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IntMaskComparison

Emitted when a bit set, i.e. a value typed as int-mask<…> or int-mask-of<…>, is compared by value with something other than 0 or the set of all its bits.

<?php

final class Permission
{
    public const READ = 1;
    public const WRITE = 2;
    public const DELETE = 4;
}

/** @param int-mask-of<Permission::*> $permissions */
function canRead(int $permissions): bool
{
    return $permissions === Permission::READ;
}

Why this is bad

$permissions === Permission::READ is only true when READ is the only bit set: canRead(Permission::READ | Permission::WRITE) returns false. Comparing a bit set by value is almost always a mistake for a test of some of its bits.

How to fix

Test the bits you need with &:

<?php

final class Permission
{
    public const READ = 1;
    public const WRITE = 2;
    public const DELETE = 4;
}

/** @param int-mask-of<Permission::*> $permissions */
function canRead(int $permissions): bool
{
    return ($permissions & Permission::READ) === Permission::READ;
}

• ($mask & B) === B: every bit of B is set;
• ($mask & B) !== 0: at least one bit of B is set;
• ($mask & ~B) === 0: no bit outside of B is set, i.e. the mask is a subset of B;
• $mask === 0: no bit is set;
• $mask === ALL, where ALL has every bit of the mask's type: every bit is set.

$mask & B is itself a bit set, of the bits of B, so it may only be compared with 0 or B.

$a & $b may also be compared with $a or $b, as in ($available & $required) === $required.

The check covers ===, !==, ==, !=, <, <=, >, >= and <=> (ordering comparisons only allow 0), match arms, switch cases, and the search value of in_array(), array_search() and array_keys().

When a comparison of the exact set of bits is intended, for instance to tell whether a fixed point was reached, pass the masks to a function taking a plain int that documents that intent.