Enable strict mode in tsconfig and fix type errors

src/cache/core/types/Cache.ts

@@ -93,7 +93,7 @@ export namespace Cache {
       this: TCache,
       watch: Cache.WatchOptions,
       diff: Cache.DiffResult<any>,
-      lastDiff: Cache.DiffResult<any> | undefined
+      lastDiff?: Cache.DiffResult<any> | undefined
     ) => any;
   }
 

src/cache/inmemory/__tests__/writeToStore.ts

@@ -26,8 +26,13 @@ import { InMemoryCache } from "../inMemoryCache";
 import { withErrorSpy, withWarningSpy } from "../../../testing";
 import { TypedDocumentNode } from "../../../core";
 import { extractFragmentContext } from "../helpers";
+import { KeyFieldsFunction } from "../policies";
+import { invariant } from "../../../utilities/globals";
 
-const getIdField = ({ id }: { id: string }) => id;
+const getIdField: KeyFieldsFunction = ({ id }) => {
+  invariant(typeof id === "string", "id is not a string");
+  return id;
+};
 
 describe("writing to the store", () => {
   const cache = new InMemoryCache({
@@ -1293,19 +1298,17 @@ describe("writing to the store", () => {
     }
 
     testData.forEach((data) => {
-      data.mutation.definitions.forEach(
-        (definition: OperationDefinitionNode) => {
-          if (isOperationDefinition(definition)) {
-            definition.selectionSet.selections.forEach((selection) => {
-              if (isField(selection)) {
-                expect(
-                  storeKeyNameFromField(selection, data.variables)
-                ).toEqual(data.expected);
-              }
-            });
-          }
+      data.mutation.definitions.forEach((definition) => {
+        if (isOperationDefinition(definition)) {
+          definition.selectionSet.selections.forEach((selection) => {
+            if (isField(selection)) {
+              expect(storeKeyNameFromField(selection, data.variables)).toEqual(
+                data.expected
+              );
+            }
+          });
         }
-      );
+      });
     });
   });
 

src/cache/inmemory/entityStore.ts

@@ -548,7 +548,7 @@ class CacheGroup {
 
   // Used by the EntityStore#makeCacheKey method to compute cache keys
   // specific to this CacheGroup.
-  public keyMaker: Trie<object>;
+  public keyMaker!: Trie<object>;
 
   constructor(
     public readonly caching: boolean,
@@ -755,7 +755,11 @@ class Layer extends EntityStore {
   public getStorage(): StorageType {
     let p: EntityStore = this.parent;
     while ((p as Layer).parent) p = (p as Layer).parent;
-    return p.getStorage.apply(p, arguments);
+    return p.getStorage.apply(
+      p,
+      // @ts-expect-error
+      arguments
+    );
   }
 }
 
@@ -778,20 +782,20 @@ class Stump extends Layer {
     return this;
   }
 
-  public merge() {
+  public merge(older: string | StoreObject, newer: string | StoreObject) {
     // We never want to write any data into the Stump, so we forward any merge
     // calls to the Root instead. Another option here would be to throw an
     // exception, but the toReference(object, true) function can sometimes
     // trigger Stump writes (which used to be Root writes, before the Stump
     // concept was introduced).
-    return this.parent.merge.apply(this.parent, arguments);
+    return this.parent.merge(older, newer);
   }
 }
 
 function storeObjectReconciler(
   existingObject: StoreObject,
   incomingObject: StoreObject,
-  property: string
+  property: string | number
 ): StoreValue {
   const existingValue = existingObject[property];
   const incomingValue = incomingObject[property];

src/cache/inmemory/fixPolyfills.native.ts

@@ -33,10 +33,10 @@ try {
   // https://github.com/apollographql/react-apollo/issues/2442#issuecomment-426489517
   testMap.set(frozen, frozen).delete(frozen);
 } catch {
-  const wrap = (method: <T>(obj: T) => T): typeof method => {
+  const wrap = <M extends <T>(obj: T) => T>(method: M): M => {
     return (
       method &&
-      ((obj) => {
+      (((obj) => {
         try {
           // If .set succeeds, also call .delete to avoid leaking memory.
           testMap.set(obj, obj).delete(obj);
@@ -45,7 +45,7 @@ try {
           // by this return-from-finally statement:
           return method.call(Object, obj);
         }
-      })
+      }) as M)
     );
   };
   Object.freeze = wrap(Object.freeze);

src/cache/inmemory/fragmentRegistry.ts

@@ -6,6 +6,7 @@ import type {
 } from "graphql";
 import { visit } from "graphql";
 
