Provide a path with a correct list index to resolveType callback of the union and interface types (fixes #396)

src/Executor/ReferenceExecutor.php

@@ -949,6 +949,7 @@ class ReferenceExecutor implements ExecutorImplementation
         foreach ($result as $item) {
             $fieldPath     = $path;
             $fieldPath[]   = $i++;
+            $info->path    = $fieldPath;
             $completedItem = $this->completeValueCatchingError($itemType, $fieldNodes, $info, $fieldPath, $item);
             if (! $containsPromise && $this->getPromise($completedItem)) {
                 $containsPromise = true;

src/Experimental/Executor/CoroutineExecutor.php

@@ -620,8 +620,9 @@ class CoroutineExecutor implements Runtime, ExecutorImplementation
             foreach ($value as $itemValue) {
                 ++$index;
 
-                $itemPath   = $path;
+                $itemPath               = $path;
-                $itemPath[] = $index; // !!! use arrays COW semantics
+                $itemPath[]             = $index; // !!! use arrays COW semantics
+                $ctx->resolveInfo->path = $itemPath;
 
                 try {
                     if (! $this->completeValueFast($ctx, $itemType, $itemValue, $itemPath, $itemReturnValue)) {

tests/Regression/Issue396Test.php

@@ -0,0 +1,156 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Tests\Regression;
+
+use GraphQL\GraphQL;
+use GraphQL\Type\Definition\InterfaceType;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\ResolveInfo;
+use GraphQL\Type\Definition\Type;
+use GraphQL\Type\Definition\UnionType;
+use GraphQL\Type\Schema;
+use PHPUnit\Framework\TestCase;
+use function stristr;
+
+/**
+ * @see https://github.com/webonyx/graphql-php/issues/396
+ */
+class Issue396Test extends TestCase
+{
+    public function testUnionResolveType()
+    {
+        $a = new ObjectType(['name' => 'A', 'fields' => ['name' => Type::string()]]);
+        $b = new ObjectType(['name' => 'B', 'fields' => ['name' => Type::string()]]);
+        $c = new ObjectType(['name' => 'C', 'fields' => ['name' => Type::string()]]);
+
+        $log = [];
+
+        $unionResult = new UnionType([
+            'name' => 'UnionResult',
+            'types' => [$a, $b, $c],
+            'resolveType' => static function ($result, $root, ResolveInfo $info) use ($a, $b, $c, &$log) : Type {
+                $log[] = [$result, $info->path];
+                if (stristr($result['name'], 'A')) {
+                    return $a;
+                }
+                if (stristr($result['name'], 'B')) {
+                    return $b;
+                }
+                if (stristr($result['name'], 'C')) {
+                    return $c;
+                }
+            },
+        ]);
+
+        $exampleType = new ObjectType([
+            'name' => 'Example',
+            'fields' => [
+                'field' => [
+                    'type' => Type::nonNull(Type::listOf(Type::nonNull($unionResult))),
+                    'resolve' => static function () : array {
+                        return [
+                            ['name' => 'A 1'],
+                            ['name' => 'B 2'],
+                            ['name' => 'C 3'],
+                        ];
+                    },
+                ],
+            ],
+        ]);
+
+        $schema = new Schema(['query' => $exampleType]);
+
+        $query = '
+            query {
+                field {
+                    ... on A {
+                        name
+                    }
+                    ... on B {
+                        name
+                    }
+                    ... on C {
+                        name
+                    }
+                }
+            }
+        ';
+
+        GraphQL::executeQuery($schema, $query);
+
+        $expected = [
+            [['name' => 'A 1'], ['field', 0]],
+            [['name' => 'B 2'], ['field', 1]],
+            [['name' => 'C 3'], ['field', 2]],
+        ];
+        self::assertEquals($expected, $log);
+    }
+
+    public function testInterfaceResolveType()
+    {
+        $log = [];
+
+        $interfaceResult = new InterfaceType([
+            'name' => 'InterfaceResult',
+            'fields' => [
+                'name' => Type::string(),
+            ],
+            'resolveType' => static function ($result, $root, ResolveInfo $info) use (&$a, &$b, &$c, &$log) : Type {
+                $log[] = [$result, $info->path];
+                if (stristr($result['name'], 'A')) {
+                    return $a;
+                }
+                if (stristr($result['name'], 'B')) {
+                    return $b;
+                }
+                if (stristr($result['name'], 'C')) {
+                    return $c;
+                }
+            },
+        ]);
+
+        $a = new ObjectType(['name' => 'A', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
+        $b = new ObjectType(['name' => 'B', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
+        $c = new ObjectType(['name' => 'C', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
+
+        $exampleType = new ObjectType([
+            'name' => 'Example',
+            'fields' => [
+                'field' => [
+                    'type' => Type::nonNull(Type::listOf(Type::nonNull($interfaceResult))),
+                    'resolve' => static function () : array {
+                        return [
+                            ['name' => 'A 1'],
+                            ['name' => 'B 2'],
+                            ['name' => 'C 3'],
+                        ];
+                    },
+                ],
+            ],
+        ]);
+
+        $schema = new Schema([
+            'query' => $exampleType,
+            'types' => [$a, $b, $c],
+        ]);
+
+        $query = '
+            query {
+                field {
+                    name
+                }
+            }
+        ';
+
+        GraphQL::executeQuery($schema, $query);
+
+        $expected = [
+            [['name' => 'A 1'], ['field', 0]],
+            [['name' => 'B 2'], ['field', 1]],
+            [['name' => 'C 3'], ['field', 2]],
+        ];
+        self::assertEquals($expected, $log);
+    }
+}