Fine-grained type checks for Executor

Author: vladar

src/Executor/Executor.php

@@ -415,11 +415,16 @@ private static function resolveField(ExecutionContext $exeContext, ObjectType $p
         if ($mapFn) {
             try {
                 $mapped = call_user_func($mapFn, $sourceValueList, $args, $info);
+                $validType = is_array($mapped) || ($mapped instanceof \Traversable && $mapped instanceof \Countable);
+                $mappedCount = count($mapped);
+                $sourceCount = count($sourceValueList);
 
                 Utils::invariant(
-                    is_array($mapped) && count($mapped) === count($sourceValueList),
-                    "Function `map` of $parentType.$fieldName is expected to return array " .
-                    "with exact same number of items as list being mapped (first argument of `map`)"
+                    $validType && count($mapped) === count($sourceValueList),
+                    "Function `map` of $parentType.$fieldName is expected to return array or " .
+                    "countable traversable with exact same number of items as list being mapped. ".
+                    "Got '%s' with count '$mappedCount' against '$sourceCount' expected.",
+                    Utils::getVariableType($mapped)
                 );
 
             } catch (\Exception $error) {
@@ -682,7 +687,8 @@ private static function completeValue(ExecutionContext $exeContext, Type $return
 
         // Collect sub-fields to execute to complete this value.
         $subFieldASTs = self::collectSubFields($exeContext, $objectType, $fieldASTs);
-        return self::executeFields($exeContext, $objectType, [$result], $subFieldASTs)[0];
+        $executed = self::executeFields($exeContext, $objectType, [$result], $subFieldASTs);
+        return isset($executed[0]) ? $executed[0] : null;
     }
 
     /**

src/Utils.php

@@ -86,6 +86,24 @@ public static function map($traversable, callable $fn)
         return $map;
     }
 
+    /**
+     * @param $traversable
+     * @param callable $fn
+     * @return array
+     * @throws \Exception
+     */
+    public static function mapKeyValue($traversable, callable $fn)
+    {
+        self::invariant(is_array($traversable) || $traversable instanceof \Traversable, __METHOD__ . ' expects array or Traversable');
+
+        $map = [];
+        foreach ($traversable as $key => $value) {
+            list($newKey, $newValue) = $fn($value, $key);
+            $map[$newKey] = $newValue;
+        }
+        return $map;
+    }
+
     /**
      * @param $traversable
      * @param callable $keyFn function($value, $key) => $newKey
@@ -106,6 +124,19 @@ public static function keyMap($traversable, callable $keyFn)
         return $map;
     }
 
+    /**
+     * @param $traversable
+     * @param callable $fn
+     */
+    public static function each($traversable, callable $fn)
+    {
+        self::invariant(is_array($traversable) || $traversable instanceof \Traversable, __METHOD__ . ' expects array or Traversable');
+
+        foreach ($traversable as $key => $item) {
+            $fn($item, $key);
+        }
+    }
+
     /**
      * Splits original traversable to several arrays with keys equal to $keyFn return
      *