AsyncReturnType: Add support for PromiseLike (#1082)

Author: christophehurpeau

source/async-return-type.d.ts

@@ -1,4 +1,4 @@
-type AsyncFunction = (...arguments_: any[]) => Promise<unknown>;
+type AsyncFunction = (...arguments_: any[]) => PromiseLike<unknown>;
 
 /**
 Unwrap the return type of a function that returns a `Promise`.

test-d/async-return-type.ts

@@ -11,3 +11,14 @@ asyncFunction().then(value => { // eslint-disable-line unicorn/prefer-top-level-
 	expectType<Value>(value);
 	expectNotAssignable<string>(value);
 });
+
+function asyncPromiseLike(): PromiseLike<number> {
+	return Promise.resolve(2);
+}
+
+type ValuePromiseLike = AsyncReturnType<typeof asyncPromiseLike>;
+
+asyncPromiseLike().then(value => { // eslint-disable-line unicorn/prefer-top-level-await, @typescript-eslint/no-floating-promises
+	expectType<ValuePromiseLike>(value);
+	expectNotAssignable<string>(value);
+});