remove all data structure concerning a staker/stash once its balance is at the minimum.
 		/// This is essentially equivalent to `withdraw_unbonded` except it can be called by anyone
-		/// and the target `stash` must have no funds left.
+		/// and the target `stash` must have no funds left beyond the ED.
 		///
 		/// This can be called from any origin.
 		///
@@ -2045,7 +2047,8 @@ decl_module! {
 		/// # </weight>
 		#[weight = T::WeightInfo::reap_stash(*num_slashing_spans)]
 		fn reap_stash(_origin, stash: T::AccountId, num_slashing_spans: u32) {
-			ensure!(T::Currency::total_balance(&stash).is_zero(), Error::<T>::FundedTarget);
+			let at_minimum = T::Currency::total_balance(&stash) == T::Currency::minimum_balance();
+			ensure!(at_minimum, Error::<T>::FundedTarget);
 			Self::kill_stash(&stash, num_slashing_spans)?;
 			T::Currency::remove_lock(STAKING_ID, &stash);
 		}
@@ -3007,7 +3010,7 @@ impl<T: Config> Module<T> {
 		<Validators<T>>::remove(stash);
 		<Nominators<T>>::remove(stash);
 
-		system::Module::<T>::dec_ref(stash);
+		system::Module::<T>::dec_consumers(stash);
 
 		Ok(())
 	}