[bug] Invalid patch produced from array.splice() call

[davidye]

const x: string[] = ["a"];
const [_, patches] = create(
  x,
  (draft) => {
    draft.splice(0, 1);
  },
  { enablePatches: true }
);

console.log(patches);

This produces:

[{ op: "replace", path: "length"], value: 0 }]

When it should be a "remove" operation

[davidye]

I did see that this may be intentional from: #65

But I think the generated patch should not include "length" for it to match the JSON patch spec? FWIW immer does handle this case with "remove".

[unadlib]

hi @davidye , by default, Mutative’s patch generation rules differ slightly from the JSON Patch spec. The doc: https://github.com/unadlib/mutative?tab=readme-ov-file#createstate-fn-options.

You can set arrayLengthAssignment: false to meet your requirements.

const x: string[] = ['a'];
const [_, patches] = create(
  x,
  (draft) => {
    draft.splice(0, 1);
  },
  {
    enablePatches: {
      arrayLengthAssignment: false,
    },
  }
);

console.log(patches); // [ { op: 'remove', path: [ 0 ] } ]

Here #6 is more related discussion.

[unadlib]

This would work. I suggest defaulting to 100% spec-compatible patches.

I'm afraid not, arrayLengthAssignment should be true by default, otherwise most users using patches will suffer additional performance loss.

#6 (comment)

[davidye]

Oh I see, thank you! Excellent library by the way this is exactly what I was looking for.