fix(repeat): array sync issue when inserting during leave animation

src/array-repeat-strategy.js

@@ -103,6 +103,45 @@ export class ArrayRepeatStrategy {
   }
 
   _standardProcessInstanceMutated(repeat, array, splices) {
+    if (repeat.__queuedSplices) {
+      repeat.__queuedSplices.push({ repeat, array, splices });
+      return;
+    }
+
+    let maybePromise = this._runSplices(repeat, array, splices);
+    if (maybePromise instanceof Promise) {
+      let queuedSplices = repeat.__queuedSplices = [];
+
+      let runQueuedSplices = () => {
+        if (! queuedSplices.length) {
+          delete repeat.__queuedSplices;
+          return;
+        }
+
+        // TODO: coalesce/normalise queuedSplices here
+
+        // TODO: if the splices are coalesced then _runSplices only has to be
+        //       called once here, will be faster and simpler.
+        let nextSplice = queuedSplices.shift();
+        let nextPromise = this._runSplices(nextSplice.repeat, nextSplice.array, nextSplice.splices) || Promise.resolve();
+        nextPromise.then(runQueuedSplices);
+      }
+
+      maybePromise.then(runQueuedSplices);
+    }
+  }
+
+  /**
+  * Run a normalised set of splices against the viewSlot children.
+  * @param repeat The repeat instance.
+  * @param array The modified array.
+  * @param splices Records of array changes.
+  * @return {Promise|undefined} A promise if animations have to be run.
+  * @pre The splices must be normalised so as:
+  *  * Any item added may not be later removed.
+  *  * Removals are ordered by asending index
+  */
+  _runSplices(repeat, array, splices) {
     let removeDelta = 0;
     let viewSlot = repeat.viewSlot;
     let rmPromises = [];
@@ -112,6 +151,7 @@ export class ArrayRepeatStrategy {
       let removed = splice.removed;
 
       for (let j = 0, jj = removed.length; j < jj; ++j) {
+        // the rmPromises.length correction works due to the ordered removal precondition
         let viewOrPromise = viewSlot.removeAt(splice.index + removeDelta + rmPromises.length, true);
         if (viewOrPromise instanceof Promise) {
           rmPromises.push(viewOrPromise);
@@ -121,7 +161,7 @@ export class ArrayRepeatStrategy {
     }
 
     if (rmPromises.length > 0) {
-      Promise.all(rmPromises).then(() => {
+      return Promise.all(rmPromises).then(() => {
         let spliceIndexLow = this._handleAddedSplices(repeat, array, splices);
         updateOverrideContexts(repeat.viewSlot.children, spliceIndexLow);
       });