This fully removes BIP9 support.
- There are no plans to use BIP9 to decide anything.
- BIP9 is designed specifically for one-way binary consensus changes;
being a minority chain, BIP9 will be difficult to use for the forseeable future.[BIP9 may be useful for timing activation of non-controversial features even on a minority chain.]
- BIP9 is fundamentally incompatible with Bitcoin Cash periodic network upgrades (regardless of our opinions about the ideal frequency).
- BIP9 does not take the per-block Difficulty Adjustment Algorithm of Bitcoin Cash into account (some blocks represent more hash than others).
- A significant part of BIP9 and perhaps the most useful part (getblocktemplate) is missing from the implementation. (!72 (merged))
- There are no plans to maintain this code, causing it to rot.
- If in the future we do decide to use miner voting for whatever reason, BIP9 is not at all guaranteed to be the best choice for that situation - we should carefully reevaluate how we want the voting system to work, and not just pick BIP9 because we-need-something-this-is-something.
Cleanly removing BIP9 now makes it easier to implement future voting systems without interfering with legacy BIP9 code.[The current BIP9 code may actually be a good start for such future implementations.]
Summary of source code changes
- consensus/params.h: BIP9-related structures removed.
- consensus/params.h, chainparams.cpp: BIP9-related chain parameter fields removed.
- rpc/blockchain.cpp: getblockchaininfo now simply sets the softforks field to an empty object (for backward compatibility)
- validation.h, validation.cpp: BIP9-related functions removed.
- validation.cpp: ComputeBlockVersion now simply returns VERSIONBITS_TOP_BITS.
- versionbits.h, versionbits.cpp: only version constants left behind.
- versionbitsinfo.h, versionbitsinfo.cpp: removed.
Unit test versionbits_tests is removed.
Functional test rpc_blockchain is changed to no longer expect to see the testdummy soft fork.
How code changes were located
I manually reviewed the following Bitcoin ABC differentials to locate all code to remove:
- D5282 Implement miner funding features
- D5218 Update blockchain RPC to report all BIP9 based on versionbitsinfo
- D5139 Ensure the thresold for BIP9 can be configured on a per activation basis.
- D5135 Restore BIP9 RPC support in getblockchaininfo
- D5134 Ressurect BIP9 style activation mechanism
In combination with further searches, making the thing compile, and making tests succeed, I am sufficiently confident all BIP9 code is removed.
Test as follows: (both build paths - ninja & autoconf)
- build (
ninja && ninja test_bitcoinfor ninja build)
- run unit tests:
- full regression tests: