mt_rand assumed to always return the same value

[GKFX]

Bug report

mt_rand returns a random number. The second if statement in the below is therefore not redundant. However PHPStan reports Comparison operation ">" between int<4, max> and 3 is always true..

<?php

if (mt_rand(0,10) > 3) {
    echo 'Fizz';
    if (mt_rand(0,10) > 3) {
        echo 'Buzz';
    }
}
echo "\n";

Code snippet that reproduces the problem

https://phpstan.org/r/43bf48f4-947d-4d96-9fc1-33e25fde3adb

Expected output

No output expected. Arguably, PHPStan should never assume that functions return the same value when called twice with the same arguments, but as this is a standard-library random number function it seems particularly important.

[dktapps]

PHPStan should never assume that functions return the same value when called twice with the same arguments

In some cases the results are entirely deterministic (pure). mt_rand() is not a pure function though.

[GKFX]

PHPStan should never assume that functions return the same value when called twice with the same arguments

In some cases the results are entirely deterministic (pure). mt_rand() is not a pure function though.

Should PHPStan have an annotation for pure and impure functions then, defaulting to impure? It seems to me that assuming functions are not pure by default would be safe, but the current assumption that functions are always pure is false and causes this issue.

[dktapps]

I guess the problem is coming from here: https://github.com/phpstan/phpstan-src/blob/master/resources/functionMetadata.php#L1271

[dktapps]

I guess this will be fixed next time Ondrej updates phpstorm-stubs and regenerates the function metadata.

[phpstan-bot]

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

@@ @@
-5: Comparison operation ">" between int<4, max> and 3 is always true.
+No errors

[ondrejmirtes]

Fixed: phpstan/phpstan-src@d4edc59

[github-actions]

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