bug: registered field count is +1 after server side rendered redux state rehydration

This is bug report following the changes in #2470

To reproduce this bug:

• Have a server side rendered form
• Have the server side redux state serialized and sent to the client as an initial state
• Hydrate the redux state on the client
• Mount the same form

Expected behavior is a correct count of registered fields. Assuming the field is mounted once, it should be 1 - instead it’s 1 + 1 = 2.

This occurs on any environment - regardless.

Root cause of this problem is the previous assumption of the library that when a REGISTER_FIELD event is raised - it will do an “upsert” of the field to the registeredField list. Since now there is a sort of reference counting going on - this +1 the current state.

A solution, unfortunately would be to indicate the state is server generated and prevent the initial redundant increment. Otherwise, differentiation between new registrations and additional registrations.

What is not a solution:

• Ignore SSR scenarios
• Reset the entire form state on the client - Sometimes we have initial values rendered on the server or other state which could be important.

[gustavohenke]

Because this issue saw almost no activity for a few months, I’m closing it.

[tikotzky]

This issue is affecting me as well. I am able to “fix” it by modifying the reducer to skip the REGISTER_FIELD action when running on the server

    [REGISTER_FIELD](state, { payload: { name, type } }) {
+      if (!isBrowser) return state;
      const key = `registeredFields['${name}']`
      let field = getIn(state, key)
      if (field) {
        const count = getIn(field, 'count') + 1
        field = setIn(field, 'count', count)
      } else {
        field = fromJS({ name, type, count: 1 })
      }
      return setIn(state, key, field)
    },

as @yoadsn pointed out there is a precedent for libraries changing behavior when running on the server to support SSR. (you can see that glamor does something similar here)

I’d be willing to try and take this further if this is something that redux form would be willing to accept.

Either way thanks for the great lib…