Compiler should warn on empty style block

[Rich-Harris]

Small thing, but when tidying up components this would be helpful

REPL

<div class='foo'>
  no styles
</div>

<style>
  .foo {
    /* this should be warned about */	
  }
</style>

[PaulBGD]

Maybe it should only warn when built in production? I know in development I'll leave empty blocks to fill in later, having a warning when running in development seems annoying.

[arxpoetica]

I agree w/ @PaulBGD I can't tell you how many times I leave empty CSS selectors on purpose as a reminder to come back—so this has the potential to become noise—

—feature flag?

—production only?

—feature creep?

[Rich-Harris]

Yeah, that makes sense actually. I'll often put selectors in just so I can tweak them in devtools.

[Rich-Harris]

As of 1.54.2 empty selectors are removed in prod mode, but left alone in dev mode