[New Feature] Extend ArrayShape with ArrayShape

[marartner]

There currently does not seem to be a working way to extend a known array shape with additional keys, other than redefining it entirely. "..." can be used to signal that there may be additional keys, but not which:

I would propose this solution:

https://psalm.dev/r/3afa0bf3db

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/3afa0bf3db

<?php


/**
 *  @psalm-type FooAsArray = array{foo:int, bar:string}
 *  @psalm-type BarAsArray = array{foobar: string, ...FooAsArray}
 */


/** @psalm-return FooAsArray */
function foo(): array {
    return ['foo'=> 1, 'bar' => 'baz'];
}

/** @psalm-return BarAsArray */
function foobar(): array {
    $arr = foo();
    $arr['foobar'] = 'bazbar';
    return $arr;
}

function test(): array {
    $val = foobar();
    /** @psalm-trace $val */
    return $val;
}

// I currently get array{foobar: string, ...<array-key, mixed>}
// I would have expected array{foobar: string, foo:int, bar:string}

Psalm output (using commit 16b24bd):

INFO: Trace - 25:5 - $val: array{foobar: string, ...<array-key, mixed>}