Type-safe callable functions with generics

spec/v1/providers/https.spec.ts

@@ -115,7 +115,7 @@ describe("#onCall", () => {
   });
 
   it("has a .run method", () => {
-    const cf = https.onCall((d, c) => {
+    const cf = https.onCall<string, { data: string; context: https.CallableContext }>((d, c) => {
       return { data: d, context: c };
     });
 

spec/v2/providers/https.spec.ts

@@ -454,8 +454,8 @@ describe("onCall", () => {
     https.onCall<string, string>(
       (request: https.CallableRequest<string>) => `hello, ${request.data}!`
     );
-    https.onCall<string>((request: https.CallableRequest<string>) => `hello, ${request.data}!`);
-    https.onCall<string>((request: https.CallableRequest) => `hello, ${request.data}!`);
+    https.onCall<string, string>((request) => `hello, ${request.data}!`);
+    https.onCall<string, string>((request) => `hello, ${request.data}!`);
     https.onCall((request: https.CallableRequest<string>) => `Hello, ${request.data}`);
     https.onCall((request: https.CallableRequest) => `Hello, ${request.data}`);
   });

src/v1/function-builder.ts

@@ -340,8 +340,9 @@ export class FunctionBuilder {
        * Declares a callable method for clients to call using a Firebase SDK.
        * @param handler A method that takes a data and context and returns a value.
        */
-      onCall: (handler: (data: any, context: https.CallableContext) => any | Promise<any>) =>
-        https._onCallWithOptions(handler, this.options),
+      onCall: <TData = never, TReturn = never>(
+        handler: (data: TData, context: https.CallableContext) => TReturn | Promise<TReturn>
+      ) => https._onCallWithOptions(handler, this.options),
     };
   }
 

src/v1/providers/https.ts

@@ -51,9 +51,9 @@ export function onRequest(
  * Declares a callable method for clients to call using a Firebase SDK.
  * @param handler A method that takes a data and context and returns a value.
  */
-export function onCall(
-  handler: (data: any, context: CallableContext) => any | Promise<any>
-): HttpsFunction & Runnable<any> {
+export function onCall<TData = never, TReturn = never>(
+  handler: (data: TData, context: CallableContext) => TReturn | Promise<TReturn>
+): HttpsFunction & Runnable<TData> {
   return _onCallWithOptions(handler, {});
 }
 

src/v2/providers/https.ts

@@ -187,12 +187,12 @@ export type HttpsFunction = ((
 /**
  * Creates a callable method for clients to call using a Firebase SDK.
  */
-export interface CallableFunction<T, Return> extends HttpsFunction {
+export interface CallableFunction<T, TReturn> extends HttpsFunction {
   /** Executes the handler function with the provided data as input. Used for unit testing.
    * @param data - An input for the handler function.
    * @returns The output of the handler function.
    */
-  run(data: CallableRequest<T>): Return;
+  run(data: CallableRequest<T>): TReturn;
 }
 /**
  * Handles HTTPS requests.
@@ -299,26 +299,26 @@ export function onRequest(
  * @param handler - A function that takes a {@link https.CallableRequest}.
  * @returns A function that you can export and deploy.
  */
-export function onCall<T = any, Return = any | Promise<any>>(
+export function onCall<T = never, TReturn = never>(
   opts: CallableOptions,
-  handler: (request: CallableRequest<T>) => Return
-): CallableFunction<T, Return>;
+  handler: (request: CallableRequest<T>) => TReturn | Promise<TReturn>
+): CallableFunction<T, TReturn | Promise<TReturn>>;
 /**
  * Declares a callable method for clients to call using a Firebase SDK.
  * @param handler - A function that takes a {@link https.CallableRequest}.
  * @returns A function that you can export and deploy.
  */
-export function onCall<T = any, Return = any | Promise<any>>(
-  handler: (request: CallableRequest<T>) => Return
-): CallableFunction<T, Return>;
-export function onCall<T = any, Return = any | Promise<any>>(
-  optsOrHandler: CallableOptions | ((request: CallableRequest<T>) => Return),
-  handler?: (request: CallableRequest<T>) => Return
-): CallableFunction<T, Return> {
+export function onCall<T = never, TReturn = never>(
+  handler: (request: CallableRequest<T>) => TReturn | Promise<TReturn>
+): CallableFunction<T, TReturn | Promise<TReturn>>;
+export function onCall<T = never, TReturn = never>(
+  optsOrHandler: CallableOptions | ((request: CallableRequest<T>) => TReturn | Promise<TReturn>),
+  handler?: (request: CallableRequest<T>) => TReturn | Promise<TReturn>
+): CallableFunction<T, TReturn | Promise<TReturn>> {
   let opts: CallableOptions;
   if (arguments.length === 1) {
     opts = {};
-    handler = optsOrHandler as (request: CallableRequest<T>) => Return;
+    handler = optsOrHandler as (request: CallableRequest<T>) => TReturn | Promise<TReturn>;
   } else {
     opts = optsOrHandler as CallableOptions;
   }