Clean up garbage references for coroutines

Author: clue

src/functions.php

@@ -238,16 +238,19 @@ function coroutine(callable $function, ...$args): PromiseInterface
     $next = function () use ($deferred, $generator, &$next, &$promise) {
         try {
             if (!$generator->valid()) {
+                $next = null;
                 $deferred->resolve($generator->getReturn());
                 return;
             }
         } catch (\Throwable $e) {
+            $next = null;
             $deferred->reject($e);
             return;
         }
 
         $promise = $generator->current();
         if (!$promise instanceof PromiseInterface) {
+            $next = null;
             $deferred->reject(new \UnexpectedValueException(
                 'Expected coroutine to yield ' . PromiseInterface::class . ', but got ' . (is_object($promise) ? get_class($promise) : gettype($promise))
             ));
@@ -260,7 +263,8 @@ function coroutine(callable $function, ...$args): PromiseInterface
         }, function (\Throwable $reason) use ($generator, $next) {
             $generator->throw($reason);
             $next();
-        })->then(null, function (\Throwable $reason) use ($deferred) {
+        })->then(null, function (\Throwable $reason) use ($deferred, &$next) {
+            $next = null;
             $deferred->reject($reason);
         });
     };

tests/CoroutineTest.php

@@ -143,4 +143,99 @@ public function testCoroutineWillCancelAllPendingPromisesWhenFunctionContinuesTo
 
         $promise->then(null, $this->expectCallableOnceWith(new \RuntimeException('Second operation cancelled', 42)));
     }
+
+    public function testCoroutineShouldNotCreateAnyGarbageReferencesWhenGeneratorReturns()
+    {
+        if (class_exists('React\Promise\When')) {
+            $this->markTestSkipped('Not supported on legacy Promise v1 API');
+        }
+
+        gc_collect_cycles();
+        gc_collect_cycles();
+
+        $promise = coroutine(function () {
+            if (false) {
+                yield;
+            }
+            return 42;
+        });
+
+        unset($promise);
+
+        $this->assertEquals(0, gc_collect_cycles());
+    }
+
+    public function testCoroutineShouldNotCreateAnyGarbageReferencesForPromiseRejectedWithExceptionImmediately()
+    {
+        if (class_exists('React\Promise\When')) {
+            $this->markTestSkipped('Not supported on legacy Promise v1 API');
+        }
+
+        gc_collect_cycles();
+
+        $promise = coroutine(function () {
+            yield new Promise(function () {
+                throw new \RuntimeException('Failed', 42);
+            });
+        });
+
+        unset($promise);
+
+        $this->assertEquals(0, gc_collect_cycles());
+    }
+
+    public function testCoroutineShouldNotCreateAnyGarbageReferencesForPromiseRejectedWithExceptionOnCancellation()
+    {
+        if (class_exists('React\Promise\When')) {
+            $this->markTestSkipped('Not supported on legacy Promise v1 API');
+        }
+
+        gc_collect_cycles();
+
+        $promise = coroutine(function () {
+            yield new Promise(function () { }, function () {
+                throw new \RuntimeException('Operation cancelled', 42);
+            });
+        });
+
+        $promise->cancel();
+        unset($promise);
+
+        $this->assertEquals(0, gc_collect_cycles());
+    }
+
+    public function testCoroutineShouldNotCreateAnyGarbageReferencesWhenGeneratorThrowsBeforeFirstYield()
+    {
+        if (class_exists('React\Promise\When')) {
+            $this->markTestSkipped('Not supported on legacy Promise v1 API');
+        }
+
+        gc_collect_cycles();
+
+        $promise = coroutine(function () {
+            throw new \RuntimeException('Failed', 42);
+            yield;
+        });
+
+        unset($promise);
+
+        $this->assertEquals(0, gc_collect_cycles());
+    }
+
+    public function testCoroutineShouldNotCreateAnyGarbageReferencesWhenGeneratorYieldsInvalidValue()
+    {
+        if (class_exists('React\Promise\When')) {
+            $this->markTestSkipped('Not supported on legacy Promise v1 API');
+        }
+
+        gc_collect_cycles();
+
+        $promise = coroutine(function () {
+            yield 42;
+        });
+
+        unset($promise);
+
+        $this->assertEquals(0, gc_collect_cycles());
+    }
 }