items dissappear from sequence when moved

[nrw]

I'm picking on crdt, but the problem could be in level-scuttlebutt or level-js. I made an example here https://github.com/nrw/seq-example.

summary: open doc. fill sequence. move items around in the sequence. close doc. reopen. any moved item is missing from the sequence.

Is my usage wrong or is something broken?

[nrw]

Update: the problem persists when level-js is omitted from the example.

[dominictarr]

a manual test is not good, if you have found a bug you need to make an automatic test. can you make this test do the wait and then check thing automatically?

this may be a sync race condition, the after overwrites the push({id: 'a'})... it probably works if you do this asynchronously (because no one has complained about this before), but this should work, thierefore what is needed is a testcase.

[nrw]

I'll try to find a way to make this test automatic.

[nrw]

I just pushed an automatic test case: https://github.com/nrw/seq-example

assertion should pass. it fails.

[dominictarr]

Hmm, can you make this work just in one process without using child_process? then it will be easyiest to debug.

[nrw]

This is my attempt. In this one, the sequences still don't match, but they don't match in a different way. https://github.com/nrw/seq-example/blob/master/single-process.js

The first sequence is as expected. the second is totally empty.

[nrw]

I just pushed an update. This test case now reproduces the original symptoms in a single process: https://github.com/nrw/seq-example/blob/master/single-process.js

[dominictarr]

okay, digging into this - it's probably actually a level-scuttlebutt issue... maybe because of nextTicks. I've upated level-scuttlebutt to test with the latest deps, and it's failing one test. this may be related...

[nrw]

i thought it might be a level-scuttlebutt issue. thanks for digging in!

[dominictarr]

Aha... I have found the problem!

It is about the way that crdt tries to cleanup old updates - it creates one update that adds a into the sequence - and then the next update moves it after b, yet it was deleting the first update.

by filtering the deletes out I got it to work - but the solution is getting crdt to emit the correct _remove events

[dominictarr]

This is fixed in 3.6.2! also, you should upgrade to level-scuttlebutt@5.0.8 which has your script added as a test. (with the small change to use toJSON instead of asArray)

[nrw]

Hooray! Thanks!