fix: memoize promise context propagation to avoid safari hangs (#1597)

Author: shakespear-dev

src/common/wrap/wrap-promise.js

@@ -140,13 +140,23 @@ export function wrapPromise (sharedEE) {
 
     promiseEE.on('propagate', function (val, overwrite, trigger) {
       if (!this.getCtx || overwrite) {
-        this.getCtx = function () {
-          // eslint-disable-next-line
-          if (val instanceof Promise) {
-            var store = promiseEE.context(val)
+        const selfStore = this
+        const parentStore =
+          val instanceof Promise ? promiseEE.context(val) : null
+        let cachedCtx
+
+        this.getCtx = function getCtx () {
+          if (cachedCtx) return cachedCtx
+
+          if (parentStore && parentStore !== selfStore) {
+            cachedCtx =
+              typeof parentStore.getCtx === 'function'
+                ? parentStore.getCtx()
+                : parentStore
+          } else {
+            cachedCtx = selfStore
           }
-
-          return store && store.getCtx ? store.getCtx() : this
+          return cachedCtx
         }
       }
     })

tests/components/wrappings/wrap-promise.test.js

@@ -77,6 +77,22 @@ test('Promise then chains are kept separate and distinct', async () => {
   await promise
 })
 
+test('Propagation caches resolved parent context once per chain', async () => {
+  const sentinelCtx = {}
+  const parentPromise = new Promise(resolve => resolve('parent'))
+  const parentStore = promiseEE.context(parentPromise)
+  parentStore.getCtx = jest.fn(() => sentinelCtx)
+
+  const childPromise = parentPromise.then(() => {})
+  const childStore = promiseEE.context(childPromise)
+
+  expect(childStore.getCtx()).toBe(sentinelCtx)
+  expect(childStore.getCtx()).toBe(sentinelCtx)
+  expect(parentStore.getCtx).toHaveBeenCalledTimes(1)
+
+  await childPromise
+})
+
 const thrownError = new Error('123')
 test('A promise constructor exception can be caught', async () => {
   await new Promise(function (resolve, reject) {