JSONPatch Formatter Results Are Invalid With Multiple Moves

[mgreystone]

When performing multiple move operations, the results from the jsonpatch formatter are not correct. Applying them does not results in the desired object.

Here is an example reversing the items in an array.

import { create } from 'jsondiffpatch'
import { format } from 'jsondiffpatch/formatters/jsonpatch'
import jsonpatch from 'jsonpatch'

const jsondiffpatch = create({
  arrays: {
    detectMove: true,
  },
});

const a = ["first", "second", "third", "fourth", "fifth"];
const b = ["fifth", "fourth", "third", "second", "first"];

const diff = jsondiffpatch.diff(a, b);
/*
diff is {
  _t: 'a',
  _1: [ '', 3, 3 ],
  _2: [ '', 2, 3 ],
  _3: [ '', 1, 3 ],
  _4: [ '', 0, 3 ]
}
*/

const patchedwithdiff = jsondiffpatch.patch(a, diff)
/*
This is correct:
patchedwithdiff is [ 'fifth', 'fourth', 'third', 'second', 'first' ]
*/

const patch = format(diff, a)
/*
This is not correct:
patch is: [
  { op: 'move', from: '/1', path: '/3' },
  { op: 'move', from: '/2', path: '/2' },
  { op: 'move', from: '/3', path: '/1' },
  { op: 'move', from: '/4', path: '/0' }
]
---
There are many ways to get the desired results,
but one way looks like this: [
  { op: 'move', from: '/0', path: '/4' },
  { op: 'move', from: '/0', path: '/4' },
  { op: 'move', from: '/0', path: '/4' },
  { op: 'move', from: '/0', path: '/4' },
  { op: 'move', from: '/0', path: '/4' },
]
*/

const patchedwithjson = jsonpatch.apply_patch(a, patch)
/*
patchedwithjson is: [ 'first', 'fifth', 'fourth', 'third', 'second' ]
we expected: ["fifth", "fourth", "third", "second", "first"]
*/

[atsjo]

Seeing this bug report made me disable detecting moves, so thanx for the bug report! From what I understand looking at the delta format moves in the source code (how it implements delta moves), it seems to run the move as a delete for all patches in the array first, and then do the inserts after... The logic formatting json-patch moves doesn't handle it this way, it just transforms the delta moves 1-1, and that doesn't work with the json-patch moves, where delete and insert per move is done immediately

[benjamine]

fixed in 0.7.2, thanks a lot for the detailed report!
this was a bit tricky to get right :)