fix: proof-of-concept to support virtual fields added by hooks in buildFormState

[brumm]

How come?

I am building a setup where a base collection Persons is referenced by other collections like Employees and Users. To make editing that base data seamless, I include fields from Persons in a virtual group on other collections, in this example Employees like so:

Config

const embeddedPersonField: Field = {
  name: 'personalData',
  type: 'group',
  virtual: true,
  fields: Persons.fields,
}

export const Employees: CollectionConfig = {
  slug: 'employees',
  hooks: {
    afterRead: [populateEmbeddedPersonData],
    beforeChange: [saveEmbeddedPersonData],
  },
  fields: [
    {
      name: 'persons',
      type: 'relationship',
      relationTo: 'persons',
    },
    embeddedPersonField,
  ],
}

The data is populated and saved by hooks.

The bug: selecting a Person from the relationship dropdown re-renders the form after a request to form-state, but does not include field values from the selected Person.

See a gif

What?

Run afterRead hooks in buildFormState and accept server-computed values in the onChange form state merge.

Why?

Virtual fields populated by afterRead hooks return empty when a relationship field changes in the admin panel. Two things prevent this:

• buildFormState never runs afterRead hooks. On initial load, Document/index.tsx fetches via payload.findByID() (which runs hooks) and passes the result to buildFormState. On subsequent rebuilds triggered by field changes, hooks are skipped entirely.

• mergeServerFormState discards the server-computed values. The onChange codepath dispatches MERGE_SERVER_STATE without acceptValues, so shouldAcceptValue is false and value/initialValue are stripped.

How?

• Export afterRead from payload core
• Call field-level and collection/global-level afterRead hooks in buildFormState (guarded by isTopLevelSchema)
• Pass acceptValues: { overrideLocalChanges: false } in the onChange merge so server-computed values are accepted for unmodified fields

Note on architecture

• We just run that one hook here as a proof-of-concept.
• This imports afterRead directly from payload core into @payloadcms/ui. As far as I can tell, no other UI code currently does this. An alternative could be to expose something like payload.runAfterReadHooks(collection, doc) on the Payload instance.