Add template annotations

These annotations will aid static analyses like PHPStan and Psalm to
enhance type-safety for this project and projects depending on it

These changes make the following example understandable by PHPStan:

```php
final readonly class User
{
    public function __construct(
        public string $name,
    )
}

/**
 * \React\Promise\PromiseInterface<User>
 */
function getCurrentUserFromDatabase(): \React\Promise\PromiseInterface
{
    // The following line would do the database query and fetch the
result from it
    // but keeping it simple for the sake of the example.
    return \React\Promise\resolve(new User('WyriHaximus'));
}

// For the sake of this example we're going to assume the following code
runs
// in \React\Async\async call
echo await(getCurrentUserFromDatabase())->name; // This echos:
WyriHaximus
```

README.md

@@ -57,7 +57,7 @@ Async\await(…);
 
 ### await()
 
-The `await(PromiseInterface $promise): mixed` function can be used to
+The `await(PromiseInterface<T> $promise): T` function can be used to
 block waiting for the given `$promise` to be fulfilled.
 
 ```php
@@ -94,7 +94,7 @@ try {
 
 ### coroutine()
 
-The `coroutine(callable $function, mixed ...$args): PromiseInterface<mixed>` function can be used to
+The `coroutine(callable(mixed ...$args):(\Generator|PromiseInterface<T>|T) $function, mixed ...$args): PromiseInterface<T>` function can be used to
 execute a Generator-based coroutine to "await" promises.
 
 ```php
@@ -277,7 +277,7 @@ trigger at the earliest possible time in the future.
 
 ### parallel()
 
-The `parallel(iterable<callable():PromiseInterface<mixed>> $tasks): PromiseInterface<array<mixed>>` function can be used
+The `parallel(iterable<callable():PromiseInterface<T>> $tasks): PromiseInterface<array<T>>` function can be used
 like this:
 
 ```php
@@ -319,7 +319,7 @@ React\Async\parallel([
 
 ### series()
 
-The `series(iterable<callable():PromiseInterface<mixed>> $tasks): PromiseInterface<array<mixed>>` function can be used
+The `series(iterable<callable():PromiseInterface<T>> $tasks): PromiseInterface<array<T>>` function can be used
 like this:
 
 ```php
@@ -361,7 +361,7 @@ React\Async\series([
 
 ### waterfall()
 
-The `waterfall(iterable<callable(mixed=):PromiseInterface<mixed>> $tasks): PromiseInterface<mixed>` function can be used
+The `waterfall(iterable<callable(mixed=):PromiseInterface<T>> $tasks): PromiseInterface<T>` function can be used
 like this:
 
 ```php

src/functions.php

@@ -44,8 +44,9 @@
  * }
  * ```
  *
- * @param PromiseInterface $promise
- * @return mixed returns whatever the promise resolves to
+ * @template T
+ * @param PromiseInterface<T> $promise
+ * @return T returns whatever the promise resolves to
  * @throws \Exception when the promise is rejected with an `Exception`
  * @throws \Throwable when the promise is rejected with a `Throwable`
  * @throws \UnexpectedValueException when the promise is rejected with an unexpected value (Promise API v1 or v2 only)
@@ -93,13 +94,14 @@ function ($error) use (&$exception, &$rejected, &$wait, &$loopStarted) {
         // promise is rejected with an unexpected value (Promise API v1 or v2 only)
         if (!$exception instanceof \Throwable) {
             $exception = new \UnexpectedValueException(
-                'Promise rejected with unexpected value of type ' . (is_object($exception) ? get_class($exception) : gettype($exception))
+                'Promise rejected with unexpected value of type ' . (is_object($exception) ? get_class($exception) : gettype($exception)) // @phpstan-ignore-line
             );
         }
 