+import type { OptimisticWrapperFunction } from "optimism";
 import { wrap } from "optimism";
 
 import type { FragmentMap } from "../../utilities/index.js";
@@ -29,24 +30,22 @@ export function createFragmentRegistry(
   return new FragmentRegistry(...fragments);
 }
 
-const { forEach: arrayLikeForEach } = Array.prototype;
-
 class FragmentRegistry implements FragmentRegistryAPI {
   private registry: FragmentMap = Object.create(null);
 
-  // Call static method FragmentRegistry.from(...) instead of invoking the
+  // Call `createFragmentRegistry` instead of invoking the
   // FragmentRegistry constructor directly. This reserves the constructor for
   // future configuration of the FragmentRegistry.
   constructor(...fragments: DocumentNode[]) {
     this.resetCaches();
     if (fragments.length) {
-      this.register.apply(this, fragments);
+      this.register(...fragments);
     }
   }
 
-  public register(): this {
+  public register(...fragments: DocumentNode[]): this {
     const definitions = new Map<string, FragmentDefinitionNode>();
-    arrayLikeForEach.call(arguments, (doc: DocumentNode) => {
+    fragments.forEach((doc: DocumentNode) => {
       getFragmentDefinitions(doc).forEach((node) => {
         definitions.set(node.name.value, node);
       });
@@ -66,27 +65,15 @@ class FragmentRegistry implements FragmentRegistryAPI {
   private invalidate(name: string) {}
 
   public resetCaches() {
-    this.invalidate = (this.lookup = this.cacheUnaryMethod("lookup")).dirty; // This dirty function is bound to the wrapped lookup method.
-    this.transform = this.cacheUnaryMethod("transform");
-    this.findFragmentSpreads = this.cacheUnaryMethod("findFragmentSpreads");
+    this.invalidate = (this.lookup = this.cacheUnaryMethod(this.lookup)).dirty; // This dirty function is bound to the wrapped lookup method.
+    this.transform = this.cacheUnaryMethod(this.transform);
+    this.findFragmentSpreads = this.cacheUnaryMethod(this.findFragmentSpreads);
   }
 
-  private cacheUnaryMethod<
-    TName extends keyof Pick<
-      FragmentRegistry,
-      "lookup" | "transform" | "findFragmentSpreads"
-    >,
-  >(name: TName) {
-    const registry = this;
-    const originalMethod = FragmentRegistry.prototype[name];
-    return wrap(
-      function () {
-        return originalMethod.apply(registry, arguments);
-      },
-      {
-        makeCacheKey: (arg) => arg,
-      }
-    );
+  private cacheUnaryMethod<F extends (arg: any) => any>(originalMethod: F) {
+    return wrap<Parameters<F>, ReturnType<F>>(originalMethod.bind(this), {
+      makeCacheKey: (arg) => arg,
+    }) as OptimisticWrapperFunction<Parameters<F>, ReturnType<F>> & F;
   }
 
   public lookup(fragmentName: string): FragmentDefinitionNode | null {

src/cache/inmemory/inMemoryCache.ts

@@ -33,18 +33,18 @@ type BroadcastOptions = Pick<
 >;
 
 export class InMemoryCache extends ApolloCache<NormalizedCacheObject> {
-  private data: EntityStore;
-  private optimisticData: EntityStore;
+  private data!: EntityStore;
+  private optimisticData!: EntityStore;
 
   protected config: InMemoryCacheConfig;
   private watches = new Set<Cache.WatchOptions>();
   private addTypename: boolean;
 
