Bug report

Consider this code:

function check_identifier( string $id ): bool {
	if ( 1 !== preg_match( '/^[a-z]+$/s', $id ) ) {
		return false;
	}
	PHPStan\dumpType( $id );
	return true;
}

The dumped type for $id should be non-empty-lowercase-string (or lowercase-string&non-empty-string). Instead, it is just non-empty-string.

Furthermore, after running the $id through strtolower(), the type then becomes lowercase-string&non-empty-string but this fails the PHPStan\Testing\assertType() check against non-empty-lowercase-string.

Code snippet that reproduces the problem

https://phpstan.org/r/796e8a72-6465-4676-819e-e8fbfe2af89f

Expected output

The type should be narrowed from string to non-empty-lowercase-string.

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YES! Can't get enough typing.