Add concatAST utility function (#930)

CHANGELOG.md

@@ -27,6 +27,7 @@ You can find and compare releases at the [GitHub release page](https://github.co
 - Add tests for errors that occur when undeclared fields are passed in input
 - Warn about orphaned object types
 - Expose structured enumeration of directive locations
+- Add `AST::concatAST()` utility
 - Allow lazy input object fields
 
 ### Optimized

src/Utils/AST.php

@@ -9,6 +9,7 @@
 use GraphQL\Error\Error;
 use GraphQL\Error\InvariantViolation;
 use GraphQL\Language\AST\BooleanValueNode;
+use GraphQL\Language\AST\DefinitionNode;
 use GraphQL\Language\AST\DocumentNode;
 use GraphQL\Language\AST\EnumValueNode;
 use GraphQL\Language\AST\FloatValueNode;
@@ -43,6 +44,7 @@
 use Traversable;
 
 use function array_key_exists;
+use function array_push;
 use function count;
 use function is_array;
 use function is_bool;
@@ -608,4 +610,24 @@ public static function getOperationAST(DocumentNode $document, ?string $operatio
 
         return $operation;
     }
+
+    /**
+     * Provided a collection of ASTs, presumably each from different files,
+     * concatenate the ASTs together into batched AST, useful for validating many
+     * GraphQL source files which together represent one conceptual application.
+     *
+     * @param array<DocumentNode> $documents
+     *
+     * @api
+     */
+    public static function concatAST(array $documents): DocumentNode
+    {
+        /** @var array<DefinitionNode> $definitions */
+        $definitions = [];
+        foreach ($documents as $document) {
+            array_push($definitions, ...$document->definitions);
+        }
+
+        return new DocumentNode(['definitions' => new NodeList($definitions)]);
+    }
 }

tests/Utils/ConcatASTTest.php

@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Tests\Utils;
+
+use GraphQL\Language\Parser;
+use GraphQL\Language\Printer;
+use GraphQL\Utils\AST;
+use PHPUnit\Framework\TestCase;
+
+class ConcatASTTest extends TestCase
+{
+    /**
+     * @see it('concatenates two ASTs together'
+     */
+    public function testConcatenatesTwoAstsTogether(): void
+    {
+        $sourceA = '
+          { a, b, ...Frag }
+        ';
+
+        $sourceB = '
+          fragment Frag on T {
+            c
+          }
+        ';
+
+        $astA = Parser::parse($sourceA);
+        $astB = Parser::parse($sourceB);
+        $astC = AST::concatAST([$astA, $astB]);
+
+        self::assertEquals(
+            <<<'GRAPHQL'
+              {
+                a
+                b
+                ...Frag
+              }
+
+              fragment Frag on T {
+                c
+              }
+
+              GRAPHQL,
+            Printer::doPrint($astC)
+        );
+    }
+}