Extract engines to own crates (#10966)

* Add client-traits crate
Move the BlockInfo trait to new crate

* New crate `machine`
Contains code extracted from ethcore that defines `Machine`, `Externalities` and other execution related code.

* Use new machine and client-traits crates in ethcore

* Use new crates machine and client-traits instead of ethcore where appropriate

* Fix tests

* Don't re-export so many types from ethcore::client

* Fixing more fallout from removing re-export

* fix test

* More fallout from not re-exporting types

* Add some docs

* cleanup

* import the macro edition style

* Tweak docs

* Add missing import

* remove unused ethabi_derive imports

* Use latest ethabi-contract

* Move many traits from ethcore/client/traits to client-traits crate
Initial version of extracted Engine trait

* Move snapshot related traits to the engine crate (eew)

* Move a few snapshot related types to common_types
Cleanup Executed as exported from machine crate

* fix warning

* Gradually introduce new engine crate: snapshot

* ethcore typechecks with new engine crate

* Sort out types outside ethcore

* Add an EpochVerifier to ethash and use that in Engine.epoch_verifier()
Cleanup

* Document pub members

* Sort out tests
Sort out default impls for EpochVerifier

* Add test-helpers feature and move EngineSigner impl to the right place

* Sort out tests

* Sort out tests and refactor verification types

* Fix missing traits

* More missing traits
Fix Histogram

* Fix tests and cleanup

* cleanup

* Put back needed logger import

* Don't rexport common_types from ethcore/src/client
Don't export ethcore::client::*

* Remove files no longer used
Use types from the engine crate
Explicit exports from engine::engine

* Get rid of itertools

* Move a few more traits from ethcore to client-traits: BlockChainReset, ScheduleInfo, StateClient

* Move ProvingBlockChainClient to client-traits

* Don't re-export ForkChoice and Transition from ethcore

* Address grumbles: sort imports, remove commented out code

* Fix merge resolution error

* Extract the Clique engine to own crate

* Extract NullEngine and the block_reward module from ethcore

* Extract InstantSeal engine to own crate

* Extract remaining engines

* Extract executive_state to own crate so it can be used by engine crates

* Remove snapshot stuff from the engine crate

* Put snapshot traits back in ethcore

* cleanup

* Remove stuff from ethcore

* Don't use itertools

* itertools in aura is legit-ish

* More post-merge fixes

* Re-export less types in client

* cleanup

* Update ethcore/block-reward/Cargo.toml

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update ethcore/engines/basic-authority/Cargo.toml

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update ethcore/engines/ethash/Cargo.toml

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update ethcore/engines/clique/src/lib.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* signers is already a ref

* Add an EngineType enum to tighten up Engine.name()

* Introduce Snapshotting enum to distinguish the type of snapshots a chain uses

* Rename supports_warp to snapshot_mode

* Missing import

* Update ethcore/src/snapshot/consensus/mod.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* remove double-semicolons

ethcore/engine/src/engine.rs

@@ -31,6 +31,7 @@ use common_types::{
 		machine::{AuxiliaryData, AuxiliaryRequest},
 	},
 	errors::{EthcoreError as Error, EngineError},
+	snapshot::Snapshotting,
 	transaction::{self, UnverifiedTransaction},
 };
 use client_traits::EngineClient;
@@ -43,10 +44,7 @@ use machine::{
 };
 use vm::{EnvInfo, Schedule, CallType, ActionValue};
 
-use crate::{
-	signer::EngineSigner,
-	snapshot::SnapshotComponents,
-};
+use crate::signer::EngineSigner;
 
 /// A system-calling closure. Enacts calls on a block's state from the system address.
 pub type SystemCall<'a> = dyn FnMut(Address, Vec<u8>) -> Result<Vec<u8>, String> + 'a;
@@ -306,16 +304,8 @@ pub trait Engine: Sync + Send {
 	/// Trigger next step of the consensus engine.
 	fn step(&self) {}
 
-	/// Create a factory for building snapshot chunks and restoring from them.
-	/// Returning `None` indicates that this engine doesn't support snapshot creation.
-	fn snapshot_components(&self) -> Option<Box<dyn SnapshotComponents>> {
-		None
-	}
-
-	/// Whether this engine supports warp sync.
-	fn supports_warp(&self) -> bool {
-		self.snapshot_components().is_some()
-	}
+	/// Snapshot mode for the engine: Unsupported, PoW or PoA
+	fn snapshot_mode(&self) -> Snapshotting { Snapshotting::Unsupported }
 
 	/// Return a new open block header timestamp based on the parent timestamp.
 	fn open_block_header_timestamp(&self, parent_timestamp: u64) -> u64 {

ethcore/engine/src/lib.rs

@@ -18,7 +18,6 @@
 
 mod engine;
 pub mod signer;
-pub mod snapshot;
 
 pub use crate::engine::{
 	Engine,