If the first change is empty, it is not encoded properly.

[ghost]

Hi there. The following code crashes on the third change with:

let d = Automerge.init();
d = Automerge.emptyChange(d);
d = Automerge.change(d, (doc) => (doc.z = 1));
d = Automerge.change(d, (doc) => (doc.z = 1000));

The full trace is:

encoding.js:153 Uncaught RangeError: value is not an integer
    at DeltaEncoder.appendInt53 (encoding.js:153)
    at DeltaEncoder.appendRawValue (encoding.js:764)
    at DeltaEncoder.flush (encoding.js:751)
    at DeltaEncoder._appendValue (encoding.js:627)
    at DeltaEncoder.appendValue (encoding.js:573)
    at DeltaEncoder.appendValue (encoding.js:945)
    at appendOperation (new.js:636)
    at appendChange (new.js:1676)
    at BackendDoc.applyChanges (new.js:1841)
    at Object.applyLocalChange (backend.js:84)

I can tell from my debugging:

• The first change contains no ops.
• In applyLocalChange, the change has no maxOp field. The change is encoded in applyLocalChange and decoded in applyChanges. After decoding, maxOp is still undefined.
• appendChange extracts the maxOp field of the change, which is undefined.
• This undefined maxOp is encoded into the maxOp column.
• For some reason the second change does not crash.
• In the third change, DeltaEncoder accesses the first maxOp value (which is undefined) to compute the difference of the current value. This crashes with the above error.

I hope these breadcrumbs are helpful.

[ept]

Thanks @jrakow for the helpful bug report! I have fixed the issue in #457. Could you give it a try please?

[ghost]

Thanks for the quick fix. It works now.

[ghost]

(Should not have closed this issue, while the PR is still open.)