The Consensus Cleanup soft fork proposal includes enforcing that coinbase transactions set their
locktime field to the block height, minus 1 (as well as their nSequence such as to not disable the
timelock). If such a fork were to be activated by Bitcoin users, miners need to be ready to produce
compliant blocks at the risk of losing substantial amounts mining would-be invalid blocks. As miners
are unfamously slow to upgrade, it's good to make this change as early as possible.
Although Bitcoin Core's GBT implementation does not provide the "coinbasetxn" field, and mining
pool software crafts the coinbase on its own, updating the Bitcoin Core mining code is a first step
toward convincing pools to update their (often closed source) code. A possible followup is also to
introduce new fields to GBT. In addition, this first step also makes it possible to test future
Consensus Cleanup changes.
The changes to the seemingly-unrelated RBF tests is because these tests assert an error message
which may vary depending on the txid of the transactions used in the test. This commit changes the
coinbase transaction structure and therefore impact the txid of transactions in all tests.
The change to the "Bad snapshot" error message in the assumeutxo functional test is because this
specific test case reads into the txid of the next transaction in the snapshot and asserts the error
message based it gets on deserializing this txid as a coin for the previous transaction. As this
commit changes this txid it impacts the deserialization error raised.
Recently added mempool_util implementation probably evolved in parallel with the package RBF one before being submitted as part of ephemeral dust in e2e30e89ba4b9bdbcabaf5b4346610922f0728bb.
