Prevent infinite recursion when describing template type with default value

Author: ondrejmirtes

src/Type/Generic/TemplateTypeTrait.php

@@ -6,10 +6,12 @@
 use PHPStan\PhpDocParser\Ast\Type\TypeNode;
 use PHPStan\TrinaryLogic;
 use PHPStan\Type\AcceptsResult;
+use PHPStan\Type\ErrorType;
 use PHPStan\Type\IntersectionType;
 use PHPStan\Type\IsSuperTypeOfResult;
 use PHPStan\Type\MixedType;
 use PHPStan\Type\NeverType;
+use PHPStan\Type\RecursionGuard;
 use PHPStan\Type\SubtractableType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
@@ -69,7 +71,13 @@ public function describe(VerbosityLevel $level): string
 			} else {
 				$boundDescription = sprintf(' of %s', $this->bound->describe($level));
 			}
-			$defaultDescription = $this->default !== null ? sprintf(' = %s', $this->default->describe($level)) : '';
+			$defaultDescription = '';
+			if ($this->default !== null) {
+				$recursionGuard = RecursionGuard::runOnObjectIdentity($this->default, fn () => $this->default->describe($level));
+				if (!$recursionGuard instanceof ErrorType) {
+					$defaultDescription .= sprintf(' = %s', $recursionGuard);
+				}
+			}
 			return sprintf(
 				'%s%s%s',
 				$this->name,

src/Type/RecursionGuard.php

@@ -2,6 +2,8 @@
 
 namespace PHPStan\Type;
 
+use function spl_object_hash;
+
 final class RecursionGuard
 {
 
@@ -28,4 +30,24 @@ public static function run(Type $type, callable $callback)
 		}
 	}
 
+	/**
+	 * @template T
+	 * @param callable(): T $callback
+	 * @return T|ErrorType
+	 */
+	public static function runOnObjectIdentity(Type $type, callable $callback)
+	{
+		$key = spl_object_hash($type);
+		if (isset(self::$context[$key])) {
+			return new ErrorType();
+		}
+
+		try {
+			self::$context[$key] = true;
+			return $callback();
+		} finally {
+			unset(self::$context[$key]);
+		}
+	}
+
 }