Allow http_response_code() to clear HTTP start-line

[iluuu1994]

Fixes GH-18582
Fixes #81451

[iluuu1994]

@bukka Ping. 🙂

[bukka]

This is a BC break so you will need RFC for this.

[bukka]

I think it would be good to sync this behaviour but there is some risk as it's been there for long - if I understand correctly, this is also the case for FPM - just Apache does not do that.

[bukka]

Basically the implementation can currently rely on the fact that header has got the priority and this might suddenly change the behaviour. You could argue that this is a fix but in this case it's not like the things do not work. It's more about the priority.

[iluuu1994]

IMO, this doesn't seem intentional, and nothing in the documentation ¹ indicates http_response_code() wouldn't work after using header(). I understand this can have BC breaks, which is why I targeted master instead of PHP-8.3. I can shoot a quick e-mail to internals@ if you like.

Footnotes

1. https://www.php.net/manual/en/function.http-response-code.php ↩