Prevent flushed results from clearing non-optimistic results

Previously we called clearLayer when clearing an optimistic
mutation result batch, which may erase existing mutation
result data. This shouldn't be possible but we can account
for duplicate mutation results this way and also stop
exposing clearLayer.

exchanges/graphcache/src/cacheExchange.ts

@@ -26,10 +26,9 @@ import {
 } from 'wonka';
 
 import { query, write, writeOptimistic } from './operations';
-import { hydrateData, clearLayer } from './store/data';
 import { makeDict, isDictEmpty } from './helpers/dict';
 import { filterVariables, getMainOperation } from './ast';
-import { Store, noopDataState, reserveLayer } from './store';
+import { Store, noopDataState, hydrateData, reserveLayer } from './store';
 
 import {
   UpdatesConfig,
@@ -404,7 +403,7 @@ export const cacheExchange = (opts?: CacheExchangeOpts): Exchange => ({
           }
 
           for (let i = 0; i < mutationResultBuffer.length; i++) {
-            clearLayer(store.data, mutationResultBuffer[i].operation.key);
+            reserveLayer(store.data, mutationResultBuffer[i].operation.key);
           }
 
           for (const dep in blockedDependencies) {

exchanges/graphcache/src/store/data.ts

@@ -490,7 +490,7 @@ const createLayer = (data: InMemoryData, layerKey: number) => {
 };
 
 /** Clears all links and records of an optimistic layer */
-export const clearLayer = (data: InMemoryData, layerKey: number) => {
+const clearLayer = (data: InMemoryData, layerKey: number) => {
   if (data.refLock[layerKey]) {
     delete data.refLock[layerKey];
     delete data.records.optimistic[layerKey];

exchanges/graphcache/src/store/index.ts

@@ -3,8 +3,8 @@ export {
   clearDataState,
   noopDataState,
   reserveLayer,
-  clearLayer,
   getCurrentDependencies,
+  hydrateData,
 } from './data';
 
 export * from './keys';