Variable type is discarded after use as by-reference arg #1953
Description
function foo(string &$s) : void {
$i = "goodbye";
}
$a = "hello";
foo($a);
echo $a->bar();Expected: Cannot call method bar() on string.
Actual: No issue
https://phpstan.org/r/dc07834e-c39e-4ad4-8034-91c22c38cdda
Suggestion: assume the type does not change inside the called function, and add checks when it does e.g.
function foo(string &$s) : void {
$s = 5;
}would result in
Variable $s is limited to values of type string because it is passed by reference, int found
To work around this, the developer would add a @param-out annotation
/**
* @param-out int $s
*/
function foo(string &$s) : void {
$s = 5;
}Implementation
At every return statement (including the implicit return at the bottom) the current param types would be checked against the expected byref param types, taking into account any @param-out overrides.
So this would be a bug:
/**
* @param-out int $s
*/
function foo(string &$s) : void {
if (rand(0, 1)) {
return;
}
$s = 5;
}