-  private storeReader: StoreReader;
-  private storeWriter: StoreWriter;
+  private storeReader!: StoreReader;
+  private storeWriter!: StoreWriter;
   private addTypenameTransform = new DocumentTransform(addTypenameToDocument);
 
-  private maybeBroadcastWatch: OptimisticWrapperFunction<
+  private maybeBroadcastWatch!: OptimisticWrapperFunction<
     [Cache.WatchOptions, BroadcastOptions?],
     any,
     [Cache.WatchOptions]

src/cache/inmemory/readFromStore.ts

@@ -535,7 +535,7 @@ function firstMissing(tree: MissingTree): string | undefined {
       return value;
     });
   } catch (result) {
-    return result;
+    return result as string;
   }
 }
 

src/core/ApolloClient.ts

@@ -86,7 +86,7 @@ export class ApolloClient<TCacheShape> implements DataProxy {
   public readonly typeDefs: ApolloClientOptions<TCacheShape>["typeDefs"];
 
   private queryManager: QueryManager<TCacheShape>;
-  private devToolsHookCb: Function;
+  private devToolsHookCb?: Function;
   private resetStoreCallbacks: Array<() => Promise<any>> = [];
   private clearStoreCallbacks: Array<() => Promise<any>> = [];
   private localState: LocalState<TCacheShape>;
@@ -586,11 +586,33 @@ export class ApolloClient<TCacheShape> implements DataProxy {
    * re-execute any queries then you should make sure to stop watching any
    * active queries.
    */
+  public refetchQueries<TResult = Promise<ApolloQueryResult<any>>>(
+    options: RefetchQueriesOptions<ApolloCache<TCacheShape>, TResult>
+  ): RefetchQueriesResult<TResult>;
+
+  /**
+   * @deprecated The two-generics version of refetchQueries is deprecated
+   * and will be removed in the next major version.
+   *
+   * Please use the single-generic version only specifying the return type instead.
+   *
+   * The first generic argument of this overload is essentially an
+   * `cache as any as TCache`
+   * assertion and does not give you any type safety.
+   *
+   * If you rely on a specific cache implementation, please do an `instanceof` check
+   * in your runtime code to narrow down the type in a type-safe manner.
+   */
   public refetchQueries<
-    TCache extends ApolloCache<any> = ApolloCache<TCacheShape>,
-    TResult = Promise<ApolloQueryResult<any>>,
+    /** @deprecated */
+    TCache extends ApolloCache<any>,
+    TResult,
   >(
     options: RefetchQueriesOptions<TCache, TResult>
+  ): RefetchQueriesResult<TResult>;
+
+  public refetchQueries<TResult>(
+    options: RefetchQueriesOptions<ApolloCache<TCacheShape>, TResult>
   ): RefetchQueriesResult<TResult> {
     const map = this.queryManager.refetchQueries(options);
     const queries: ObservableQuery<any>[] = [];

src/core/LocalState.ts

@@ -75,9 +75,9 @@ export type LocalStateOptions<TCacheShape> = {
 
 export class LocalState<TCacheShape> {
   private cache: ApolloCache<TCacheShape>;
-  private client: ApolloClient<TCacheShape>;
+  private client?: ApolloClient<TCacheShape>;
   private resolvers?: Resolvers;
-  private fragmentMatcher: FragmentMatcher;
+  private fragmentMatcher?: FragmentMatcher;
   private selectionsToResolveCache = new WeakMap<
     ExecutableDefinitionNode,
     Set<SelectionNode>
@@ -162,7 +162,7 @@ export class LocalState<TCacheShape> {
     this.fragmentMatcher = fragmentMatcher;
   }
 
-  public getFragmentMatcher(): FragmentMatcher {
+  public getFragmentMatcher(): FragmentMatcher | undefined {
     return this.fragmentMatcher;
   }
 
