From 8de29f0ee94f7652434a8c1e9c3f432be4137d65 Mon Sep 17 00:00:00 2001
From: Corbin Crutchley <git@crutchcorn.dev>
Date: Fri, 20 Dec 2024 11:43:23 -0800
Subject: [PATCH] fix: dispatches in watchEffect should no longer trigger when
 selector is changed

---
 examples/vue/simple/src/App.vue               |  5 +++
 .../src/compositions/use-selector.ts          | 17 +++----
 ...ackless-shallow-ref-with-equality-check.ts | 44 +++++++++++++++++++
 3 files changed, 58 insertions(+), 8 deletions(-)
 create mode 100644 packages/vue-redux/src/utils/use-trackless-shallow-ref-with-equality-check.ts

diff --git a/examples/vue/simple/src/App.vue b/examples/vue/simple/src/App.vue
index 486be4e..34973b7 100644
--- a/examples/vue/simple/src/App.vue
+++ b/examples/vue/simple/src/App.vue
@@ -2,9 +2,14 @@
 import { useSelector, useDispatch } from '@reduxjs/vue-redux'
 import { decrement, increment } from './store/counter-slice'
 import { RootState } from './store'
+import { watchEffect } from 'vue'
 
 const count = useSelector((state: RootState) => state.counter.value)
 const dispatch = useDispatch()
+
+watchEffect(() => {
+  dispatch(increment())
+})
 </script>
 
 <template>
diff --git a/packages/vue-redux/src/compositions/use-selector.ts b/packages/vue-redux/src/compositions/use-selector.ts
index cf2975c..205dd9a 100644
--- a/packages/vue-redux/src/compositions/use-selector.ts
+++ b/packages/vue-redux/src/compositions/use-selector.ts
@@ -1,5 +1,6 @@
-import { shallowReadonly, shallowRef, toRaw, watch } from 'vue'
+import { shallowReadonly, watch } from 'vue'
 import { ContextKey } from '../provider/context'
+import { useTracklessShallowRefWithEqualityCheck } from '../utils/use-trackless-shallow-ref-with-equality-check'
 import {
   createReduxContextComposition,
   useReduxContext as useDefaultReduxContext,
@@ -93,18 +94,17 @@ export function createSelectorComposition(
 
     // TODO: Introduce wrappedSelector for debuggability
 
-    const selectedState = shallowRef(selector(store.getState() as TState))
+    const selectedState = useTracklessShallowRefWithEqualityCheck(
+      selector(store.getState() as TState),
+      equalityFn,
+    )
 
     watch(
       () => store,
       (_, __, onCleanup) => {
         const unsubscribe = subscription.addNestedSub(() => {
           const data = selector(store.getState() as TState)
-          if (equalityFn(toRaw(selectedState.value) as Selected, data)) {
-            return
-          }
-
-          selectedState.value = data
+          selectedState.ref.value = data
         })
 
         onCleanup(() => {
@@ -113,10 +113,11 @@ export function createSelectorComposition(
       },
       {
         immediate: true,
+        deep: false,
       },
     )
 
-    return shallowReadonly(selectedState)
+    return shallowReadonly(selectedState.ref)
   }
 
   Object.assign(useSelector, {
diff --git a/packages/vue-redux/src/utils/use-trackless-shallow-ref-with-equality-check.ts b/packages/vue-redux/src/utils/use-trackless-shallow-ref-with-equality-check.ts
new file mode 100644
index 0000000..5f71ac9
--- /dev/null
+++ b/packages/vue-redux/src/utils/use-trackless-shallow-ref-with-equality-check.ts
@@ -0,0 +1,44 @@
+import { customRef } from 'vue'
+import type { Ref } from 'vue'
+import type { EqualityFn } from '../types'
+
+/**
+ * In some instances, `watch` will attempt to read the value from an inner ref,
+ * even when not part of the `() => ...` function. This can cause unwanted
+ * side effects to occur.
+ *
+ * To sidestep this, we can expose the inner value as an untracked property
+ */
+export function useTracklessShallowRefWithEqualityCheck<T>(
+  initialValue: T,
+  equalityFn: EqualityFn<T>,
+): {
+  untrackedValue: { get(): T; set(_newValue: T): void }
+  ref: Ref<T>
+} {
+  let untrackedValue = initialValue
+  return {
+    // Avoid stale values by exposing the inner value as an untracked property
+    untrackedValue: {
+      get() {
+        return untrackedValue
+      },
+      set(_newValue: T) {},
+    },
+    ref: customRef((track, trigger) => {
+      return {
+        get() {
+          track()
+          return untrackedValue
+        },
+        set(newValue: T) {
+          if (equalityFn(untrackedValue, newValue)) {
+            return
+          }
+          untrackedValue = newValue
+          trigger()
+        },
+      }
+    }),
+  }
+}