Add support for PHP 7.4 arrow functions

[jrfnl]

PHP 7.4 introduces arrow functions. It would be great if this library would add support for these.

// Currently throwing false positives for undefined variables $a x 2, $b x 2, $c x 1.
$fn = fn($a, $b, $c) => $a + $b; // Unused $c (false negative).

function foo() {
    $a = 120;

	// Currently throwing false positive for undefined variable $b x 2.
    $fn1 = fn($b) => $a + $b;

	// Currently throwing false positive for undefined variable $b.
    $fn2 = fn($b) => $a; // Unused $b (false negative).

	// Currently throwing false positive for undefined variable $b x 2, $c x 1.
    $fn3 = fn($b) => $b + $c; // Undefined $c (false negative). Unused variable $fn3 (correctly thrown).
    
    var_dump( $fn1(10) );
    var_dump( $fn2(10) );
}

Note: PHPCS itself doesn't properly support arrow functions until PHPCS 3.5.5 (not yet released).
If continued support for older PHPCS versions is desired, you may want to look at the PHPCSUtils FunctionDeclarations::isArrowFunction() and FunctionDeclarations::getArrowFunctionOpenClose() methods.

Refs:

• https://wiki.php.net/rfc/arrow_functions_v2
• PHP 7.4: arrow functions squizlabs/PHP_CodeSniffer#2523

[sirbrillig]

Yes. Thanks for bringing this up. I'm very excited about PHP 7.4 but I hadn't started looking into it yet. No time like the present.

[speicus]

Subscribing for updates. Really hoping for a fix, unfortunately having to add // phpcs:ignore VariableAnalysis.CodeAnalysis.VariableAnalysis.UndefinedVariable to each arrow function really discourages us from using them more widely.

[gertjankrol]

+1