@@ -197,11 +197,11 @@ export class LocalState<TCacheShape> {
   // To support `@client @export(as: "someVar")` syntax, we'll first resolve
   // @client @export fields locally, then pass the resolved values back to be
   // used alongside the original operation variables.
-  public async addExportedVariables(
+  public async addExportedVariables<TVars extends OperationVariables>(
     document: DocumentNode,
-    variables: OperationVariables = {},
+    variables: TVars = {} as TVars,
     context = {}
-  ) {
+  ): /* returns at least the variables that were passed in */ Promise<TVars> {
     if (document) {
       return this.resolveDocument(
         document,

src/core/ObservableQuery.ts

@@ -928,7 +928,9 @@ Did you mean to call refetch(variables) instead of refetch({ variables })?`,
     newOptions?: Partial<WatchQueryOptions<TVariables, TData>>,
     newNetworkStatus?: NetworkStatus
   ) {
-    return this.reobserveAsConcast(newOptions, newNetworkStatus).promise;
+    return this.reobserveAsConcast(newOptions, newNetworkStatus).promise.then(
+      ensureResult
+    );
   }
 
   public resubscribeAfterError(
@@ -1051,14 +1053,18 @@ export function reobserveCacheFirst<TData, TVars extends OperationVariables>(
       fetchPolicy: "cache-first",
       // Use a temporary nextFetchPolicy function that replaces itself with the
       // previous nextFetchPolicy value and returns the original fetchPolicy.
-      nextFetchPolicy(this: WatchQueryOptions<TVars, TData>) {
+      nextFetchPolicy(
+        this: WatchQueryOptions<TVars, TData>,
+        currentFetchPolicy: WatchQueryFetchPolicy,
+        context: NextFetchPolicyContext<TData, TVars>
+      ) {
         // Replace this nextFetchPolicy function in the options object with the
         // original this.options.nextFetchPolicy value.
         this.nextFetchPolicy = nextFetchPolicy;
         // If the original nextFetchPolicy value was a function, give it a
         // chance to decide what happens here.
-        if (typeof nextFetchPolicy === "function") {
-          return nextFetchPolicy.apply(this, arguments);
+        if (typeof this.nextFetchPolicy === "function") {
+          return this.nextFetchPolicy(currentFetchPolicy, context);
         }
         // Otherwise go back to the original this.options.fetchPolicy.
         return fetchPolicy!;
@@ -1090,3 +1096,13 @@ function skipCacheDataFor(
     fetchPolicy === "standby"
   );
 }
+
+export function ensureResult<TData = any>(
+  value: ApolloQueryResult<TData> | undefined
+): ApolloQueryResult<TData> {
+  invariant(
+    value,
+    "A Concast finished without a result. This in an Apollo Client bug, please file a bug report."
+  );
+  return value;
+}

src/core/QueryInfo.ts

@@ -50,6 +50,7 @@ function wrapDestructiveCacheMethod(
         // that matters in any conceivable practical scenario.
         (destructiveMethodCounts.get(cache)! + 1) % 1e15
       );
+      // @ts-expect-error this is just too generic to be typed correctly
       return original.apply(this, arguments);
     };
   }
@@ -113,7 +114,7 @@ export class QueryInfo {
     // NetworkStatus.loading, but also possibly fetchMore, poll, refetch,
     // or setVariables.
     networkStatus?: NetworkStatus;
-    observableQuery?: ObservableQuery<any>;
+    observableQuery?: ObservableQuery<any, any>;
     lastRequestId?: number;
   }): this {
     let networkStatus = query.networkStatus || NetworkStatus.loading;
@@ -214,10 +215,10 @@ export class QueryInfo {
     }
   }
 
-  public readonly observableQuery: ObservableQuery<any> | null = null;
+  public readonly observableQuery: ObservableQuery<any, any> | null = null;
   private oqListener?: QueryListener;
 
-  setObservableQuery(oq: ObservableQuery<any> | null) {
+  setObservableQuery(oq: ObservableQuery<any, any> | null) {
     if (oq === this.observableQuery) return;
 
     if (this.oqListener) {