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/validation.rs

@@ -0,0 +1,242 @@
+// 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 for dealing with validation and validators.
+
+use sp_std::prelude::*;
+use codec::{Codec, Decode};
+use sp_runtime::traits::{Convert, Zero};
+use sp_runtime::{BoundToRuntimeAppPublic, ConsensusEngineId, Percent, RuntimeAppPublic};
+use sp_staking::SessionIndex;
+use crate::dispatch::Parameter;
+use crate::weights::Weight;
+
+/// A trait for online node inspection in a session.
+///
+/// Something that can give information about the current validator set.
+pub trait ValidatorSet<AccountId> {
+	/// Type for representing validator id in a session.
+	type ValidatorId: Parameter;
+	/// A type for converting `AccountId` to `ValidatorId`.
+	type ValidatorIdOf: Convert<AccountId, Option<Self::ValidatorId>>;
+
+	/// Returns current session index.
+	fn session_index() -> SessionIndex;
+
+	/// Returns the active set of validators.
+	fn validators() -> Vec<Self::ValidatorId>;
+}
+
+/// [`ValidatorSet`] combined with an identification.
+pub trait ValidatorSetWithIdentification<AccountId>: ValidatorSet<AccountId> {
+	/// Full identification of `ValidatorId`.
+	type Identification: Parameter;
+	/// A type for converting `ValidatorId` to `Identification`.
+	type IdentificationOf: Convert<Self::ValidatorId, Option<Self::Identification>>;
+}
+
+/// A trait for finding the author of a block header based on the `PreRuntime` digests contained
+/// within it.
+pub trait FindAuthor<Author> {
+	/// Find the author of a block based on the pre-runtime digests.
+	fn find_author<'a, I>(digests: I) -> Option<Author>
+		where I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>;
+}
+
+impl<A> FindAuthor<A> for () {
+	fn find_author<'a, I>(_: I) -> Option<A>
+		where I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>
+	{
+		None
+	}
+}
+
+/// A trait for verifying the seal of a header and returning the author.
+pub trait VerifySeal<Header, Author> {
+	/// Verify a header and return the author, if any.
+	fn verify_seal(header: &Header) -> Result<Option<Author>, &'static str>;
+}
+
+/// A session handler for specific key type.
+pub trait OneSessionHandler<ValidatorId>: BoundToRuntimeAppPublic {
+	/// The key type expected.
+	type Key: Decode + Default + RuntimeAppPublic;
+
+	/// The given validator set will be used for the genesis session.
+	/// It is guaranteed that the given validator set will also be used
+	/// for the second session, therefore the first call to `on_new_session`
+	/// should provide the same validator set.
+	fn on_genesis_session<'a, I: 'a>(validators: I)
+		where I: Iterator<Item=(&'a ValidatorId, Self::Key)>, ValidatorId: 'a;
+
+	/// Session set has changed; act appropriately. Note that this can be called
+	/// before initialization of your module.
+	///
+	/// `changed` is true when at least one of the session keys
+	/// or the underlying economic identities/distribution behind one the
+	/// session keys has changed, false otherwise.
+	///
+	/// The `validators` are the validators of the incoming session, and `queued_validators`
+	/// will follow.
+	fn on_new_session<'a, I: 'a>(
+		changed: bool,
+		validators: I,
+		queued_validators: I,
+	) where I: Iterator<Item=(&'a ValidatorId, Self::Key)>, ValidatorId: 'a;
+
+	/// A notification for end of the session.
+	///
+	/// Note it is triggered before any `SessionManager::end_session` handlers,
+	/// so we can still affect the validator set.
+	fn on_before_session_ending() {}
+
+	/// A validator got disabled. Act accordingly until a new session begins.
+	fn on_disabled(_validator_index: usize);
+}
+
+/// Something that can estimate at which block the next session rotation will happen (i.e. a new
+/// session starts).
+///
+/// The accuracy of the estimates is dependent on the specific implementation, but in order to get
+/// the best estimate possible these methods should be called throughout the duration of the session
+/// (rather than calling once and storing the result).
+///
+/// This should be the same logical unit that dictates `ShouldEndSession` to the session module. No
+/// assumptions are made about the scheduling of the sessions.
+pub trait EstimateNextSessionRotation<BlockNumber> {
+	/// Return the average length of a session.
+	///
+	/// This may or may not be accurate.
+	fn average_session_length() -> BlockNumber;
+
+	/// Return an estimate of the current session progress.
