downgrade rule is needed for this, to downgrade constant to previous available constant, since the constant exists since php 8.4

You can see example of it

https://github.com/rectorphp/rector-downgrade-php/blob/abb7e470dba7afed229f82ac0ecea617b9ffc6ec/rules/DowngradePhp84/Rector/FuncCall/DowngradeRoundingModeEnumRector.php#L23

@samsonasik Does this really need a new rector implementation or can't the inverse RenameClassAndConstFetch config be used in config/set/downgrade-php85.php?

PS: I just saw some other rule sets also using "normal" rector rename rules, thus I will do the same.

when downgrading code, that exists in old and removed later, or only exists in future php version, the snippet code generate can be used, eg this example

https://github.com/rectorphp/rector-downgrade-php/blob/main/rules/DowngradePhp72/snippet/isatty_closure.php.inc

Then use inline code parser to cover that

https://github.com/rectorphp/rector-downgrade-php/blob/9a127bbd3442ce88d4953f8b65f18192a4fd517a/rules/DowngradePhp72/Rector/FuncCall/DowngradeStreamIsattyRector.php#L148

@samsonasik Sadly, I can't connect your comment to this PR but I created rectorphp/rector-downgrade-php#304 where we can tackle this discussion and if that solution has issues relating to your example from the previous comment.

Once code downgraded, the code should keep working even on the future php version is met, eg, downgraded from 8.1 to 8.0, when downgraded code opened in php 8.1, it should keep working.

Php is unfortunatelly not semver, so some tweak for this kind of usage seems needed, like if exists check.

I am unsure exactly whether rectorphp/rector-downgrade-php#304 meets these requirements. If it does not, someone else should tackle this topic then, please. At this point in time, I do not want to spend my time on writing code to downgrade PHP code.

It's the same rules, just inverted renames.