Better React 18 support

.changeset/early-terms-bow.md

@@ -0,0 +1,7 @@
+---
+"mobx-react": minor
+"mobx-react-lite": minor
+"mobx": patch
+---
+
+TODO

.vscode/settings.json

@@ -1,9 +1,11 @@
 {
     "[typescript]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode",
         "editor.formatOnSave": true,
         "editor.formatOnPaste": false
     },
     "[javascript]": {
+        "editor.defaultFormatter": "esbenp.prettier-vscode",
         "editor.formatOnSave": true,
         "editor.formatOnPaste": false
     },

packages/mobx-react-lite/__tests__/strictAndConcurrentModeUsingFinalizationRegistry.test.tsx

@@ -1,21 +1,20 @@
 import { cleanup, render } from "@testing-library/react"
 import * as mobx from "mobx"
 import * as React from "react"
-
 import { useObserver } from "../src/useObserver"
 import { sleep } from "./utils"
-import { FinalizationRegistry } from "../src/utils/FinalizationRegistryWrapper"
-
-// @ts-ignore
 import gc from "expose-gc/function"
+import { observerFinalizationRegistry } from "../src/utils/observerFinalizationRegistry"
+
+if (typeof globalThis.FinalizationRegistry !== "function") {
+    throw new Error("This test must run with node >= 14")
+}
+
+expect(observerFinalizationRegistry).toBeInstanceOf(globalThis.FinalizationRegistry)
 
 afterEach(cleanup)
 
 test("uncommitted components should not leak observations", async () => {
-    if (!FinalizationRegistry) {
-        throw new Error("This test must run with node >= 14")
-    }
-
     const store = mobx.observable({ count1: 0, count2: 0 })
 
     // Track whether counts are observed

packages/mobx-react-lite/__tests__/strictAndConcurrentModeUsingTimers.test.tsx

@@ -2,21 +2,22 @@ import "./utils/killFinalizationRegistry"
 import { act, cleanup, render } from "@testing-library/react"
 import * as mobx from "mobx"
 import * as React from "react"
-
 import { useObserver } from "../src/useObserver"
 import {
-    forceCleanupTimerToRunNowForTests,
-    resetCleanupScheduleForTests
-} from "../src/utils/reactionCleanupTracking"
-import {
-    CLEANUP_LEAKED_REACTIONS_AFTER_MILLIS,
-    CLEANUP_TIMER_LOOP_MILLIS
-} from "../src/utils/reactionCleanupTrackingCommon"
+    REGISTRY_FINALIZE_AFTER,
+    REGISTRY_SWEEP_INTERVAL
+} from "../src/utils/UniversalFinalizationRegistry"
+import { observerFinalizationRegistry } from "../src/utils/observerFinalizationRegistry"
+import { TimerBasedFinalizationRegistry } from "../src/utils/UniversalFinalizationRegistry"
+
+expect(observerFinalizationRegistry).toBeInstanceOf(TimerBasedFinalizationRegistry)
+
+const registry = observerFinalizationRegistry as TimerBasedFinalizationRegistry<unknown>
 
 afterEach(cleanup)
 
 test("uncommitted components should not leak observations", async () => {
-    resetCleanupScheduleForTests()
+    registry.finalizeAllImmediately()
 
     // Unfortunately, Jest fake timers don't mock out Date.now, so we fake
     // that out in parallel to Jest useFakeTimers
@@ -51,7 +52,7 @@ test("uncommitted components should not leak observations", async () => {
     )
 
     // Allow any reaction-disposal cleanup timers to run
-    const skip = Math.max(CLEANUP_LEAKED_REACTIONS_AFTER_MILLIS, CLEANUP_TIMER_LOOP_MILLIS)
+    const skip = Math.max(REGISTRY_FINALIZE_AFTER, REGISTRY_SWEEP_INTERVAL)
     fakeNow += skip
     jest.advanceTimersByTime(skip)
 
@@ -72,7 +73,7 @@ test("cleanup timer should not clean up recently-pended reactions", () => {
     // 5. The commit phase runs for component A, but reaction R2 has already been disposed. Game over.
 
     // This unit test attempts to replicate that scenario:
-    resetCleanupScheduleForTests()
+    registry.finalizeAllImmediately()
 
     // Unfortunately, Jest fake timers don't mock out Date.now, so we fake
     // that out in parallel to Jest useFakeTimers
@@ -106,7 +107,7 @@ test("cleanup timer should not clean up recently-pended reactions", () => {
     // We force our cleanup loop to run even though enough time hasn't _really_
     // elapsed.  In theory, it won't do anything because not enough time has
     // elapsed since the reactions were queued, and so they won't be disposed.
-    forceCleanupTimerToRunNowForTests()
+    registry.sweep()
 
     // Advance time enough to allow any timer-queued effects to run
     jest.advanceTimersByTime(500)
@@ -137,7 +138,7 @@ test.skip("component should recreate reaction if necessary", () => {
 
     // This unit test attempts to replicate that scenario:
 
-    resetCleanupScheduleForTests()
+    registry.finalizeAllImmediately()
 
     // Unfortunately, Jest fake timers don't mock out Date.now, so we fake
     // that out in parallel to Jest useFakeTimers
@@ -166,9 +167,9 @@ test.skip("component should recreate reaction if necessary", () => {
     // and _then_ the component commits.
 