         throw $exception;
     }
 
+    /** @var T $resolved */
     return $resolved;
 }
 
@@ -296,9 +298,16 @@ function delay(float $seconds): void
  * });
  * ```
  *
- * @param callable(mixed ...$args):(\Generator<mixed,PromiseInterface,mixed,mixed>|mixed) $function
+ * @template T
+ * @template TYield
+ * @template A1 (any number of function arguments, see https://github.com/phpstan/phpstan/issues/8214)
+ * @template A2
+ * @template A3
+ * @template A4
+ * @template A5
+ * @param callable(A1, A2, A3, A4, A5):(\Generator<mixed, PromiseInterface<TYield>, TYield, PromiseInterface<T>|T>|PromiseInterface<T>|T) $function
  * @param mixed ...$args Optional list of additional arguments that will be passed to the given `$function` as is
- * @return PromiseInterface<mixed>
+ * @return PromiseInterface<T>
  * @since 3.0.0
  */
 function coroutine(callable $function, ...$args): PromiseInterface
@@ -315,7 +324,7 @@ function coroutine(callable $function, ...$args): PromiseInterface
 
     $promise = null;
     $deferred = new Deferred(function () use (&$promise) {
-        /** @var ?PromiseInterface $promise */
+        /** @var ?PromiseInterface<T> $promise */
         if ($promise instanceof PromiseInterface && \method_exists($promise, 'cancel')) {
             $promise->cancel();
         }
@@ -336,7 +345,6 @@ function coroutine(callable $function, ...$args): PromiseInterface
             return;
         }
 
-        /** @var mixed $promise */
         $promise = $generator->current();
         if (!$promise instanceof PromiseInterface) {
             $next = null;
@@ -346,6 +354,7 @@ function coroutine(callable $function, ...$args): PromiseInterface
             return;
         }
 
+        /** @var PromiseInterface<TYield> $promise */
         assert($next instanceof \Closure);
         $promise->then(function ($value) use ($generator, $next) {
             $generator->send($value);
@@ -364,12 +373,13 @@ function coroutine(callable $function, ...$args): PromiseInterface
 }
 
 /**
- * @param iterable<callable():PromiseInterface<mixed>> $tasks
- * @return PromiseInterface<array<mixed>>
+ * @template T
+ * @param iterable<callable():(PromiseInterface<T>|T)> $tasks
+ * @return PromiseInterface<array<T>>
  */
 function parallel(iterable $tasks): PromiseInterface
 {
-    /** @var array<int,PromiseInterface> $pending */
+    /** @var array<int,PromiseInterface<T>> $pending */
     $pending = [];
     $deferred = new Deferred(function () use (&$pending) {
         foreach ($pending as $promise) {
@@ -424,14 +434,15 @@ function parallel(iterable $tasks): PromiseInterface
 }
 
 /**
- * @param iterable<callable():PromiseInterface<mixed>> $tasks
- * @return PromiseInterface<array<mixed>>
+ * @template T
+ * @param iterable<callable():(PromiseInterface<T>|T)> $tasks
+ * @return PromiseInterface<array<T>>
  */
 function series(iterable $tasks): PromiseInterface
 {
     $pending = null;
     $deferred = new Deferred(function () use (&$pending) {
-        /** @var ?PromiseInterface $pending */
+        /** @var ?PromiseInterface<T> $pending */
         if ($pending instanceof PromiseInterface && \method_exists($pending, 'cancel')) {
             $pending->cancel();
         }
@@ -478,14 +489,15 @@ function series(iterable $tasks): PromiseInterface
 }
 
 /**
- * @param iterable<(callable():PromiseInterface<mixed>)|(callable(mixed):PromiseInterface<mixed>)> $tasks
- * @return PromiseInterface<mixed>
+ * @template T
+ * @param iterable<(callable():(PromiseInterface<T>|T))|(callable(mixed):(PromiseInterface<T>|T))> $tasks
+ * @return PromiseInterface<($tasks is non-empty-array|\Traversable ? T : null)>
  */
 function waterfall(iterable $tasks): PromiseInterface
 {
     $pending = null;
