IDerivationState.POSSIBLY_STALE + observableRequiresReaction = warning

[Bnaya]

I don't have a minimal repro or test case yet

Minimal repro:

    test("don't warn on reads inside a computed, when reaction updates the observed value", function () {
        try {
            // #916
            mobx.configure({ observableRequiresReaction: true })
            const a = mobx.observable.box(0)
            const b = mobx.observable.box(0)
            const c = mobx.computed(() => a.get() + b.get())
            const values = []

            mobx.autorun(() => {
                values.push(c.get())
                b.set(100)
            })

            const messages = utils.supressConsole(() => {
                a.set(1)
            })

            console.log(messages)

// [warn] [mobx] Observable ComputedValue@4 being read outside a reactive context
            expect(messages.length).toBe(0)
        } finally {
            mobx.configure({ observableRequiresReaction: false })
        }
    })

The observableRequiresReaction is triggered when hitting the following code path:
https://github.com/mobxjs/mobx/blob/master/src/core/derivation.ts#L93-L109

        case IDerivationState.POSSIBLY_STALE: {
            const prevUntracked = untrackedStart() // no need for those computeds to be reported, they will be picked up in trackDerivedFunction.

Due to the untrackedStart call

Related #916

Possible fix:
Make untrackedStart/untrackedEnd to have own globalState flag?

[urugator]

Weird ... IIRC untracked shouldn't have any effect on allowStateReads which is the relevant flag for raising the error (rather than actual presence of derivation - that was the point of the rewrite...)

[Bnaya]

Maybe it's something else
I will look again

[urugator]

It's not because of untracked.
What happens is, that you modify the observable, which notifies the computed, which has to recompute, which accesses the observable - at this point allowStateReads is false.
autorun is or isn't invoked later based on the computation result.
We have to allowStateReads during the recomputation.

[Bnaya]

PR up

[Bnaya]

published

[lock]

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