Recursive type maximum call stack exceeded

[Amareis]

This code (in pure mst) works well:

const LateMessage = types.late((): IAnyModelType => Message)

export const Message = types.model('Message', {
    id: types.identifier,
    quoted: types.maybeNull(LateMessage),
})

But this code is failing (when creating from snapshot):

const LateMessage = types.late((): IAnyModelType => Message)

const MessageData = types.model('MessageData', {
    id: types.identifier,
    quoted: types.maybeNull(LateMessage),
})

class MessageCode extends shim(MessageData) {
}

export const Message = mst(MessageCode, MessageData, 'Message')

[Amareis]

@jjrv can you fix it or explain how it can be fixed in classy-mst, please?

[jjrv]

It looks like a recursive type: Message contains a field quoted containing another Message and as far as the types are concerned the nesting could be infinite, even if in practice you only nest once. The section Recursive types details how to get that working.

[Amareis]

But with types.late typescript don't complain about circular type. There is only runtime error because of incorrect handling of maybeNull, I think.

[jjrv]

I found that a slightly improved fix to #8 also would fix this, however while disabling polymorphism support for the Message type (so you cannot then inherit from it, serialize to a snapshot and correctly deserialize different types of messages).

The diff of classy-mst.ts is:

-       let Model = Data.preProcessSnapshot(
-               // Instantiating a union of models requires a snapshot.
-               (snap: any) => snap || {}
-       ).postProcessSnapshot((snap: any) => {
+       let Model = Data.postProcessSnapshot((snap: any) => {

-       return(polymorphic(Code, Model, modelName));
+       return(Model as any);

Can you test it? I'll need to add a new options object to allow toggling this fix on/off.

[jjrv]

Actually it seems a mobx-state-tree bug has been fixed and that preProcessSnapshot hook is no longer needed. Meanwhile it actually triggers this bug... For some reason simply removing the hook fixes this, and as you see the hook does nothing but ensures there is a snapshot, because without one creating union instances used to fail.

[Amareis]

Sooo, what is the final fix? Just remove preProcessSnapshot form classy-mst.ts?

[jjrv]

Try and see if it works for you. Seems to still cause some tests to fail. I'll fix this one way or another and release a new version. Disabling polymorphism for the type may still be necessary.

[Amareis]

Ok, i'll try it.

[Amareis]

Yeah, removing of preProcessSnapshot did the trick!

Anyway, I already refactor my Message type to use types.reference to quoted, so it working without fix, but thank you for help, I'll wait for the release.

[jjrv]

OK, version 3.5.0 is out. It now works with a flag:

export const Message = mst(MessageCode, MessageData, 'Message', { sealed: true })

[jjrv]

Thanks for reporting!