     $deferred = new Deferred(function () use (&$pending) {
-        /** @var ?PromiseInterface $pending */
+        /** @var ?PromiseInterface<T> $pending */
         if ($pending instanceof PromiseInterface && \method_exists($pending, 'cancel')) {
             $pending->cancel();
         }

tests/CoroutineTest.php

@@ -22,7 +22,7 @@ public function testCoroutineReturnsFulfilledPromiseIfFunctionReturnsImmediately
     {
         $promise = coroutine(function () {
             if (false) { // @phpstan-ignore-line
-                yield;
+                yield resolve(null);
             }
             return 42;
         });
@@ -53,7 +53,7 @@ public function testCoroutineReturnsRejectedPromiseIfFunctionThrowsImmediately()
     {
         $promise = coroutine(function () {
             if (false) { // @phpstan-ignore-line
-                yield;
+                yield resolve(null);
             }
             throw new \RuntimeException('Foo');
         });
@@ -99,7 +99,7 @@ public function testCoroutineReturnsFulfilledPromiseIfFunctionReturnsAfterYieldi
 
     public function testCoroutineReturnsRejectedPromiseIfFunctionYieldsInvalidValue(): void
     {
-        $promise = coroutine(function () {
+        $promise = coroutine(function () { // @phpstan-ignore-line
             yield 42;
         });
 
@@ -169,7 +169,7 @@ public function testCoroutineShouldNotCreateAnyGarbageReferencesWhenGeneratorRet
 
         $promise = coroutine(function () {
             if (false) { // @phpstan-ignore-line
-                yield;
+                yield resolve(null);
             }
             return 42;
         });
@@ -249,7 +249,7 @@ public function testCoroutineShouldNotCreateAnyGarbageReferencesWhenGeneratorYie
 
         gc_collect_cycles();
 
-        $promise = coroutine(function () {
+        $promise = coroutine(function () { // @phpstan-ignore-line
             yield 42;
         });
 

tests/ParallelTest.php

@@ -12,6 +12,9 @@ class ParallelTest extends TestCase
 {
     public function testParallelWithoutTasks(): void
     {
+        /**
+         * @var array<callable(): React\Promise\PromiseInterface<mixed>> $tasks
+         */
         $tasks = array();
 
         $promise = React\Async\parallel($tasks);

tests/SeriesTest.php

@@ -12,6 +12,9 @@ class SeriesTest extends TestCase
 {
     public function testSeriesWithoutTasks(): void
     {
+        /**
+         * @var array<callable(): React\Promise\PromiseInterface<mixed>> $tasks
+         */
         $tasks = array();
 
         $promise = React\Async\series($tasks);
@@ -152,6 +155,9 @@ public function testSeriesWithErrorFromInfiniteIteratorAggregateReturnsPromiseRe
             /** @var int */
             public $called = 0;
 
+            /**
+             * @return \Iterator<callable(): React\Promise\PromiseInterface<mixed>>
+             */
             public function getIterator(): \Iterator
             {
                 while (true) { // @phpstan-ignore-line

tests/WaterfallTest.php

@@ -12,6 +12,9 @@ class WaterfallTest extends TestCase
 {
     public function testWaterfallWithoutTasks(): void
     {
+        /**
+         * @var array<callable(): React\Promise\PromiseInterface<mixed>> $tasks
+         */
         $tasks = array();
 
         $promise = React\Async\waterfall($tasks);
@@ -166,6 +169,9 @@ public function testWaterfallWithErrorFromInfiniteIteratorAggregateReturnsPromis
             /** @var int */
             public $called = 0;
 
+            /**
+             * @return \Iterator<callable(): React\Promise\PromiseInterface<mixed>>
+             */
             public function getIterator(): \Iterator
             {
                 while (true) { // @phpstan-ignore-line

tests/types/await.php

