[BUG] Assertion of Validity causes crash.

[SamHSmith]

After responding to a ProcessSyncedValue message with a proposal marked valid we get this crash. (Sometimes.)

The application panicked (crashed).
Message:  assertion left == right failed
  left: Invalid
 right: Valid
Location: /home/sam/.cargo/git/checkouts/malachite-ea1aa1be87e998cc/8a64f82/code/crates/core-consensus/src/handle/decide.rs:64

[cason]

Can you please detail you setup? What is the ValuePayload mode?

From a generic overview, you have a full_proposal reported as invalid that was decided. This probably happens because the full proposal was previously received by the node and the application reported it as invalid. Now, since a certificate for it was received from ValueSync, it became decide, despite being invalid.

It is expected the process to panic in this case, but I am curious to understand the scenario better.

[SamHSmith]

So it is not possible for values to change from being invalid to valid?

[cason]

So it is not possible for values to change from being invalid to valid?

Good point, it should be (as for https://github.com/circlefin/malachite/blob/main/specs/consensus/overview.md#validation)! But I am not sure if the software actually supports this, apparently it does not.

[cason]

But in any case, your application should tell consensus that v was invalid, then that v has became valid. Not sure how this can be done, this "change of mind" is supposed to happen after a node restart.

[cason]

Indeed, we ignore a Input::Proposal(p, true) if a Input::Proposal(p, false) was already stored:

malachite/code/crates/core-driver/src/proposal_keeper.rs

Lines 70 to 78 in 76d25e5

	pub fn add(
	&mut self,
	proposal: SignedProposal<Ctx>,
	validity: Validity,
	) -> Result<(), RecordProposalError<Ctx>> {
	// Ignore exact duplicates
	if self.proposals.iter().any(|(p, _)| p == &proposal) {
	return Ok(());
	}