Ability to receive list of requested fields from ResolveInfo (recursively)

src/Type/Definition/ResolveInfo.php

@@ -3,7 +3,10 @@ namespace GraphQL\Type\Definition;
 
 use GraphQL\Language\AST\Field;
 use GraphQL\Language\AST\FragmentDefinition;
+use GraphQL\Language\AST\FragmentSpread;
 use GraphQL\Language\AST\OperationDefinition;
+use GraphQL\Language\AST\Selection;
+use GraphQL\Language\AST\SelectionSet;
 use GraphQL\Schema;
 use GraphQL\Utils;
 
@@ -58,4 +61,64 @@ class ResolveInfo
     {
         Utils::assign($this, $values);
     }
+
+    /**
+     * Helper method that returns names of all fields selected in query for $this->fieldName up to $depth levels
+     *
+     *
+     * query AppHomeRoute{viewer{id,..._0c28183ce}} fragment _0c28183ce on Viewer{id,profile{firstName,id,locations{id}}}
+     * Example:
+     * query MyQuery{
+     * {
+     *   root {
+     *     id,
+     *     nested {
+     *      nested1
+     *      nested2 {
+     *        nested3
+     *      }
+     *     }
+     *   }
+     * }
+     *
+     * Given this ResolveInfo instance is a part of "root" field resolution, and $depth === 1, method will return:
+     * [
+     *     'id' => true,
+     *     'nested' => [
+     *         nested1 => true,
+     *         nested2 => true
+     *     ]
+     * ]
+     *
+     * @param int $depth How many levels to include in output
+     * @return array
+     */
+    public function getFieldSelection($depth = 0)
+    {
+        /** @var Field $fieldAST */
+        $fieldAST = $this->fieldASTs[0];
+        return $this->foldSelectionSet($fieldAST->selectionSet, $depth);
+    }
+
+    private function foldSelectionSet(SelectionSet $selectionSet, $descend)
+    {
+        $fields = [];
+
+        foreach ($selectionSet->selections as $selectionAST) {
+            if ($selectionAST instanceof Field) {
+                $fields[$selectionAST->name->value] = $descend > 0 && !empty($selectionAST->selectionSet)
+                    ? $this->foldSelectionSet($selectionAST->selectionSet, --$descend)
+                    : true;
+            } else if ($selectionAST instanceof FragmentSpread) {
+                $spreadName = $selectionAST->name->value;
+                if (isset($this->fragments[$spreadName])) {
+                    /** @var FragmentDefinition $fragment */
+                    $fragment = $this->fragments[$spreadName];
+                    $fields += $this->foldSelectionSet($fragment->selectionSet, $descend);
+                }
+            }
+        }
+
+        return $fields;
+    }
 }