@@ -0,0 +1,19 @@
+<?php
+
+use React\Promise\PromiseInterface;
+use function PHPStan\Testing\assertType;
+use function React\Async\await;
+use function React\Promise\resolve;
+
+assertType('bool', await(resolve(true)));
+
+final class AwaitExampleUser
+{
+    public string $name;
+
+    public function __construct(string $name) {
+        $this->name = $name;
+    }
+}
+
+assertType('string', await(resolve(new AwaitExampleUser('WyriHaximus')))->name);

tests/types/coroutine.php

@@ -0,0 +1,60 @@
+<?php
+
+use function PHPStan\Testing\assertType;
+use function React\Async\await;
+use function React\Async\coroutine;
+use function React\Promise\resolve;
+
+assertType('React\Promise\PromiseInterface<bool>', coroutine(static function () {
+    return true;
+}));
+
+assertType('React\Promise\PromiseInterface<bool>', coroutine(static function () {
+    return resolve(true);
+}));
+
+// assertType('React\Promise\PromiseInterface<bool>', coroutine(static function () {
+//     return (yield resolve(true));
+// }));
+
+assertType('React\Promise\PromiseInterface<int>', coroutine(static function () {
+//     $bool = yield resolve(true);
+//     assertType('bool', $bool);
+
+    return time();
+}));
+
+// assertType('React\Promise\PromiseInterface<bool>', coroutine(static function () {
+//     $bool = yield resolve(true);
+//     assertType('bool', $bool);
+
+//     return $bool;
+// }));
+
+assertType('React\Promise\PromiseInterface<bool>', coroutine(static function () {
+    yield resolve(time());
+
+    return true;
+}));
+
+assertType('React\Promise\PromiseInterface<bool>', coroutine(static function () {
+    for ($i = 0; $i <= 10; $i++) {
+        yield resolve($i);
+    }
+
+    return true;
+}));
+
+assertType('React\Promise\PromiseInterface<int>', coroutine(static fn(int $a): int => $a, 42));
+assertType('React\Promise\PromiseInterface<int>', coroutine(static fn(int $a, int $b): int => $a + $b, 10, 32));
+assertType('React\Promise\PromiseInterface<int>', coroutine(static fn(int $a, int $b, int $c): int => $a + $b + $c, 10, 22, 10));
+assertType('React\Promise\PromiseInterface<int>', coroutine(static fn(int $a, int $b, int $c, int $d): int => $a + $b + $c + $d, 10, 22, 5, 5));
+assertType('React\Promise\PromiseInterface<int>', coroutine(static fn(int $a, int $b, int $c, int $d, int $e): int => $a + $b + $c + $d + $e, 10, 12, 10, 5, 5));
+
+assertType('bool', await(coroutine(static function () {
+    return true;
+})));
+
+// assertType('bool', await(coroutine(static function () {
+//     return (yield resolve(true));
+// })));

tests/types/parallel.php

@@ -0,0 +1,33 @@
+<?php
+
+use React\Promise\PromiseInterface;
+use function PHPStan\Testing\assertType;
+use function React\Async\await;
+use function React\Async\parallel;
+use function React\Promise\resolve;
+
+assertType('React\Promise\PromiseInterface<array>', parallel([]));
+
+assertType('React\Promise\PromiseInterface<array<bool|float|int>>', parallel([
+    static fn (): PromiseInterface => resolve(true),
+    static fn (): PromiseInterface => resolve(time()),
+    static fn (): PromiseInterface => resolve(microtime(true)),
+]));
+
+assertType('React\Promise\PromiseInterface<array<bool|float|int>>', parallel([
+    static fn (): bool => true,
+    static fn (): int => time(),
+    static fn (): float => microtime(true),
+]));
+
+assertType('array<bool|float|int>', await(parallel([
+    static fn (): PromiseInterface => resolve(true),
+    static fn (): PromiseInterface => resolve(time()),
+    static fn (): PromiseInterface => resolve(microtime(true)),
+])));
+
+assertType('array<bool|float|int>', await(parallel([
+    static fn (): bool => true,
+    static fn (): int => time(),
+    static fn (): float => microtime(true),
+])));