Run Policies's merge before cache merge

src/cache/inmemory/__tests__/writeToStore.ts

@@ -2496,6 +2496,20 @@ describe('writing to the store', () => {
         },
       },
 
+      {
+        existing:  {
+          __ref: "Account:12345",
+        },
+        incoming:  {
+          __typename: "Account",
+          contact: "[email protected]",
+          id: 12345,
+        },
+        merged:  {
+          __ref: "Account:12345",
+        },
+      },
+
       {
         existing: {
           __typename: "Account",

src/cache/inmemory/policies.ts

@@ -226,6 +226,8 @@ export interface FieldFunctionOptions<
   // helper function can be used to merge objects in a way that respects any
   // custom merge functions defined for their fields.
   mergeObjects: MergeObjectsFunction;
+
+  context: ReadMergeModifyContext | undefined;
 }
 
 type MergeObjectsFunction = <T extends StoreObject | Reference>(
@@ -542,7 +544,7 @@ export class Policies {
     });
   }
 
-  private getTypePolicy(typename: string): Policies["typePolicies"][string] {
+  public getTypePolicy(typename: string): Policies["typePolicies"][string] {
     if (!hasOwn.call(this.typePolicies, typename)) {
       const policy: Policies["typePolicies"][string] =
         this.typePolicies[typename] = Object.create(null);
@@ -878,7 +880,7 @@ export class Policies {
       // that need to deduplicate child objects and references.
       void 0,
       { typename,
-        fieldName: field.name.value,
+        fieldName: field?.name.value || "ROOT",
         field,
         variables: context.variables },
       context,
@@ -917,6 +919,7 @@ function makeFieldFunctionOptions(
       );
     },
     mergeObjects: makeMergeObjectsFunction(context.store),
+    context
   };
 }
 

src/cache/inmemory/types.ts

@@ -133,7 +133,7 @@ export interface InMemoryCacheConfig extends ApolloReducerConfig {
 }
 
 export interface MergeInfo {
-  field: FieldNode;
+  field: FieldNode | undefined;
   typename: string | undefined;
   merge: FieldMergeFunction;
 };

src/cache/inmemory/writeToStore.ts

@@ -154,7 +154,7 @@ export class StoreWriter {
     context.incomingById.forEach(({ storeObject, mergeTree, fieldNodeSet }, dataId) => {
       const entityRef = makeReference(dataId);
 
-      if (mergeTree && mergeTree.map.size) {
+      if (mergeTree && (mergeTree.map.size || mergeTree.info)) {
         const applied = this.applyMerges(mergeTree, entityRef, storeObject, context);
         if (isReference(applied)) {
           // Assume References returned by applyMerges have already been merged
@@ -421,6 +421,24 @@ export class StoreWriter {
         previous.mergeTree = mergeMergeTrees(previous.mergeTree, mergeTree);
         fieldNodeSet.forEach(field => previous.fieldNodeSet.add(field));
       } else {
+
+        if(typename && mergeTreeIsEmpty(mergeTree)) {
+          const typePolicy = policies.getTypePolicy(
+            typename,
+          );
+
+          const merge = typePolicy.merge
+
+          if (merge) {
+            mergeTree.info = {
+              field: undefined as any, // !!!
+              typename,
+              merge,
+            };
+          }
+        }
+
+
         context.incomingById.set(dataId, {
           storeObject: incoming,
           // Save a reference to mergeTree only if it is not empty, because
@@ -660,6 +678,9 @@ export class StoreWriter {
     }
 
     if (mergeTree.info) {
+      if(isReference(existing) && isReference(incoming)){
+        return incoming;
+      }
       return this.cache.policies.runMergeFunction(
         existing,
         incoming,

src/utilities/policies/__tests__/relayStylePagination.test.ts

@@ -130,6 +130,7 @@ describe('relayStylePagination', () => {
       readField: () => undefined,
       canRead: () => false,
       mergeObjects: (existing, _incoming) => existing,
+      context: undefined,
     };
 
     it('should maintain endCursor and startCursor with empty edges', () => {