Improvements to printing block strings

ref: graphql/graphql-js#f9e67c403a4667372684ee8c3e82e1f0ba27031b

src/Language/Printer.php

@@ -140,7 +140,7 @@ class Printer
                 },
                 NodeKind::STRING => function(StringValueNode $node) {
                     if ($node->block) {
-                       return "\"\"\"\n" . str_replace('"""', '\\"""', $node->value) . "\n\"\"\"";
+                       return $this->printBlockString($node->value);
                     }
                     return json_encode($node->value);
                 },
@@ -310,4 +310,15 @@ class Printer
             )
             : '';
     }
+
+    /**
+     * Print a block string in the indented block form by adding a leading and
+     * trailing blank line. However, if a block string starts with whitespace and is
+     * a single-line, adding a leading blank line would strip that whitespace.
+     */
+    private function printBlockString($value) {
+        return ($value[0] === ' ' || $value[0] === "\t") && strpos($value, "\n") === false
+            ? '"""' . str_replace('"""', '\\"""', $value) . '"""'
+            : $this->indent("\"\"\"\n" . str_replace('"""', '\\"""', $value)) . "\n\"\"\"";
+    }
 }

tests/Language/PrinterTest.php

@@ -92,6 +92,46 @@ class PrinterTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals($expected, Printer::doPrint($mutationAstWithArtifacts));
     }
 
+    /**
+     * @it correctly prints single-line block strings with leading space
+     */
+    public function testCorrectlyPrintsSingleLineBlockStringsWithLeadingSpace()
+    {
+        $mutationAstWithArtifacts = Parser::parse(
+          '{ field(arg: """    space-led value""") }'
+        );
+        $expected = '{
+  field(arg: """    space-led value""")
+}
+';
+    $this->assertEquals($expected, Printer::doPrint($mutationAstWithArtifacts));
+    }
+        
+    /**
+     * @it correctly prints block strings with a first line indentation
+     */
+    public function testCorrectlyPrintsBlockStringsWithAFirstLineIndentation()
+    {
+        $mutationAstWithArtifacts = Parser::parse(
+            '{
+  field(arg: """
+        first
+      line
+    indentation
+  """)
+}'
+          );
+          $expected = '{
+  field(arg: """
+        first
+      line
+    indentation
+  """)
+}
+';
+      $this->assertEquals($expected, Printer::doPrint($mutationAstWithArtifacts));
+    }
+
     /**
      * @it prints kitchen sink
      */