PHP8 "static" return type

[codemasher]

Hi! I just upgraded psr/http-message to ^2.0 and my IDE started yelling at me because my library already requires a minimum of PHP 8.1 and i was already using the new static return type.

src\Psr7\Message.php:45 PhanParamSignatureRealMismatchReturnType Declaration of function withProtocolVersion(string $version) : static should be compatible with function withProtocolVersion(string $version) : \Psr\Http\Message\MessageInterface (method where the return type in the real signature is 'static' cannot override method where the return type in the real signature is '\Psr\Http\Message\MessageInterface') defined in vendor\psr\http-message\src\MessageInterface.php:41

Here, I'm proposing a v3.0 that requires a minimum of PHP 8.0:

• return types have changed from <interface> to static
• mixed types have been added
• several union types (such as array|string) have been added
• additionally I've fixed some grammar and typos in a different branch - you can have these too as separate PR

This update would make the PSR-7 interfaces finally fully typed and I am asking (no I am begging) for a swift review and release ideally before PHP 9 arrives. Thanks!

Edit: I am very well aware that this would break compatibility with v2.0. However, the issue is not the BC break of this PR but the fact that v2.0 was released 3 months ago (2023-04-17) and PHP 8.0 was released almost 3 years ago (2020-11-06), so missing static was not just an oversight, but a collective failure.
So how to proceed? The easiest "fix" for damage control would be to just remove the <interface> return types from the current v2.0 and re-tag it, so that future installs just ignore the return type while maintaining compatibility in both directions. As an alternative, limit v2,0 to PHP ^7.2.

[codemasher]

Thinking about it, this should rather accept mixed to include scalar types, as some implementations are already implemented this way, ignoring the defined type in the docblock.