mutate_exists for StorageValue with ValueQuery (#13245)

* mutate_exists for StorageValue with ValueQuery

Signed-off-by: muraca <mmuraca247@gmail.com>

* added `#[crate::storage_alias]` to tests

Signed-off-by: muraca <mmuraca247@gmail.com>

* added StorageEntryMetadata

Signed-off-by: muraca <mmuraca247@gmail.com>

* Update frame/support/src/lib.rs

---------

Signed-off-by: muraca <mmuraca247@gmail.com>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

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

@@ -118,6 +118,30 @@ impl<T: FullCodec, G: StorageValue<T>> storage::StorageValue<T> for G {
 		ret
 	}
 
+	fn mutate_exists<R, F>(f: F) -> R
+	where
+		F: FnOnce(&mut Option<T>) -> R,
+	{
+		Self::try_mutate_exists(|v| Ok::<R, Never>(f(v)))
+			.expect("`Never` can not be constructed; qed")
+	}
+
+	fn try_mutate_exists<R, E, F>(f: F) -> Result<R, E>
+	where
+		F: FnOnce(&mut Option<T>) -> Result<R, E>,
+	{
+		let mut val = G::from_query_to_optional_value(Self::get());
+
+		let ret = f(&mut val);
+		if ret.is_ok() {
+			match val {
+				Some(ref val) => Self::put(val),
+				None => Self::kill(),
+			}
+		}
+		ret
+	}
+
 	fn take() -> G::Query {
 		let key = Self::storage_value_final_key();
 		let value = unhashed::get(&key);

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

@@ -114,6 +114,12 @@ pub trait StorageValue<T: FullCodec> {
 	/// Mutate the value if closure returns `Ok`
 	fn try_mutate<R, E, F: FnOnce(&mut Self::Query) -> Result<R, E>>(f: F) -> Result<R, E>;
 
+	/// Mutate the value. Deletes the item if mutated to a `None`.
+	fn mutate_exists<R, F: FnOnce(&mut Option<T>) -> R>(f: F) -> R;
+
+	/// Mutate the value if closure returns `Ok`. Deletes the item if mutated to a `None`.
+	fn try_mutate_exists<R, E, F: FnOnce(&mut Option<T>) -> Result<R, E>>(f: F) -> Result<R, E>;
+
 	/// Clear the storage value.
 	fn kill();
 

substrate/frame/support/src/storage/types/value.rs

@@ -142,6 +142,18 @@ where
 		<Self as crate::storage::StorageValue<Value>>::try_mutate(f)
 	}
 
+	/// Mutate the value. Deletes the item if mutated to a `None`.
+	pub fn mutate_exists<R, F: FnOnce(&mut Option<Value>) -> R>(f: F) -> R {
+		<Self as crate::storage::StorageValue<Value>>::mutate_exists(f)
+	}
+
+	/// Mutate the value if closure returns `Ok`. Deletes the item if mutated to a `None`.
+	pub fn try_mutate_exists<R, E, F: FnOnce(&mut Option<Value>) -> Result<R, E>>(
+		f: F,
+	) -> Result<R, E> {
+		<Self as crate::storage::StorageValue<Value>>::try_mutate_exists(f)
+	}
+
 	/// Clear the storage value.
 	pub fn kill() {
 		<Self as crate::storage::StorageValue<Value>>::kill()