Fix cache.modify() mapping readonly arrays to singular reference (#12983)

Co-authored-by: Jerel Miller <[email protected]>

Author: CarsonF

.api-reports/api-report-cache.api.md

@@ -871,7 +871,7 @@ type StorageType = Record<string, any>;
 export { StoreObject }
 
 // @public (undocumented)
-type StoreObjectValueMaybeReference<StoreVal> = StoreVal extends Array<Record<string, any>> ? StoreVal extends Array<infer Item> ? [
+type StoreObjectValueMaybeReference<StoreVal> = StoreVal extends ReadonlyArray<Record<string, any>> ? StoreVal extends ReadonlyArray<infer Item> ? [
 Item
 ] extends [Record<string, any>] ? ReadonlyArray<AsStoreObject<Item> | Reference> : never : never : StoreVal extends Record<string, any> ? AsStoreObject<StoreVal> | Reference : StoreVal;
 

.api-reports/api-report.api.md

@@ -2514,7 +2514,7 @@ export interface StoreObject {
 // Warning: (ae-forgotten-export) The symbol "AsStoreObject" needs to be exported by the entry point index.d.ts
 //
 // @public (undocumented)
-type StoreObjectValueMaybeReference<StoreVal> = StoreVal extends Array<Record<string, any>> ? StoreVal extends Array<infer Item> ? [
+type StoreObjectValueMaybeReference<StoreVal> = StoreVal extends ReadonlyArray<Record<string, any>> ? StoreVal extends ReadonlyArray<infer Item> ? [
 Item
 ] extends [Record<string, any>] ? ReadonlyArray<AsStoreObject<Item> | Reference> : never : never : StoreVal extends Record<string, any> ? AsStoreObject<StoreVal> | Reference : StoreVal;
 

.changeset/loud-cherries-attend.md

@@ -0,0 +1,5 @@
+---
+"@apollo/client": patch
+---
+
+Fix cache.modify() mapping readonly arrays to singular reference

src/cache/core/__tests__/cache.ts

@@ -559,7 +559,7 @@ describe.skip("Cache type tests", () => {
     test("Allows partial return data", () => {
       const cache = new TestCache();
       cache.modify<{
-        union: Array<
+        union: ReadonlyArray<
           | { __typename: "Type1"; a: string; c: { foo: string } }
           | { __typename: "Type2"; b: string; d: { bar: number } }
         >;

src/cache/core/types/common.ts

@@ -112,8 +112,8 @@ export type Modifier<T> = (
 ) => DeepPartial<T> | DeleteModifier | InvalidateModifier | undefined;
 
 type StoreObjectValueMaybeReference<StoreVal> =
-  StoreVal extends Array<Record<string, any>> ?
-    StoreVal extends Array<infer Item> ?
+  StoreVal extends ReadonlyArray<Record<string, any>> ?
+    StoreVal extends ReadonlyArray<infer Item> ?
       [Item] extends [Record<string, any>] ?
         ReadonlyArray<AsStoreObject<Item> | Reference>
       : never