declare assert-if-true for filesystem functions

[staabm]

closes phpstan/phpstan#6788

[ondrejmirtes]

Two problems here:

1. chdir($dir) ? 'foo' : 'bar' - in the else branch $dir will be considered ''
2. If you pass non-empty-string to chdir(...), you'll get "always true" error.

Both can be solved with =non-empty-string. See: phpstan/phpstan#8348 + phpstan/phpstan#8351

[ondrejmirtes]

To make sure that = actually fixes these problems, you should have tested the else condition types and also put a test about this in ImpossibleCheckTypeFunctionCallRule (before adding the = everywhere). Please verify this was originally a problem and that it's fixed after the change. I'm sure you can find the previous version in your reflog :) It's e117fce or 49564b7.

[staabm]

good point.

2) PHPStan\Rules\Comparison\ImpossibleCheckTypeFunctionCallRuleTest::testBug6788
Failed asserting that two strings are identical.
--- Expected
+++ Actual
@@ @@
-'
+'13: Call to function chdir() with non-empty-string will always evaluate to true.
+    💡 Because the type is coming from a PHPDoc, you can turn off this check by setting <fg=cyan>treatPhpDocTypesAsCertain: false</> in your <fg=cyan>%configurationFile%</>.
+15: Call to function chdir() with non-falsy-string will always evaluate to true.
+    💡 Because the type is coming from a PHPDoc, you can turn off this check by setting <fg=cyan>treatPhpDocTypesAsCertain: false</> in your <fg=cyan>%configurationFile%</>.
 '