fix(subscription) Updated request return type correctly match apollo-link

[wolfeidau]

Issue #, if available:

Description of changes:

Small change to specify the return type on a method implemented from ApolloLink.

Current type which doesn't compile with apollo-link 1.2.14.

    request(operation: Operation): Observable<unknown>;

New type after change which compiles

    request(operation: Operation): Observable<FetchResult> | null;

Compile error before change was as follows:

ERROR in releases-ui/node_modules/aws-appsync-subscription-link/lib/subscription-handshake-link.d.ts(18,5):
18:5 Property 'request' in type 'SubscriptionHandshakeLink' is not assignable to the same property in base type 'ApolloLink'.
  Type '(operation: Operation) => Observable<unknown>' is not assignable to type '(operation: Operation, forward?: NextLink | undefined) => Observable<FetchResult<{ [key: string]: any; }, Record<string, any>, Record<string, any>>> | null'.
    Type 'Observable<unknown>' is not assignable to type 'Observable<FetchResult<{ [key: string]: any; }, Record<string, any>, Record<string, any>>>'.
      Type 'unknown' is not assignable to type 'FetchResult<{ [key: string]: any; }, Record<string, any>, Record<string, any>>'.
        Type 'unknown' is not assignable to type 'ExecutionResult<{ [key: string]: any; }>'.
    16 |     private clientObservers;
    17 |     constructor(subsInfoContextKey: any);
  > 18 |     request(operation: Operation): Observable<unknown>;
       |     ^
    19 |     connectNewClients(connectionInfo: MqttConnectionInfo[], observer: ZenObservable.Observer<FetchResult>, operation: Operation): Promise<any[]>;
    20 |     connectNewClient(connectionInfo: MqttConnectionInfo, observer: ZenObservable.Observer<FetchResult>, selectionNames: string[]): Promise<any>;
    21 |     subscribeToTopics<T>(client: any, topics: string[], observer: ZenObservable.Observer<T>): Promise<unknown[]>;
Version: typescript 3.9.3

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

✅ 👍 💯

[bcdxn]

I'm still seeing this issue in @apollo/client@3.5.10 and aws-appsync-subscription-link@3.0.10. Is there a workaround to make TypeScript happy until the PR is merged?

[ashika01]

hmm I dont if the typing is right here. Looking at this line, it might be observable of a different type too.

Would you be interested in taking a closer look at this?

[dpilch]

The linked line appears to be type Observable<unknown> since there is no next on the observable. I think we could cast the observable on line 71 to be Observable<FetchResult>.

[VRMink]

I am also seeing this issue
"@apollo/client": "^3.0.0",
"apollo-angular": "^3.0.1",
"aws-appsync-auth-link": "^3.0.7",
"aws-appsync-subscription-link": "^3.1.0",

[dpilch]

Moving to #727