Pass previous diff to watch.callback, onWatchUpdated, and onQueryUpda…

…ted.

src/cache/core/cache.ts

@@ -31,7 +31,8 @@ export type BatchOptions<C extends ApolloCache<any>> = {
   onWatchUpdated?: (
     this: C,
     watch: Cache.WatchOptions,
-    diff: Cache.DiffResult<any>,
+    newDiff: Cache.DiffResult<any>,
+    oldDiff?: Cache.DiffResult<any>,
   ) => any;
 };
 

src/cache/core/types/Cache.ts

@@ -2,7 +2,10 @@ import { DataProxy } from './DataProxy';
 import { Modifier, Modifiers } from './common';
 
 export namespace Cache {
-  export type WatchCallback = (diff: Cache.DiffResult<any>) => void;
+  export type WatchCallback = (
+    newDiff: Cache.DiffResult<any>,
+    oldDiff?: Cache.DiffResult<any>,
+  ) => void;
 
   export interface ReadOptions<TVariables = any, TData = any>
     extends DataProxy.Query<TVariables, TData> {

src/cache/inmemory/inMemoryCache.ts

@@ -478,6 +478,7 @@ export class InMemoryCache extends ApolloCache<NormalizedCacheObject> {
     c: Cache.WatchOptions,
     options?: BroadcastOptions,
   ) {
+    const { lastDiff } = c;
     const diff = this.diff<any>({
       query: c.query,
       variables: c.variables,
@@ -491,15 +492,15 @@ export class InMemoryCache extends ApolloCache<NormalizedCacheObject> {
       }
 
       if (options.onWatchUpdated &&
-          options.onWatchUpdated.call(this, c, diff) === false) {
+          options.onWatchUpdated.call(this, c, diff, lastDiff) === false) {
         // Returning false from the onWatchUpdated callback will prevent
         // calling c.callback(diff) for this watcher.
         return;
       }
     }
 
-    if (!c.lastDiff || c.lastDiff.result !== diff.result) {
-      c.callback(c.lastDiff = diff);
+    if (!lastDiff || lastDiff.result !== diff.result) {
+      c.callback(c.lastDiff = diff, lastDiff);
     }
   }
 }

src/core/QueryManager.ts

@@ -1137,14 +1137,14 @@ export class QueryManager<TStore> {
         // temporary optimistic layer, in case that ever matters.
         removeOptimistic,
 
-        onWatchUpdated: onQueryUpdated && function (watch, diff) {
+        onWatchUpdated: onQueryUpdated && function (watch, newDiff, oldDiff) {
           const oq =
             watch.watcher instanceof QueryInfo &&
             watch.watcher.observableQuery;
 
           if (oq) {
             includedQueriesById.delete(oq.queryId);
-            return maybeAddResult(oq, onQueryUpdated(oq, diff));
+            return maybeAddResult(oq, onQueryUpdated(oq, newDiff, oldDiff));
           }
         },
       });

src/core/types.ts

@@ -17,7 +17,8 @@ export type QueryListener = (queryInfo: QueryInfo) => void;
 
 export type OnQueryUpdated<TData> = (
   observableQuery: ObservableQuery,
-  diff: Cache.DiffResult<TData>,
+  newDiff: Cache.DiffResult<TData>,
+  oldDiff?: Cache.DiffResult<TData>,
 ) => boolean | Promise<ApolloQueryResult<TData>>;
 
 export type OperationVariables = Record<string, any>;