Hi,

since this is guarded by an extension that doesn't even exist yet, no code is broken, is there?

I also don't expect this to be enabled in the future without coinciding with an intentional action by the developers - enabling this extension or switching to a future language edition that has this enabled by default (should that ever exist). Is it not sufficient if they are _then_ bothered with this change?

(That said, we could say that a unparenthized type annotation on a pattern synonym is simply confusing, and thus use a warning to nudge the developers to add the parentheses now.)

So not opposed to an early warning, I just don't think it's strictly necessary for this change.

Cheers,
Joachim