     // Force everything to be disposed.
-    const skip = Math.max(CLEANUP_LEAKED_REACTIONS_AFTER_MILLIS, CLEANUP_TIMER_LOOP_MILLIS)
+    const skip = Math.max(REGISTRY_FINALIZE_AFTER, REGISTRY_SWEEP_INTERVAL)
     fakeNow += skip
-    forceCleanupTimerToRunNowForTests()
+    registry.sweep()
 
     // The reaction should have been cleaned up.
     expect(countIsObserved).toBeFalsy()

packages/mobx-react-lite/package.json

@@ -36,7 +36,9 @@
         "url": "https://github.com/mobxjs/mobx/issues"
     },
     "homepage": "https://mobx.js.org",
-    "dependencies": {},
+    "dependencies": {
+        "use-sync-external-store": "^1.2.0"
+    },
     "peerDependencies": {
         "mobx": "^6.1.0",
         "react": "^16.8.0 || ^17 || ^18"

packages/mobx-react-lite/src/index.ts

@@ -5,6 +5,7 @@ import { observerBatching } from "./utils/observerBatching"
 import { useDeprecated } from "./utils/utils"
 import { useObserver as useObserverOriginal } from "./useObserver"
 import { enableStaticRendering } from "./staticRendering"
+import { observerFinalizationRegistry } from "./utils/observerFinalizationRegistry"
 
 observerBatching(batch)
 
@@ -14,7 +15,9 @@ export { Observer } from "./ObserverComponent"
 export { useLocalObservable } from "./useLocalObservable"
 export { useLocalStore } from "./useLocalStore"
 export { useAsObservableSource } from "./useAsObservableSource"
-export { resetCleanupScheduleForTests as clearTimers } from "./utils/reactionCleanupTracking"
+
+export { observerFinalizationRegistry as _observerFinalizationRegistry }
+export const clearTimes = observerFinalizationRegistry["finalizeAllImmediately"] ?? (() => {})
 
 export function useObserver<T>(fn: () => T, baseComponentName: string = "observed"): T {
     if ("production" !== process.env.NODE_ENV) {

packages/mobx-react-lite/src/useObserver.ts

@@ -1,118 +1,111 @@
-import { Reaction } from "mobx"
+import { Reaction, _getGlobalState } from "mobx"
 import React from "react"
 import { printDebugValue } from "./utils/printDebugValue"
-import {
-    addReactionToTrack,
-    IReactionTracking,
-    recordReactionAsCommitted
-} from "./utils/reactionCleanupTracking"
 import { isUsingStaticRendering } from "./staticRendering"
-
-function observerComponentNameFor(baseComponentName: string) {
-    return `observer${baseComponentName}`
+import { observerFinalizationRegistry } from "./utils/observerFinalizationRegistry"
+import { useSyncExternalStore } from "use-sync-external-store/shim"
+
+// Do not store `admRef` (even as part of a closure!) on this object,
+// otherwise it will prevent GC and therefore reaction disposal via FinalizationRegistry.
+type ObserverAdministration = {
+    reaction: Reaction | null // also serves as disposed flag
+    forceUpdate: Function | null // also serves as mounted flag
+    // BC: we will use local state version if global isn't available.
+    // It should behave as previous implementation - tearing is still present,
+    // because there is no cross component synchronization,
+    // but we can use `useSyncExternalStore` API.
+    stateVersion: any
+    name: string
+    // These don't depend on state/props, therefore we can keep them here instead of `useCallback`
+    subscribe: Parameters<typeof React.useSyncExternalStore>[0]
+    getSnapshot: Parameters<typeof React.useSyncExternalStore>[1]
 }
 
-/**
- * We use class to make it easier to detect in heap snapshots by name
- */
-class ObjectToBeRetainedByReact {}
+const mobxGlobalState = _getGlobalState()
+
+// BC
+const globalStateVersionIsAvailable = typeof mobxGlobalState.globalVersion !== "undefined"
 
-function objectToBeRetainedByReactFactory() {
-    return new ObjectToBeRetainedByReact()
+function createReaction(adm: ObserverAdministration) {
+    adm.reaction = new Reaction(`observer${adm.name}`, () => {
+        if (!globalStateVersionIsAvailable) {
+            // BC
+            adm.stateVersion = Symbol()
+        }
+        // Force update won't be avaliable until the component "mounts".
+        // If state changes in between initial render and mount,
+        // `useSyncExternalStore` should handle that by checking the state version and issuing update.
+        adm.forceUpdate?.()
+    })
 }
 
-export function useObserver<T>(fn: () => T, baseComponentName: string = "observed"): T {
+export function useObserver<T>(render: () => T, baseComponentName: string = "observed"): T {
     if (isUsingStaticRendering()) {
-        return fn()
+        return render()
     }
 
