Add template annotations

Author: simPod

src/PromiseInterface.php

@@ -2,6 +2,7 @@
 
 namespace React\Promise;
 
+/** @psalm-template T */
 interface PromiseInterface
 {
     /**
@@ -28,9 +29,11 @@ interface PromiseInterface
      *  2. `$onFulfilled` and `$onRejected` will never be called more
      *      than once.
      *
-     * @param callable|null $onFulfilled
-     * @param callable|null $onRejected
-     * @return PromiseInterface
+     * @template TReturn of mixed
+     * 
+     * @param callable(T): TReturn $callable
+     * 
+     * @return (TReturn is PromiseInterface ? TReturn : PromiseInterface<TReturn>)
      */
     public function then(?callable $onFulfilled = null, ?callable $onRejected = null): PromiseInterface;
 
@@ -44,8 +47,9 @@ public function then(?callable $onFulfilled = null, ?callable $onRejected = null
      * Additionally, you can type hint the `$reason` argument of `$onRejected` to catch
      * only specific errors.
      *
-     * @param callable $onRejected
-     * @return PromiseInterface
+     * @param callable(mixed):(PromiseInterface<T>|mixed) $onRejected
+     *
+     * @return PromiseInterface<T>
      */
     public function catch(callable $onRejected): PromiseInterface;
 
@@ -92,7 +96,7 @@ public function catch(callable $onRejected): PromiseInterface;
      * ```
      *
      * @param callable $onFulfilledOrRejected
-     * @return PromiseInterface
+     * @return PromiseInterface<T>
      */
     public function finally(callable $onFulfilledOrRejected): PromiseInterface;