Bug report

In PHP, if you call a non-variadic function/method using named arguments, but use an argument name that doesn't exist, you'll get a fatal "Unknown named parameter" error. Normally, PHPStan will detect this issue and report an argument.unknown error.

However, if the function is non-variadic but it uses func_get_args() inside, PHPStan will treat it as a variadic function. Because PHPStan thinks its a variadic function, it skips the named argument check since variadic functions can take any named argument without throwing an error.

This leads to a scenario where there is a detectable fatal error, but PHPStan is not catching it.

// THIS WORKS

function non_variadic(string $name, ?string $greeting = null): void {
    var_dump($name);
}

// PHPStan correctly detects the error ('greetings' vs 'greeting').
non_variadic('my name', greetings: 'my greeting');

// THIS ALSO WORKS

// Explicitly defined with variadic arguments.
function explicit_variadic(string $name, ?string $greeting = null, string ...$args): void {
    var_dump($name);
}

// PHPStan correctly doesn't report anything since the function accepts variadic
// arguments and this will not cause an error.
explicit_variadic('my name', greetings: 'my greeting');

// ISSUE HERE

// PHPStan treats as variadic due to `func_get_args()`.
function implicit_variadic(string $name, ?string $greeting = null): void {
    var_dump(func_get_args());
}

// This will cause a PHP fatal error.
// PHPStan should detect argument.unknown error, but it doesn't.
implicit_variadic('my name', greetings: 'my greeting');

In the code above, the implicit_variadic() function is not a real variadic function, so calling it with invalid named arguments will cause a PHP error. Since it is not defined as a variadic function, the argument names should still be checked by PHPStan to catch this error.

Code snippet that reproduces the problem

https://phpstan.org/r/2b0553a1-cbd3-408c-a073-34f8ad6f7e4f

Expected output

PHPStan should detect an issue with the code but doesn't. PHPStan should not skip named argument validation for implicit variadic functions.

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