[@types/when] Restore parameterless when.resolve() and allow (#28593)

parameterless when()

types/when/index.d.ts

@@ -3,6 +3,7 @@
 // Definitions by: Derek Cicerone <https://github.com/derekcicerone>, Wim Looman <https://github.com/Nemo157>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
+declare function When(): When.Promise<void>;
 declare function When<T>(promiseOrValue: T | When.Promise<T> | When.Thenable<T>): When.Promise<T>;
 declare function When<T, U>(promiseOrValue: T | When.Promise<T> | When.Thenable<T>, transform: (val: T) => U): When.Promise<U>;
 
@@ -231,6 +232,7 @@ declare namespace When {
      *    - fulfilled with promiseOrValue's value after it is fulfilled
      *    - rejected with promiseOrValue's reason after it is rejected
      */
+    function resolve(): Promise<void>;
     function resolve<T>(promiseOrValue: T | Promise<T> | Thenable<T>): Promise<T>;
 
     interface Deferred<T> {

types/when/when-tests.ts

@@ -32,6 +32,7 @@ class Data implements IData {
 
 var promise: when.Promise<number>;
 var promise2: when.Promise<Data>;
+var emptyPromise: when.Promise<void>;
 var foreign = new ForeignPromise<number>(1);
 var promiseOrValue = 1 as number | when.Promise<number>;
 var error = new Error("boom!");
@@ -42,6 +43,10 @@ var native: Promise<number>;
  *   Core    *
  * * * * * * */
 
+/* when() */
+
+emptyPromise = when();
+
 /* when(x) */
 
 promise = when(1);
@@ -202,6 +207,10 @@ when.unfold(function (x) {
 promise = when.promise<number>(resolve => resolve(5));
 promise = when.promise<number>((resolve, reject) => reject(error));
 
+/* when.resolve() */
+
+emptyPromise = when.resolve();
+
 /* when.resolve(x) */
 
 promise = when.resolve(1);