Make patricia-trie usable from Polkadot (WAS: Extract patricia-trie to its own repo)

[rphmeier]

Along with various bits of generalization in it and its dependencies to make generic over hash function, hash type, and node encoding and decoding.

CC paritytech/polkadot#157

[dvdplm]

Tasks:

• make trait Hash generic over the hashing algorithm (investigate doing this in the hashdb crate, see Modifications for better cross-project use of HashDB/Patricia Trie #7019)
• make Node generic over hash; add a NodeCodec trait
• implement NodeCodec for rlp
• make sure encoding does not suffer performance hit; investigate using smallvec here
• port structures like TrieDB to be generic TrieDB<H: Hash, C: NodeCodec<H>>

@rphmeier looks about right to you? I'd like to do the extractions asap to avoid merge conflicts down the line as people might be making changes to the in-tree versions of the crates.

[rphmeier]

Looks about right. We might want to introduce a small crate just for the hash trait so other code (hashdb, triehash, etc.) can depend on it, and a separate crate for rlp-node-codec.

[debris]

Sorry for not replying immediately to this thread. I don't agree with one of the points here, which is extract patricia_trie's in-tree dependencies into own repos. I believe it's redundant and will introduce a lot of maintenance burden.

extract trie-standardmap – @debris this code does not have a license; you ok with GPL v3?

great catch, sure!

extract plain_hasher – @debris this crate is owned by you so I can't push updates. Can you transfer it to parity?

historically, plain_hasher was a separate repo, but it's usecase is very specific for us, and after discussing it with Arkadiy, I decided to move it to parity to avoid maintenance burden.

[5chdn]

I have no strong opinion here, but I want to highlight that we should rename ethcore-* crates to parity-* soon. If we touch this code now, let's keep it in mind. cc #8649

[adria0]

Closing the issue due to its stale state