composer.json

{
    "name": "firehed/psalm-repro",
    "require-dev": {
        "vimeo/psalm": "dev-master"
    },
    "authors": [
        {
            "name": "Eric Stern",
            "email": "[email protected]"
        }
    ],
    "autoload": {
      "psr-4": {
        "Foo\\": "src"
      }
    },
    "require": {}
}

list.php

<?php
return [
    1,
    2,
    3,
];

src_Bar.php

<?php

namespace Foo;

class Bar
{
    public function baz()
    {
        $file = 'list.php';
        if (!file_exists($file)) {
            throw new \RuntimeException();
        }
        $data = include $file;
        return $data;
    }
}

Note: src_Bar.php should be src/Bar.php but Gists don't support directories.