Merge pull request #376 from margelo/osp/fix-concurrency-with-set-state

Fix race condition when tempState is deleted before loading flag is set to false

lib/withOnyx.js

@@ -146,7 +146,13 @@ export default function (mapOnyxToState, shouldDelayUpdates = false) {
                 const prevValue = this.state[statePropertyName];
 
                 // If the component is not loading (read "mounting"), then we can just update the state
-                if (!this.state.loading) {
+                // There is a small race condition.
+                // When calling setWithOnyxState we delete the tempState object that is used to hold temporary state updates while the HOC is gathering data.
+                // However the loading flag is only set on the setState callback down below. setState however is an async operation that is also batched,
+                // therefore there is a small window of time where the loading flag is not false but the tempState is already gone
+                // (while the update is queued and waiting to be applied).
+                // This simply bypasses the loading check if the tempState is gone and the update can be safely queued with a normal setStateProxy.
+                if (!this.state.loading || !this.tempState) {
                     // Performance optimization, do not trigger update with same values
                     if (prevValue === val || utils.areObjectsEmpty(prevValue, val)) {
                         return;