Add swap and decode_len to DoubleMap finishing #3749 (#4264)

* Add `swap` and `decode_len` to `DoubleMap`

*  Add tests to `swap` and `decode_len` for `DoubleMap` (WIP)

* Address review comments

* Remove function that is not in scope

* fix test

* better naming

substrate/frame/support/src/lib.rs

@@ -292,6 +292,36 @@ mod tests {
 		});
 	}
 
+	#[test]
+	fn double_map_swap_works() {
+		new_test_ext().execute_with(|| {
+			DataDM::insert(0, 1, 1);
+			DataDM::insert(1, 0, 2);
+			DataDM::insert(1, 1, 3);
+
+			let get_all = || vec![
+				DataDM::get(0, 1),
+				DataDM::get(1, 0),
+				DataDM::get(1, 1),
+				DataDM::get(2, 0),
+				DataDM::get(2, 1),
+			];
+			assert_eq!(get_all(), vec![1, 2, 3, 0, 0]);
+
+			// Two existing
+			DataDM::swap(0, 1, 1, 0);
+			assert_eq!(get_all(), vec![2, 1, 3, 0, 0]);
+
+			// Left existing
+			DataDM::swap(1, 0, 2, 0);
+			assert_eq!(get_all(), vec![2, 0, 3, 1, 0]);
+
+			// Right existing
+			DataDM::swap(2, 1, 1, 1);
+			assert_eq!(get_all(), vec![2, 0, 0, 1, 3]);
+		});
+	}
+
 	#[test]
 	fn linked_map_basic_insert_remove_should_work() {
 		new_test_ext().execute_with(|| {

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

@@ -17,7 +17,7 @@
 use rstd::prelude::*;
 use rstd::borrow::Borrow;
 use codec::{Ref, FullCodec, FullEncode, Encode, EncodeLike, EncodeAppend};
-use crate::{storage::{self, unhashed}, hash::{StorageHasher, Twox128}};
+use crate::{storage::{self, unhashed}, hash::{StorageHasher, Twox128}, traits::Len};
 
 /// Generator for `StorageDoubleMap` used by `decl_storage`.
 ///
@@ -137,6 +137,29 @@ where
 		G::from_optional_value_to_query(value)
 	}
 
+	fn swap<XKArg1, XKArg2, YKArg1, YKArg2>(x_k1: XKArg1, x_k2: XKArg2, y_k1: YKArg1, y_k2: YKArg2)
+	where
+		XKArg1: EncodeLike<K1>,
+		XKArg2: EncodeLike<K2>,
+		YKArg1: EncodeLike<K1>,
+		YKArg2: EncodeLike<K2>
+	{
+		let final_x_key = Self::storage_double_map_final_key(x_k1, x_k2);
+		let final_y_key = Self::storage_double_map_final_key(y_k1, y_k2);
+
+		let v1 = unhashed::get_raw(&final_x_key);
+		if let Some(val) = unhashed::get_raw(&final_y_key) {
+			unhashed::put_raw(&final_x_key, &val);
+		} else {
+			unhashed::kill(&final_x_key)
+		}
+		if let Some(val) = v1 {
+			unhashed::put_raw(&final_y_key, &val);
+		} else {
+			unhashed::kill(&final_y_key)
+		}
+	}
+
 	fn insert<KArg1, KArg2, VArg>(k1: KArg1, k2: KArg2, val: VArg)
 	where
 		KArg1: EncodeLike<K1>,
@@ -225,4 +248,21 @@ where
 		Self::append(Ref::from(&k1), Ref::from(&k2), items.clone())
 			.unwrap_or_else(|_| Self::insert(k1, k2, items));
 	}
+
+	fn decode_len<KArg1, KArg2>(key1: KArg1, key2: KArg2) -> Result<usize, &'static str>
+		where KArg1: EncodeLike<K1>,
+		      KArg2: EncodeLike<K2>,
+		      V: codec::DecodeLength + Len,
+	{
+		let final_key = Self::storage_double_map_final_key(key1, key2);
+		if let Some(v) = unhashed::get_raw(&final_key) {
+			<V as codec::DecodeLength>::len(&v).map_err(|e| e.what())
+		} else {
+			let len = G::from_query_to_optional_value(G::from_optional_value_to_query(None))
+				.map(|v| v.len())
+				.unwrap_or(0);
+
+			Ok(len)
+		}
+	}
 }

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

@@ -284,6 +284,14 @@ pub trait StorageDoubleMap<K1: FullEncode, K2: FullEncode, V: FullCodec> {
 		KArg1: EncodeLike<K1>,
 		KArg2: EncodeLike<K2>;
 
+	/// Swap the values of two key-pairs.
+	fn swap<XKArg1, XKArg2, YKArg1, YKArg2>(x_k1: XKArg1, x_k2: XKArg2, y_k1: YKArg1, y_k2: YKArg2)
+	where
+		XKArg1: EncodeLike<K1>,
+		XKArg2: EncodeLike<K2>,
+		YKArg1: EncodeLike<K1>,
+		YKArg2: EncodeLike<K2>;
+
 	fn insert<KArg1, KArg2, VArg>(k1: KArg1, k2: KArg2, val: VArg)
 	where
 		KArg1: EncodeLike<K1>,
@@ -330,4 +338,17 @@ pub trait StorageDoubleMap<K1: FullEncode, K2: FullEncode, V: FullCodec> {
 		V: EncodeAppend<Item=Item>,
 		Items: IntoIterator<Item=EncodeLikeItem> + Clone + EncodeLike<V>,
 		Items::IntoIter: ExactSizeIterator;
+
+	/// Read the length of the value in a fast way, without decoding the entire value.
+	///
+	/// `V` is required to implement `Codec::DecodeLength`.
+	///
+	/// Note that `0` is returned as the default value if no encoded value exists at the given key.
+	/// Therefore, this function cannot be used as a sign of _existence_. use the `::exists()`
+	/// function for this purpose.
+	fn decode_len<KArg1, KArg2>(key1: KArg1, key2: KArg2) -> Result<usize, &'static str>
+		where
+			KArg1: EncodeLike<K1>,
+			KArg2: EncodeLike<K2>,
+			V: codec::DecodeLength + Len;
 }