PHP: Warn on undefined array write

Let’s preface this with an example of a script with typo:

$bc = getBaseConcept();
$bs['key'] = doOtherStuff($bc['key']);
return $bc;

Obviously in the middle line is a typo. It should be $bc instead of $bs. (And yes this was a legit typo of mine just minutes ago before writing this question)

This did not produce a warning.
So my question is: Is there a configuration option that lets this produce a warning?

Specifically: Writing to an array key of a name that was previously undefined.

E_ALL does not seem to help. This should not only generate the warnings for $bar but I want also a warning for $foo.

<?php 
ini_set('error_reporting', E_ALL);
echo ini_get('error_reporting'), "n";
$foo['bar'] = $bar['foo'];

32767

PHP Warning:  Undefined variable $bar in Standard input code on line 4
PHP Warning:  Trying to access array offset on value of type null in Standard input code on line 4