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UnsupportedReferenceUsage

Emitted when Psalm encounters a reference that it is not currently able to track (for instance a reference to an array offset of an array offset: $foo = &$bar[$baz[0]]). When an unsupported reference is encountered, Psalm will issue this warning and treat the variable as though it wasn't actually a reference.

How to fix

This can sometimes be fixed by using a temporary variable:

<?php

/** @var non-empty-list<int> */
$bar = [1, 2, 3];
/** @var non-empty-list<int> */
$baz = [1, 2, 3];

$foo = &$bar[$baz[0]];

can be turned into

<?php

/** @var non-empty-list<int> */
$bar = [1, 2, 3];
/** @var non-empty-list<int> */
$baz = [1, 2, 3];

$offset = $baz[0];
$foo = &$bar[$offset];