Refactor TrieValidatorSet to close issue #1186

[jskskjnekd]

Original Problem #1186

Optimize TrieValidatorSet.

Currently, the two main sources are

trie -> [validatorIndex: Validator] index -> a key-value source [pubKey: validatorIndex]

Proposal of #1186

trie -> [blake2b(pubKey): validator] index -> a key-value source [validatorIndex: pubKey]

Main problem of this proposal is that, after the refactoring, when we use the function getSnapshotTo, the validator could not be found from source index.

The main reason is that, trie got updated through getSnapshotTo but not the source of index. We can conclude that, validatorIndex is the data source we should also keep update. It means that, if we need to get access to validators through indices, the indices are always updated and correct.

New Proposal

As a result, I propose to make a small modification on two sources.

trie -> [validatorIndex: pubKey] index -> [blake2b(pubKey): validator]

• Two main sources can pass all the test on TrieValidatorSetTest.java, including the testSnapshotTo.
• validatorIndex is always updated; signature aggregation checks where validators are gonna be accessed by their indices can be processed correctly;
• All the validators can be accessed by pubKey.

[mkalinin]

We are not maintaining this implementation anymore. Sorry about that. Let me close all related issues to avoid any further confusion.