Bug: AddArrowFunctionParamArrayWhereDimFetchRector incorrectly adds 'array' type to string parameter

[antoniovj1]

Bug Report

Subject	Details
Rector version	2.1.4

The AddArrowFunctionParamArrayWhereDimFetchRector rule incorrectly adds an array type hint to a parameter that is actually a string. This happens when a string offset is accessed (e.g., $string[0]) inside an array_map callback.

The rule seems to assume that any variable with a dimension fetch ($var[key]) must be an array, but this is also valid syntax for accessing characters in a string. This incorrect assumption introduces a TypeError at runtime.

Minimal PHP Code Causing Issue

Here is a minimal reproducible example on the playground:

https://getrector.com/demo/eed23d9a-8ac2-4c49-98e7-29700e8c2dc3

<?php

$username = 'john.doe';

$initials = implode(
    '',
    array_map(
        static fn ($name): string => strtoupper((string) $name[0]),
        explode('.', $username),
    ),
);

Rector changes it to:

PHP

<?php

$username = 'john.doe';

$initials = implode(
    '',
    array_map(
        static fn (array $name): string => strtoupper((string) $name[0]),
        explode('.', $username),
    ),
);

Expected Behaviour

Rector should not type as array.

It should correctly identify that the $name parameter in the array_map callback is a string, as it iterates over the array of strings returned by explode(). The string offset access $name[0] is valid for strings, and the parameter should not be incorrectly typed as array.

Thanks!

[github-actions]

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