Avoid garbage reference by hiding resolver from call stack on PHP 7+

src/Promise.php

@@ -16,7 +16,12 @@ public function __construct(callable $resolver, callable $canceller = null)
     {
         $this->canceller = $canceller;
 
-        $this->call($resolver);
+        // Explicitly overwrite arguments with null values before invoking
+        // resolver function. This ensure that these arguments do not show up
+        // in the stack trace in PHP 7+ only.
+        $cb = $resolver;
+        $resolver = $canceller = null;
+        $this->call($cb);
     }
 
     public function then(callable $onFulfilled = null, callable $onRejected = null, callable $onProgress = null)

tests/PromiseTest.php

@@ -135,6 +135,24 @@ public function shouldRejectWithoutCreatingGarbageCyclesIfCancellerWithReference
         $this->assertSame(0, gc_collect_cycles());
     }
 
+    /**
+     * @test
+     * @requires PHP 7
+     * @see self::shouldRejectWithoutCreatingGarbageCyclesIfCancellerWithReferenceThrowsException
+     */
+    public function shouldRejectWithoutCreatingGarbageCyclesIfResolverWithReferenceThrowsException()
+    {
+        gc_collect_cycles();
+
+        $promise = new Promise(function () use (&$promise) {
+            throw new \Exception('foo');
+        });
+
+        unset($promise);
+
+        $this->assertSame(0, gc_collect_cycles());
+    }
+
     /** @test */
     public function shouldIgnoreNotifyAfterReject()
     {