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Error Identifier: interface.duplicate

Every error reported by PHPStan has an error identifier. Here’s a list of all error identifiers. In PHPStan Pro you can see the error identifier next to each error and filter errors by their identifiers.

Code example #

<?php declare(strict_types = 1);

// In file: src/Contracts/Logger.php
namespace App\Contracts;

interface Logger
{
	public function log(string $message): void;
}

<?php declare(strict_types = 1);

// In file: src/Legacy/Logger.php
namespace App\Contracts;

interface Logger
{
	public function log(string $message): void;
}

Why is it reported? #

The same interface is declared in multiple files within the analysed codebase. PHP does not allow two interfaces with the same fully-qualified name. When the autoloader loads one of them, the other becomes unreachable, and if both files are included, a fatal error occurs.

In the example above, App\Contracts\Logger is defined in two different files.

How to fix it #

Remove the duplicate declaration and keep only one definition of the interface:

-// Delete or rename the duplicate file src/Legacy/Logger.php

If both interfaces are needed, give them different names or place them in different namespaces:

 <?php declare(strict_types = 1);
 
-namespace App\Contracts;
+namespace App\Legacy;

-interface Logger
+interface LegacyLogger
 {
 	public function log(string $message): void;
 }

How to ignore this error #

You can use the identifier interface.duplicate to ignore this error using a comment:

// @phpstan-ignore interface.duplicate
codeThatProducesTheError();

You can also use only the identifier key to ignore all errors of the same type in your configuration file in the ignoreErrors parameter:

parameters:
	ignoreErrors:
		-
			identifier: interface.duplicate

Rules that report this error #

• PHPStan\Rules\Classes\DuplicateClassDeclarationRule [1]

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