REVERT ME: demo that Drop impl doesn't work

frame/election-provider-multi-phase/src/benchmarking.rs

@@ -282,7 +282,7 @@ frame_benchmarking::benchmarks! {
 			let signed_submission = SignedSubmission { solution, ..Default::default() };
 			signed_submissions.insert(signed_submission);
 		}
-		signed_submissions.put();
+		drop(signed_submissions);
 
 		let caller = frame_benchmarking::whitelisted_caller();
 		T::Currency::make_free_balance_be(&caller,  T::Currency::minimum_balance() * 10u32.into());

frame/election-provider-multi-phase/src/lib.rs

@@ -900,7 +900,6 @@ pub mod pallet {
 					.map_err(|_| Error::<T>::SignedCannotPayDeposit)?;
 			}
 
-			signed_submissions.put();
 			Self::deposit_event(Event::SolutionStored(ElectionCompute::Signed, ejected_a_solution));
 			Ok(())
 		}

frame/election-provider-multi-phase/src/signed.rs

@@ -123,18 +123,6 @@ impl<T: Config> SignedSubmissions<T> {
 		}
 	}
 
-	/// Put the signed submissions back into storage.
-	pub fn put(self) {
-		SignedSubmissionIndices::<T>::put(self.indices);
-		SignedSubmissionNextIndex::<T>::put(self.next_idx);
-		for key in self.deletion_overlay {
-			SignedSubmissionsMap::<T>::remove(key);
-		}
-		for (key, value) in self.insertion_overlay {
-			SignedSubmissionsMap::<T>::insert(key, value);
-		}
-	}
-
 	/// Get the submission at a particular index.
 	fn map_get(&self, idx: u32) -> Option<SignedSubmissionOf<T>> {
 		self.insertion_overlay
@@ -166,7 +154,7 @@ impl<T: Config> SignedSubmissions<T> {
 	/// arbitrary order
 	pub fn drain(&mut self) -> impl '_ + Iterator<Item = SignedSubmissionOf<T>> {
 		self.indices.clear();
-		SignedSubmissionNextIndex::<T>::kill();
+		self.next_idx = 0;
 		let insertion_overlay = sp_std::mem::take(&mut self.insertion_overlay);
 		SignedSubmissionsMap::<T>::drain()
 			.filter(move |(k, _v)| !self.deletion_overlay.contains(k))
@@ -255,6 +243,20 @@ impl<T: Config> Deref for SignedSubmissions<T> {
 	}
 }
 
+impl<T: Config> Drop for SignedSubmissions<T> {
+    fn drop(&mut self) {
+		SignedSubmissionIndices::<T>::put(sp_std::mem::take(&mut self.indices));
+		SignedSubmissionNextIndex::<T>::put(self.next_idx);
+
+		for key in self.deletion_overlay.iter().copied() {
+			SignedSubmissionsMap::<T>::remove(key);
+		}
+		for (key, value) in sp_std::mem::take(&mut self.insertion_overlay) {
+			SignedSubmissionsMap::<T>::insert(key, value);
+		}
+    }
+}
+
 impl<T: Config> Pallet<T> {
 	/// `Self` accessor for `SignedSubmission<T>`.
 	pub fn signed_submissions() -> SignedSubmissions<T> {
@@ -321,8 +323,6 @@ impl<T: Config> Pallet<T> {
 			debug_assert!(_remaining.is_zero());
 		}
 
-		all_submissions.put();
-
 		log!(debug, "closed signed phase, found solution? {}, discarded {}", found_solution, discarded);
 		(found_solution, weight)
 	}