-    const [objectRetainedByReact] = React.useState(objectToBeRetainedByReactFactory)
-    // Force update, see #2982
-    const [, setState] = React.useState()
-    const forceUpdate = () => setState([] as any)
-
-    // StrictMode/ConcurrentMode/Suspense may mean that our component is
-    // rendered and abandoned multiple times, so we need to track leaked
-    // Reactions.
-    const reactionTrackingRef = React.useRef<IReactionTracking | null>(null)
-
-    if (!reactionTrackingRef.current) {
-        // First render for this component (or first time since a previous
-        // reaction from an abandoned render was disposed).
-
-        const newReaction = new Reaction(observerComponentNameFor(baseComponentName), () => {
-            // Observable has changed, meaning we want to re-render
-            // BUT if we're a component that hasn't yet got to the useEffect()
-            // stage, we might be a component that _started_ to render, but
-            // got dropped, and we don't want to make state changes then.
-            // (It triggers warnings in StrictMode, for a start.)
-            if (trackingData.mounted) {
-                // We have reached useEffect(), so we're mounted, and can trigger an update
-                forceUpdate()
-            } else {
-                // We haven't yet reached useEffect(), so we'll need to trigger a re-render
-                // when (and if) useEffect() arrives.
-                trackingData.changedBeforeMount = true
+    const admRef = React.useRef<ObserverAdministration | null>(null)
+
+    if (!admRef.current) {
+        const adm: ObserverAdministration = {
+            reaction: null,
+            forceUpdate: null,
+            stateVersion: Symbol(),
+            name: baseComponentName,
+            subscribe(onStoreChange: () => void) {
+                // Do NOT access admRef here!
+                observerFinalizationRegistry.unregister(adm)
+                adm.forceUpdate = onStoreChange
+                if (!adm.reaction) {
+                    // We've lost our reaction and therefore all subscriptions.
+                    // We have to recreate reaction and schedule re-render to recreate subscriptions,
+                    // even if state did not change.
+                    createReaction(adm)
+                    adm.forceUpdate()
+                }
+
+                return () => {
+                    // Do NOT access admRef here!
+                    adm.forceUpdate = null
+                    adm.reaction?.dispose()
+                    adm.reaction = null
+                }
+            },
+            getSnapshot() {
+                // Do NOT access admRef here!
+                return globalStateVersionIsAvailable
+                    ? mobxGlobalState.stateVersion
+                    : adm.stateVersion
             }
-        })
+        }
+
+        createReaction(adm)
 
-        const trackingData = addReactionToTrack(
-            reactionTrackingRef,
-            newReaction,
-            objectRetainedByReact
-        )
+        admRef.current = adm
+
+        // StrictMode/ConcurrentMode/Suspense may mean that our component is
+        // rendered and abandoned multiple times, so we need to track leaked
+        // Reactions.
+        observerFinalizationRegistry.register(admRef, adm, adm)
     }
 
-    const { reaction } = reactionTrackingRef.current!
-    React.useDebugValue(reaction, printDebugValue)
-
-    React.useEffect(() => {
-        // Called on first mount only
-        recordReactionAsCommitted(reactionTrackingRef)
-
-        if (reactionTrackingRef.current) {
-            // Great. We've already got our reaction from our render;
-            // all we need to do is to record that it's now mounted,
-            // to allow future observable changes to trigger re-renders
-            reactionTrackingRef.current.mounted = true
-            // Got a change before first mount, force an update
-            if (reactionTrackingRef.current.changedBeforeMount) {
-                reactionTrackingRef.current.changedBeforeMount = false
-                forceUpdate()
-            }
-        } else {
-            // The reaction we set up in our render has been disposed.
-            // This can be due to bad timings of renderings, e.g. our
-            // component was paused for a _very_ long time, and our
-            // reaction got cleaned up
-
-            // Re-create the reaction
-            reactionTrackingRef.current = {
-                reaction: new Reaction(observerComponentNameFor(baseComponentName), () => {
-                    // We've definitely already been mounted at this point
-                    forceUpdate()
-                }),
-                mounted: true,
-                changedBeforeMount: false,
-                cleanAt: Infinity
-            }
-            forceUpdate()
-        }
+    const adm = admRef.current!
+    React.useDebugValue(adm.reaction!, printDebugValue)
 
-        return () => {
-            reactionTrackingRef.current!.reaction.dispose()
-            reactionTrackingRef.current = null
-        }
-    }, [])
+    useSyncExternalStore(
+        // Both of these must be stable, otherwise it would keep resubscribing every render.
+        adm.subscribe,
+        adm.getSnapshot
+    )
 
     // render the original component, but have the
     // reaction track the observables, so that rendering
     // can be invalidated (see above) once a dependency changes
-    let rendering!: T
+    let renderResult!: T
     let exception
-    reaction.track(() => {
+    adm.reaction!.track(() => {
         try {
-            rendering = fn()
+            renderResult = render()
         } catch (e) {
             exception = e
         }
@@ -122,5 +115,5 @@ export function useObserver<T>(fn: () => T, baseComponentName: string = "observe
         throw exception // re-throw any exceptions caught during rendering
     }
 
-    return rendering
+    return renderResult
 }