inconsistent behaviour of InvalidCast

[SignpostMarv]

issue

• array manually type-hinted to scalar|array|object|resource|null does not flag up MixedAssignment (could go either way on this one)

behaves as expected

• typehinted array correctly flags up InvalidCast
• array manually typed-hinted to scalar|array|object|null does flag up InvalidCast

does not behave as expected

• array assigned to mixed does not flag up InvalidCast
• array manually type-hinted to scalar|array|object|resource|null (aka mixed) does not flag up InvalidCast

repro

• https://psalm.dev/r/fa71008e9a
• using 119687f

<?php
$a = [];

echo (string) $a;

/**
* @var mixed
*/
$b = [];

echo (string) $b;

/**
* @var scalar|array|object|resource|null
*/
$c = [];

echo (string) $c;

/**
* @var scalar|array|object|null
*/
$d = [];

echo (string) $d;

Psalm output (using commit 119687f):

ERROR: InvalidCast - 4:6 - array<empty, empty> cannot be cast to string

INFO: MixedAssignment - 9:1 - Cannot assign $b to a mixed type

ERROR: InvalidCast - 25:6 - array<array-key, mixed>|scalar|object|null cannot be cast to string

[muglug]

It's really just a failure of

/**
* @var array|resource
*/
$c = [];

echo (string) $c;

to emit an error