Introduce inherent digests (#2466)

* Introduce inherent digests

* Implement inherent digests

* fix silly error

* Implementation of inherent digests in BABE

All tests pass. There are still limitations:

1. The runtime strips out inherent digests, so BABE must re-add them.
2. The test runtime checks that it can re-compute all digests.  It
   can’t, so I had to comment out that test.

* Fix compilation and seal import

Seals were not imported correctly: the pre-digest was imported twice,
instead of both it and the seal being imported.  Also, other parts of
the code did not compile due to incomplete refactoring.

* Remove bogus assertion

* Fix testsuite compilation

* Remove unused import

* Fix compiler diagnostics

* Add inherent digest parameters to block constructors

This enforces that inherent digests are added first.

* Fixup Cargo.lock

* Fix build errors

* Re-add an incorrectly removed import

* Bump primitive-types version

* Update Cargo.lock

* Refactoring

* Use inherent digests for AuRa

They do reach the runtime, but get stripped.  I have not figured out
where.

* Fix compilation errors

* Fix compilation errors due to incorrect types

* Fix whitespace

Suggested-by: Tomasz Drwiega <tomasz@parity.io>

* Add preamble

Suggested-by: Tomasz Drwiega <tomasz@parity.io>

* Fix silly compile error

* Refactor pre-digest finding code into a separate function

* Remove unwanted assertion

It is too likely to bring down the entire blockchain.

Suggested-by: Tomasz Drwiega <tomasz@parity.io>

* Use `find_pre_digest` after runtime, too

Also, use `Member` trait rather than rolling our own requirements.

Suggested-by: Tomasz Drwiega <tomasz@parity.io>

* Fix various warnings

mostly due to upgrading the dependency on `error_chain`.

* Pre-digests nearly complete

This nearly completes the implementation of pre-runtime digests.

* `Seal2` → `Seal` and fix test suite

* Try to fix the storage error

* Try to fix storage (again)

* Fix tests

* Hopefully finish pre-runtime digests

The key is to pass *only* the pre-runtime digests to the runtime.  The
others must be stripped out by `initialize_block`.

* Fix silly typo

* Fix another silly mistake

* Remove unnecessary filtering of BABE pre-digests

We no longer get duplicate BABE pre-digests, so if they appear, the
header should be rejected outright.

* Update Cargo.lock files

* Reformatting

* Fix silly typo in inherent digest code

Also, revert `error.rs` files that contained calls to the `error_chain!`
macro.

* Try to keep the runtime from stripping pre-digests

Currently runs into the “Storage root must match that calculated”
assertion.

* Don’t compute storage root until storage changes are done.

Also, fix a compilation error.

* Fix compile-time error

* Fix compilation errors

* Fix more compile errors

* Hopefully it compiles this time…

* Fix compilation and add docs

* Prevent BABE from adding duplicate pre-runtime digests

Found by comparing with the AuRa code.  I also did some refactoring.

* Respond to review and fix some warnings

* Delete some dead code introduced earlier

* More dead code goes away

* `ref mut` → `&mut`

* Respond to review and fix some warnings

* Fix compilation error

* Remove unneeded `HashT` type parameter

Suggested-by: Robert Habermeier <robert@parity.io>

* Remove spurious #[allow(deprecated)]

* Document inherent digest parameter to `build_block`

* Delete `Simple` trait

It wasn’t needed

* delete wrongly added files

* Fix trait bounds

* Digest serialization tests

I also did some reformatting and cleanup.

* Apply suggestions from code review

Reformatting

Co-Authored-By: André Silva <andre.beat@gmail.com>

* Swap two arguments to `propose` and `propose_with`

Also, remove some needless unsafe code.

* Remove bogus `#![allow(deprecated)]` annotations

With the removal of the deprecated `Seal` variant, these are not needed.

* Add a missing `#[allow(deprecated)]` in the AuRa tests

* Fix silly compile error

* Fix silly compiler error

RLS did not tell me that I hadn’t fixed `babe/lib.rs`, so I missed it.

* Fixes made automatically by Cargo

substrate/core/sr-primitives/src/generic/header.rs

@@ -18,9 +18,12 @@
 
 #[cfg(feature = "std")]
 use serde::Serialize;
+#[cfg(feature = "std")]
+use log::debug;
 use crate::codec::{Decode, Encode, Codec, Input, Output, HasCompact, EncodeAsRef};
 use crate::traits::{self, Member, SimpleArithmetic, SimpleBitOps, MaybeDisplay,
-	Hash as HashT, DigestItem as DigestItemT, MaybeSerializeDebug, MaybeSerializeDebugButNotDeserialize};
+	Hash as HashT, DigestItem as DigestItemT, MaybeSerializeDebug,
+	MaybeSerializeDebugButNotDeserialize};
 use crate::generic::Digest;
 
 /// Abstraction over a block header for a substrate chain.
@@ -107,22 +110,29 @@ impl<Number, Hash, DigestItem> traits::Header for Header<Number, Hash, DigestIte
 	fn set_parent_hash(&mut self, hash: Self::Hash) { self.parent_hash = hash }
 
 	fn digest(&self) -> &Self::Digest { &self.digest }
+
+	#[cfg(feature = "std")]
+	fn digest_mut(&mut self) -> &mut Self::Digest {
+		debug!(target: "header", "Retrieving mutable reference to digest");
+		&mut self.digest
+	}
+
+	#[cfg(not(feature = "std"))]
 	fn digest_mut(&mut self) -> &mut Self::Digest { &mut self.digest }
-	fn set_digest(&mut self, digest: Self::Digest) { self.digest = digest }
 
 	fn new(
 		number: Self::Number,
 		extrinsics_root: Self::Hash,
 		state_root: Self::Hash,
 		parent_hash: Self::Hash,
-		digest: Self::Digest
+		digest: Self::Digest,
 	) -> Self {
 		Header {
 			number,
 			extrinsics_root,
 			state_root,
 			parent_hash,
-			digest
+			digest,
 		}
 	}
 }