feat: allow multiline arrow functions

[xepozz]

I've played with the lexer and complete the multiline arrow functions.

Implementation is quite simple:

• old way with no {}
• new way with {}, like the regular functions

Key points:

• Returning from the arrow function means returning the result to the function point, not to the parent constructions
• It should work the same way, because the old way to use arrow function used emulated RETURN ast node, which is similar to fn() => return, but it's not acceptable by the lexer. I didn't change that, just added a new way to allow multiline statements.

The last think I don't know how to solve is #7900 issue:

try {
    assert((fn(): never => {
        return 42;
    }) && false);
} catch (\Error $e) {
    echo $e->getMessage(), "\n";
}

Isn't handled by the catch, 'cause it leads to a Fatal error.
Although, it looks correct because there is no RETURN token added implicitly

@iluuu1994 I remember you've preparing long arrow functions and match expressions, but I think it can be added separately, so I can reference your RFC if I go to there. What do you think?

[iluuu1994]

Hi @xepozz. There was already an RFC for this that was declined. https://wiki.php.net/rfc/auto-capture-closure Edit: Sorry @Xepo for the wrong ping.

[xepozz]

Heh, thanks for the answer.

That change seems very useful for me, I'll go through RFC anyway. There are no big deal between one-line and multiline functions for the php core, but the impact is significant for userland.

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The another implementation looks a bit different, including Zend optimizer changes, are they necessary?

[iluuu1994]

Yes. They avoid unnecessary variable capturing. I think you won't have a big chance of success submitting the RFC with no changes.