Context returned in `onMutate` is not available in `onError` hook (and `onMutate` has no errors)

[ymansurozer]

I am implementing a basic optimistic to-do inspired by @posva's PR on Atidone. But I have an issue where the context I return in onMutate is not being available in onError. And I am certain onMutate is not erroring.

Reproduction: https://github.com/ymansurozer/optimistic/blob/main/pages/basic.vue

Reproduction code (quite simple so I am adding it here too):

const { mutate } = useMutation({
  mutation: (data: Omit<Todo, 'id'>) => $fetch('/api/non-existent', { method: 'POST', body: { todo: data } }),

  onMutate: () => {
    try {
      const context = { test: 'data' }
      console.log('>> Context from onMutate', context)
      return context
    }
    catch (error) {
      console.error('>> Error in onMutate', error)
      return { test: 'data' }
    }
  },

  onError: (error, variables, { test }) => {
    console.log('>> Context from onError', test)
    console.log('>> Variables', variables)
  },
})

And the logs:

>> Context from onMutate {test: 'data'}        
404 (Page not found: /api/non-existent)
>> Context from onError undefined
>> Variables Proxy(Object) {text: 'test', completed: false}

P.S.: I am working on a generic useOptimisticList composable to simplify optimistic updates for all CRUD operations for a basic list. The composable is here and a sample usage is here. basic.vue is a stripped version to show the bug. I was hoping we could include the composable in the cookbooks in the docs, if you're open to it @posva. Happy to create a PR. ❤️

[posva]

Thanks! I fixed the bug locally, I will push it and release later, there are a few changes coming up

[posva]

Regarding the optimistic updates: of course we can add a cookbook entry in the future. I was planning on releasing a plugin to handle optimistic updates for classic scenarios (list + detail calls). The plugin API is still experimental but I would love to have feedback around it! But maybe a composable is indeed an easier choice

[ymansurozer]

Thank you Eduardo!

To be perfectly honest with you, I haven't looked at the plugin API so haven't thought about it. But I'll do so because it does look promising.