+	///
+	/// None should be returned if the estimation fails to come to an answer.
+	fn estimate_current_session_progress(now: BlockNumber) -> (Option<Percent>, Weight);
+
+	/// Return the block number at which the next session rotation is estimated to happen.
+	///
+	/// None should be returned if the estimation fails to come to an answer.
+	fn estimate_next_session_rotation(now: BlockNumber) -> (Option<BlockNumber>, Weight);
+}
+
+impl<BlockNumber: Zero> EstimateNextSessionRotation<BlockNumber> for () {
+	fn average_session_length() -> BlockNumber {
+		Zero::zero()
+	}
+
+	fn estimate_current_session_progress(_: BlockNumber) -> (Option<Percent>, Weight) {
+		(None, Zero::zero())
+	}
+
+	fn estimate_next_session_rotation(_: BlockNumber) -> (Option<BlockNumber>, Weight) {
+		(None, Zero::zero())
+	}
+}
+
+/// Something that can estimate at which block scheduling of the next session will happen (i.e when
+/// we will try to fetch new validators).
+///
+/// This only refers to the point when we fetch the next session details and not when we enact them
+/// (for enactment there's `EstimateNextSessionRotation`). With `pallet-session` this should be
+/// triggered whenever `SessionManager::new_session` is called.
+///
+/// For example, if we are using a staking module this would be the block when the session module
+/// would ask staking what the next validator set will be, as such this must always be implemented
+/// by the session module.
+pub trait EstimateNextNewSession<BlockNumber> {
+	/// Return the average length of a session.
+	///
+	/// This may or may not be accurate.
+	fn average_session_length() -> BlockNumber;
+
+	/// Return the block number at which the next new session is estimated to happen.
+	///
+	/// None should be returned if the estimation fails to come to an answer.
+	fn estimate_next_new_session(_: BlockNumber) -> (Option<BlockNumber>, Weight);
+}
+
+impl<BlockNumber: Zero> EstimateNextNewSession<BlockNumber> for () {
+	fn average_session_length() -> BlockNumber {
+		Zero::zero()
+	}
+
+	fn estimate_next_new_session(_: BlockNumber) -> (Option<BlockNumber>, Weight) {
+		(None, Zero::zero())
+	}
+}
+
+/// Something which can compute and check proofs of
+/// a historical key owner and return full identification data of that
+/// key owner.
+pub trait KeyOwnerProofSystem<Key> {
+	/// The proof of membership itself.
+	type Proof: Codec;
+	/// The full identification of a key owner and the stash account.
+	type IdentificationTuple: Codec;
+
+	/// Prove membership of a key owner in the current block-state.
+	///
+	/// This should typically only be called off-chain, since it may be
+	/// computationally heavy.
+	///
+	/// Returns `Some` iff the key owner referred to by the given `key` is a
+	/// member of the current set.
+	fn prove(key: Key) -> Option<Self::Proof>;
+
+	/// Check a proof of membership on-chain. Return `Some` iff the proof is
+	/// valid and recent enough to check.
+	fn check_proof(key: Key, proof: Self::Proof) -> Option<Self::IdentificationTuple>;
+}
+
+impl<Key> KeyOwnerProofSystem<Key> for () {
+	// The proof and identification tuples is any bottom type to guarantee that the methods of this
+	// implementation can never be called or return anything other than `None`.
+	type Proof = crate::Void;
+	type IdentificationTuple = crate::Void;
+
+	fn prove(_key: Key) -> Option<Self::Proof> {
+		None
+	}
+
+	fn check_proof(_key: Key, _proof: Self::Proof) -> Option<Self::IdentificationTuple> {
+		None
+	}
+}
+
+/// Trait to be used by block producing consensus engine modules to determine
+/// how late the current block is (e.g. in a slot-based proposal mechanism how
+/// many slots were skipped since the previous block).
+pub trait Lateness<N> {
+	/// Returns a generic measure of how late the current block is compared to
+	/// its parent.
+	fn lateness(&self) -> N;
+}
+
+impl<N: Zero> Lateness<N> for () {
+	fn lateness(&self) -> N {
+		Zero::zero()
+	}
+}
+
+/// Implementors of this trait provide information about whether or not some validator has
+/// been registered with them. The [Session module](../../pallet_session/index.html) is an implementor.
+pub trait ValidatorRegistration<ValidatorId> {
+	/// Returns true if the provided validator ID has been registered with the implementing runtime
+	/// module
+	fn is_registered(id: &ValidatorId) -> bool;
+}