fix(base): wait for all chunked requests to arrive before continuing (#…

…4017)

Our previous approach of chunking document availability requests did not wait for all the chunks to finish before returning the results. The debounceCollect utility expects an observable that returns all results in one go, but because we returned a stream that would emit the chunks one-by-one as they arrived, we would only handle the first emission, which would not include the whole result set, breaking assumptions further down the line.

This patch fixes the issue by reducing over each emission, successively add them to an array. (the reduce operator will wait for the stream to finish before emitting a single reduced value).

packages/@sanity/base/src/preview/availability.ts

@@ -1,6 +1,6 @@
 /* eslint-disable max-nested-callbacks */
 import {combineLatest, defer, from, Observable, of} from 'rxjs'
-import {distinctUntilChanged, map, mergeMap, switchMap} from 'rxjs/operators'
+import {distinctUntilChanged, map, mergeMap, reduce, switchMap} from 'rxjs/operators'
 import shallowEquals from 'shallow-equals'
 import {flatten, keyBy} from 'lodash'
 import {getDraftId, getPublishedId} from '../util/draftUtils'
@@ -99,12 +99,23 @@ function chunkDocumentIds(documentIds: string[]): string[][] {
   return chunks
 }
 
+/**
+ * Mutative concat
+ * @param array
+ * @param chunks
+ */
+function mutConcat<T>(array: T[], chunks: T[]) {
+  array.push(...chunks)
+  return array
+}
+
 const fetchDocumentReadability = debounceCollect(function fetchDocumentReadability(
   args: string[][]
 ): Observable<DocumentAvailability[]> {
   const uniqueIds = [...new Set(flatten(args))]
   return from(chunkDocumentIds(uniqueIds)).pipe(
     mergeMap(fetchDocumentReadabilityChunked, 10),
+    reduce(mutConcat, []),
     map((res) => args.map(([id]) => res[uniqueIds.indexOf(id)]))
   )
 },