Repot frame_support::traits; introduce some new currency stuff (#8435)

* Reservable, Transferrable Fungible(s), plus adapters.

* Repot into new dir

* Imbalances for Fungibles

* Repot and balanced fungible.

* Clean up names and bridge-over Imbalanced.

* Repot frame_support::trait. Finally.

* Make build.

* Docs

* Good errors

* Fix tests. Implement fungible::Inspect for Balances.

* Implement additional traits for Balances.

* Revert UI test "fixes"

* Fix UI error

* Fix UI test

* Fixes

* Update lock

* Grumbles

* Grumbles

* Fixes

Co-authored-by: Bastian Köcher <info@kchr.de>

substrate/frame/support/src/traits/stored_map.rs

@@ -0,0 +1,141 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2019-2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Traits and associated datatypes for managing abstract stored values.
+
+use codec::FullCodec;
+use sp_runtime::traits::StoredMapError;
+use crate::storage::StorageMap;
+use crate::traits::misc::HandleLifetime;
+
+/// An abstraction of a value stored within storage, but possibly as part of a larger composite
+/// item.
+pub trait StoredMap<K, T: Default> {
+	/// Get the item, or its default if it doesn't yet exist; we make no distinction between the
+	/// two.
+	fn get(k: &K) -> T;
+
+	/// Maybe mutate the item only if an `Ok` value is returned from `f`. Do nothing if an `Err` is
+	/// returned. It is removed or reset to default value if it has been mutated to `None`
+	fn try_mutate_exists<R, E: From<StoredMapError>>(
+		k: &K,
+		f: impl FnOnce(&mut Option<T>) -> Result<R, E>,
+	) -> Result<R, E>;
+
+	// Everything past here has a default implementation.
+
+	/// Mutate the item.
+	fn mutate<R>(k: &K, f: impl FnOnce(&mut T) -> R) -> Result<R, StoredMapError> {
+		Self::mutate_exists(k, |maybe_account| match maybe_account {
+			Some(ref mut account) => f(account),
+			x @ None => {
+				let mut account = Default::default();
+				let r = f(&mut account);
+				*x = Some(account);
+				r
+			}
+		})
+	}
+
+	/// Mutate the item, removing or resetting to default value if it has been mutated to `None`.
+	///
+	/// This is infallible as long as the value does not get destroyed.
+	fn mutate_exists<R>(
+		k: &K,
+		f: impl FnOnce(&mut Option<T>) -> R,
+	) -> Result<R, StoredMapError> {
+		Self::try_mutate_exists(k, |x| -> Result<R, StoredMapError> { Ok(f(x)) })
+	}
+
+	/// Set the item to something new.
+	fn insert(k: &K, t: T) -> Result<(), StoredMapError> { Self::mutate(k, |i| *i = t) }
+
+	/// Remove the item or otherwise replace it with its default value; we don't care which.
+	fn remove(k: &K) -> Result<(), StoredMapError> { Self::mutate_exists(k, |x| *x = None) }
+}
+
+/// A shim for placing around a storage item in order to use it as a `StoredValue`. Ideally this
+/// wouldn't be needed as `StorageValue`s should blanket implement `StoredValue`s, however this
+/// would break the ability to have custom impls of `StoredValue`. The other workaround is to
+/// implement it directly in the macro.
+///
+/// This form has the advantage that two additional types are provides, `Created` and `Removed`,
+/// which are both generic events that can be tied to handlers to do something in the case of being
+/// about to create an account where one didn't previously exist (at all; not just where it used to
+/// be the default value), or where the account is being removed or reset back to the default value
+/// where previously it did exist (though may have been in a default state). This works well with
+/// system module's `CallOnCreatedAccount` and `CallKillAccount`.
+pub struct StorageMapShim<S, L, K, T>(sp_std::marker::PhantomData<(S, L, K, T)>);
+impl<
+	S: StorageMap<K, T, Query=T>,
+	L: HandleLifetime<K>,
+	K: FullCodec,
+	T: FullCodec + Default,
+> StoredMap<K, T> for StorageMapShim<S, L, K, T> {
+	fn get(k: &K) -> T { S::get(k) }
+	fn insert(k: &K, t: T) -> Result<(), StoredMapError> {
+		if !S::contains_key(&k) {
+			L::created(k)?;
+		}
+		S::insert(k, t);
+		Ok(())
+	}
+	fn remove(k: &K) -> Result<(), StoredMapError> {
+		if S::contains_key(&k) {
+			L::killed(&k)?;
+			S::remove(k);
+		}
+		Ok(())
+	}
+	fn mutate<R>(k: &K, f: impl FnOnce(&mut T) -> R) -> Result<R, StoredMapError> {
+		if !S::contains_key(&k) {
+			L::created(k)?;
+		}
+		Ok(S::mutate(k, f))
+	}
+	fn mutate_exists<R>(k: &K, f: impl FnOnce(&mut Option<T>) -> R) -> Result<R, StoredMapError> {
+		S::try_mutate_exists(k, |maybe_value| {
+			let existed = maybe_value.is_some();
+			let r = f(maybe_value);
+			let exists = maybe_value.is_some();
+
+			if !existed && exists {
+				L::created(k)?;
+			} else if existed && !exists {
+				L::killed(k)?;
+			}
+			Ok(r)
+		})
+	}
+	fn try_mutate_exists<R, E: From<StoredMapError>>(
+		k: &K,
+		f: impl FnOnce(&mut Option<T>) -> Result<R, E>,
+	) -> Result<R, E> {
+		S::try_mutate_exists(k, |maybe_value| {
+			let existed = maybe_value.is_some();
+			let r = f(maybe_value)?;
+			let exists = maybe_value.is_some();
+
+			if !existed && exists {
+				L::created(k).map_err(E::from)?;
+			} else if existed && !exists {
+				L::killed(k).map_err(E::from)?;
+			}
+			Ok(r)
+		})
+	}
+}