Redesign Democracy pallet (#5294)

* Repot a bit of democracy code

* Basic logic is drafted

* Lazy democracy builds.

* Add non-locked split-voting and instant-scheduling.

* Introduce delegation that works.

* Builds again.

* Indentation

* Building.

* Docs and migration

* Fix half of the tests

* Fix up & repot tests

* Fix runtime build

* Update docs

* Docs

* Nits.

* Turnout counts full capital

* Delegations could towards capital

* proxy delegation & proxy unvoting

* Fix

* Tests for split-voting

* Add missing file

* Persistent locking.

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

@@ -19,6 +19,7 @@
 use sp_std::prelude::*;
 use codec::{Encode, Decode};
 use crate::{StorageHasher, Twox128};
+use crate::hash::ReversibleStorageHasher;
 
 /// Utility to iterate through raw items in storage.
 pub struct StorageIterator<T> {
@@ -78,6 +79,72 @@ impl<T: Decode + Sized> Iterator for StorageIterator<T> {
 	}
 }
 
+/// Utility to iterate through raw items in storage.
+pub struct StorageKeyIterator<K, T, H: ReversibleStorageHasher> {
+	prefix: Vec<u8>,
+	previous_key: Vec<u8>,
+	drain: bool,
+	_phantom: ::sp_std::marker::PhantomData<(K, T, H)>,
+}
+
+impl<K, T, H: ReversibleStorageHasher> StorageKeyIterator<K, T, H> {
+	/// Construct iterator to iterate over map items in `module` for the map called `item`.
+	pub fn new(module: &[u8], item: &[u8]) -> Self {
+		Self::with_suffix(module, item, &[][..])
+	}
+
+	/// Construct iterator to iterate over map items in `module` for the map called `item`.
+	pub fn with_suffix(module: &[u8], item: &[u8], suffix: &[u8]) -> Self {
+		let mut prefix = Vec::new();
+		prefix.extend_from_slice(&Twox128::hash(module));
+		prefix.extend_from_slice(&Twox128::hash(item));
+		prefix.extend_from_slice(suffix);
+		let previous_key = prefix.clone();
+		Self { prefix, previous_key, drain: false, _phantom: Default::default() }
+	}
+
+	/// Mutate this iterator into a draining iterator; items iterated are removed from storage.
+	pub fn drain(mut self) -> Self {
+		self.drain = true;
+		self
+	}
+}
+
+impl<K: Decode + Sized, T: Decode + Sized, H: ReversibleStorageHasher> Iterator
+	for StorageKeyIterator<K, T, H>
+{
+	type Item = (K, T);
+
+	fn next(&mut self) -> Option<(K, T)> {
+		loop {
+			let maybe_next = sp_io::storage::next_key(&self.previous_key)
+				.filter(|n| n.starts_with(&self.prefix));
+			break match maybe_next {
+				Some(next) => {
+					self.previous_key = next.clone();
+					let mut key_material = H::reverse(&next[self.prefix.len()..]);
+					match K::decode(&mut key_material) {
+						Ok(key) => {
+							let maybe_value = frame_support::storage::unhashed::get::<T>(&next);
+							match maybe_value {
+								Some(value) => {
+									if self.drain {
+										frame_support::storage::unhashed::kill(&next);
+									}
+									Some((key, value))
+								}
+								None => continue,
+							}
+						}
+						Err(_) => continue,
+					}
+				}
+				None => None,
+			}
+		}
+	}
+}
+
 /// Get a particular value in storage by the `module`, the map's `item` name and the key `hash`.
 pub fn have_storage_value(module: &[u8], item: &[u8], hash: &[u8]) -> bool {
 	get_storage_value::<()>(module, item, hash).is_some()
@@ -109,3 +176,12 @@ pub fn put_storage_value<T: Encode>(module: &[u8], item: &[u8], hash: &[u8], val
 	key[32..].copy_from_slice(hash);
 	frame_support::storage::unhashed::put(&key, &value);
 }
+
+/// Get a particular value in storage by the `module`, the map's `item` name and the key `hash`.
+pub fn remove_storage_prefix(module: &[u8], item: &[u8], hash: &[u8]) {
+	let mut key = vec![0u8; 32 + hash.len()];
+	key[0..16].copy_from_slice(&Twox128::hash(module));
+	key[16..32].copy_from_slice(&Twox128::hash(item));
+	key[32..].copy_from_slice(hash);
+	frame_support::storage::unhashed::kill_prefix(&key)
+}