Another "Cannot unset offset on array" false positive

[alexpott]

Bug report

Code snippet that reproduces the problem

/**
 * Reads configuration data from the storage.
 * @return array|bool
 */
function readThing() {
  return ['module' => ['test' => 0]];
}

$extensions = readThing();
$extensions['theme']['test_basetheme'] = 0;
// This is the important part of the test. Themes are ordered alphabetically
// in core.extension so this will come before it's base theme.
$extensions['theme']['test_subtheme'] = 0;
$extensions['theme']['test_subsubtheme'] = 0;
unset($extensions['theme']['test_basetheme']);
unset($extensions['theme']['test_subsubtheme']);
unset($extensions['theme']['test_subtheme']);

Expected: No errors
Results in:

Cannot unset offset 'test_basetheme' on array{test_subtheme: 0, test_subsubtheme: 0}.

https://phpstan.org/r/33cd311d-fd19-430a-b3f5-945174682f2a

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[alexpott]

Might be related to #4565

[alexpott]

Note that the @return array|bool is what is important here. If this is only @return array the code passes. Yes you could argue that we should be checking the return type of readThing(); before using it but this is from a test and the test knows that this is going to be an array.

[alexpott]

Also note that:

• adding $extensions = readThing(); just before the unsets also results in no errors.
• removing unset($extensions['theme']['test_basetheme']); results in no errors.

[phpstan-bot]

@alexpott After the latest push in 1.8.x, PHPStan now reports different result with your code snippet:

@@ @@
-17: Cannot unset offset 'test_basetheme' on array{test_subtheme: 0, test_subsubtheme: 0}.
+No errors

[github-actions]

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