A more comprehensive model for PoV-Blocks and Candidate receipts (#843)

* encode the candidate statement as only the hash

* refactor CandidateReceipt and CollationInfo

* introduce an abridged candidate receipt type

* erasure coding stores candidate receipt

* store omitted data instead and introduce AvailableData type

* refactor availability-store schema

* tweak schema and APIs a bit more

* get availability-store tests passing

* accept AbridgedCandidateReceipt in `set_heads`

* change statement type in primitives to be hash-only

* fix parachains runtime tests

* fix bad merge

* rewrite validation pipeline

* remove evaluation module

* use abridged candidate hash as canonical

* statement table uses abridged candidate receipts

* kill availability_store::Data struct

* port shared table to new validation pipelines

* extract full validation pipeline to helper

* remove old validation pipeline from collation module

* polkadot-validation compiles

* polkadot-validation tests compile

* make local collation available in validation service

* port legacy network code

* polkadot-network fully ported

* network: ensure fresh statement is propagated

* remove pov_block_hash from LocalValidationData

* remove candidate_hash field from AttestedCandidate and update runtime

* port runtimes to new ParachainHost definition

* port over polkadot-collator

* fix test compilation

* better fix

* remove unrelated validation work dispatch fix

* address grumbles

* fix equality check

polkadot/erasure-coding/src/lib.rs

@@ -27,7 +27,7 @@
 use codec::{Encode, Decode};
 use reed_solomon::galois_16::{self, ReedSolomon};
 use primitives::{Hash as H256, BlakeTwo256, HashT};
-use primitives::parachain::BlockData;
+use primitives::parachain::AvailableData;
 use sp_core::Blake2Hasher;
 use trie::{EMPTY_PREFIX, MemoryDB, Trie, TrieMut, trie_types::{TrieDBMut, TrieDB}};
 
@@ -66,6 +66,8 @@ pub enum Error {
 	BranchOutOfBounds,
 }
 
+impl std::error::Error for Error { }
+
 #[derive(Debug, PartialEq)]
 struct CodeParams {
 	data_shards: usize,
@@ -125,11 +127,11 @@ fn code_params(n_validators: usize) -> Result<CodeParams, Error> {
 /// Obtain erasure-coded chunks, one for each validator.
 ///
 /// Works only up to 65536 validators, and `n_validators` must be non-zero.
-pub fn obtain_chunks(n_validators: usize, block_data: &BlockData)
+pub fn obtain_chunks(n_validators: usize, available_data: &AvailableData)
 	-> Result<Vec<Vec<u8>>, Error>
 {
 	let params = code_params(n_validators)?;
-	let encoded = block_data.encode();
+	let encoded = available_data.encode();
 
 	if encoded.is_empty() {
 		return Err(Error::BadPayload);
@@ -151,7 +153,7 @@ pub fn obtain_chunks(n_validators: usize, block_data: &BlockData)
 ///
 /// Works only up to 65536 validators, and `n_validators` must be non-zero.
 pub fn reconstruct<'a, I: 'a>(n_validators: usize, chunks: I)
-	-> Result<BlockData, Error>
+	-> Result<AvailableData, Error>
 	where I: IntoIterator<Item=(&'a [u8], usize)>
 {
 	let params = code_params(n_validators)?;
@@ -341,6 +343,7 @@ impl<'a, I: Iterator<Item=&'a [u8]>> codec::Input for ShardInput<'a, I> {
 #[cfg(test)]
 mod tests {
 	use super::*;
+	use primitives::parachain::{BlockData, PoVBlock};
 
 	#[test]
 	fn field_order_is_right_size() {
@@ -400,11 +403,18 @@ mod tests {
 	}
 
     #[test]
-	fn round_trip_block_data() {
-		let block_data = BlockData((0..255).collect());
+	fn round_trip_works() {
+		let pov_block = PoVBlock {
+			block_data: BlockData((0..255).collect()),
+		};
+
+		let available_data = AvailableData {
+			pov_block,
+			omitted_validation: Default::default(),
+		};
 		let chunks = obtain_chunks(
 			10,
-			&block_data,
+			&available_data,
 		).unwrap();
 
 		assert_eq!(chunks.len(), 10);
@@ -420,16 +430,23 @@ mod tests {
 			].iter().cloned(),
 		).unwrap();
 
-		assert_eq!(reconstructed, block_data);
+		assert_eq!(reconstructed, available_data);
 	}
 
 	#[test]
 	fn construct_valid_branches() {
-		let block_data = BlockData(vec![2; 256]);
+		let pov_block = PoVBlock {
+			block_data: BlockData(vec![2; 256]),
+		};
+
+		let available_data = AvailableData {
+			pov_block,
+			omitted_validation: Default::default(),
+		};
 
 		let chunks = obtain_chunks(
 			10,
-			&block_data,
+			&available_data,
 		).unwrap();
 
 		assert_eq!(chunks.len(), 10);