\settype() is not handled properly

[kiler129]

Bug report

PHPStan seems to be blind to typecasts done via \settype() and suggests that variable type didn't change.

Code snippet that reproduces the problem

<?php declare(strict_types = 1);

/**
 * @return string|int|float|null Based on the specified casting
 */
function castTo(string $value, string $castTo)
{
	$newValue = $value;
	settype($newValue, $castTo);
	
	return $newValue;
}

https://phpstan.org/r/20eca26c-c9a6-458e-ab03-23cf27cd57eb

Expected output

I think if type cannot be inferred (like in the example above) the return type should be simply trusted. Additional think which will be even better is suggesting the user to add declaration before settype(), e.g.: /** @var string|int|float|bool|null $newValue */

[ondrejmirtes]

This is a matter of writing a TypeSpecifyingExtension: https://phpstan.org/developing-extensions/type-specifying-extensions

PHPStan already contains plenty of those. Feel free to send a PR :)

[phpstan-bot]

@kiler129 PHPStan now reports different result with your code snippet:

@@ @@
+PHP 7.4 – 8.0 (1 error)
+==========
+
+6: Function castTo() has no return typehint specified.
+
+PHP 7.3 (3 errors)
+==========
+
 6: Function castTo() never returns float so it can be removed from the return typehint.
 6: Function castTo() never returns int so it can be removed from the return typehint.
-6: Function castTo() never returns null so it can be removed from the return typehint.
+6: Function castTo() never returns null so it can be removed from the return typehint.
+
+PHP 7.1 – 7.2 (1 error)
+==========
+
+6: Function castTo() has no return typehint specified.

Full report

PHP 7.4 – 8.0 (1 error)

Line	Error
6	Function castTo() has no return typehint specified.

PHP 7.3 (3 errors)

Line	Error
6	Function castTo() has no return typehint specified.
6	Function castTo() has no return typehint specified.
6	Function castTo() has no return typehint specified.

PHP 7.1 – 7.2 (1 error)

Line	Error
6	Function castTo() never returns null so it can be removed from the return typehint.

[phpstan-bot]

@kiler129 After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-6: Function castTo() never returns float so it can be removed from the return typehint.
-6: Function castTo() never returns int so it can be removed from the return typehint.
-6: Function castTo() never returns null so it can be removed from the return typehint.
+6: Function castTo() never returns float so it can be removed from the return type.
+6: Function castTo() never returns int so it can be removed from the return type.
+6: Function castTo() never returns null so it can be removed from the return type.

Full report

Line	Error
6	Function castTo() never returns float so it can be removed from the return type.
6	Function castTo() never returns int so it can be removed from the return type.
6	Function castTo() never returns null so it can be removed from the return type.