B.php

<?php

class T {}

abstract class A {
    /** @param array<int, T> $t */
    abstract protected function f(array $t): void;
}

class B extends A
{
    /**
     * @param array<int, T> $t
     */
    public function f(array $t): void
    {
    }
}

composer.json

{
    "name": "vincentlanglet/twig-cs-fixer",
    "require-dev": {
        "vimeo/psalm": "dev-master"
    },
    "autoload": {
        "psr-4": {
            "": "."
        }
    }
}

psalm.xml

<?xml version="1.0" encoding="UTF-8"?>
<psalm xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns="https://getpsalm.org/schema/config"
       xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
       phpVersion="8.0"
>
    <projectFiles>
        <file name="B.php" />
        <ignoreFiles>
            <directory name="vendor" />
        </ignoreFiles>
    </projectFiles>
</psalm>