Potential risky return of array<int, …>

[nickvergessen]

Sample

<?php

/**
 * @return array<int, int>
 */
function takesAnInt1() {
    return [0, 1, 2];
}

/**
 * @return array<int, int>
 */
function takesAnInt2() {
    $a = [0, 1, 2];
    unset($a[1]);
    return $a;
}

/**
 * @return list<int>
 */
function takesAnInt3() {
    return [0, 1, 2];
}

/**
 * @return list<int>
 */
function takesAnInt4() {
    $a = [0, 1, 2];
    unset($a[1]);
    return $a;
}

Psalm output

Only function 4 warns you:

INFO: [LessSpecificReturnStatement](https://psalm.dev/129) - 32:12 - The type 'array{0: 0, 2: 2}' is more general than the declared return type 'list<int>' for takesAnInt4

INFO: [MoreSpecificReturnType](https://psalm.dev/070) - 27:12 - The declared return type 'list<int>' for takesAnInt4 is more specific than the inferred return type 'array{0: 0, 2: 2}'

But function 2 actually returns string keys as well:

<?php

/**
 * @return array<int, int>
 */
function takesAnInt1() {
    return [0, 1, 2];
}

/**
 * @return array<int, int>
 */
function takesAnInt2() {
    $a = [0, 1, 2];
    unset($a[1]);
    return $a;
}

/**
 * @return list<int>
 */
function takesAnInt3() {
    return [0, 1, 2];
}

/**
 * @return list<int>
 */
function takesAnInt4() {
    $a = [0, 1, 2];
    unset($a[1]);
    return $a;
}


var_dump(json_encode(takesAnInt1()));
var_dump(json_encode(takesAnInt2()));
var_dump(json_encode(takesAnInt3()));
var_dump(json_encode(takesAnInt4()));

string(7) "[0,1,2]"
string(13) "{"0":0,"2":2}"
string(7) "[0,1,2]"
string(13) "{"0":0,"2":2}"

I think we should therefore try to discourage using array<int, …> as API return because it's mostlikely a lie 🍰

[provokateurin]

This should already be prevented by #142