Templated types defined as union types causing unexpected InvalidArgument errors

[jaikdean]

This issue seems to have been introduced in 4.24.0.

https://psalm.dev/r/dbb9cbe3c0

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/dbb9cbe3c0

<?php

/**
 * @template T of int|numeric-string
 */
class Foo {}

function bar(Foo $foo): void {
    echo $foo::class;
}

/** @var Foo<numeric-string> $foo */
$foo = new Foo();

bar($foo);

Psalm output (using commit 8c716f8):

ERROR: InvalidArgument - 15:5 - Argument 1 of bar expects Foo<int|numeric-string>, Foo<numeric-string> provided

[jaikdean]

I suspect it was introduced by #8069

[AndrolGenhald]

This is actually correct, and was previously a false-negative. If you don't mark the template as covariant you can run into this type of bug (which is a huge problem if, for example, $foo is a reference to another object's property marked as Foo<numeric-string> which suddenly becomes Foo<int>).

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/8ea443e090

<?php

/**
 * @template-covariant T of int|numeric-string
 */
class Foo {}

function bar(Foo $foo): void {
    echo $foo::class;
}

/** @var Foo<numeric-string> $foo */
$foo = new Foo();

bar($foo);

Psalm output (using commit 8c716f8):

No issues!

[jaikdean]

Very interesting, thanks @AndrolGenhald.