Lit is in dev mode warning message shows up on localhost

[mwawrusch]

Which package(s) are affected?

Lit Core (lit / lit-html / lit-element / reactive-element)

Description

I am indirectly using lit through some other package and always get the 'Lit is running in dev mode' console warning, which is rather distracting.
It would be fantastic if you would NOT show this message when window.location.hostname is localhost.

Reproduction

See above.

Workaround

I have not found a workaround

Is this a regression?

No or unsure. This never worked, or I haven't tried before.

Affected versions

all

Browser/OS/Node environment

all

[sorvell]

Yeah, that can be annoying, but I'm not sure we can say it's always right to not show the warning on localhost.

Here's a workaround. Put this script before loading anything that contains Lit:

<script>
  const c = `Lit is in dev mode. Not recommended for production! See https://lit.dev/msg/dev-mode for more information.`
  window.litIssuedWarnings = new Set();
  litIssuedWarnings.add(c);
</script>

[justinfagnani]

If I were on a team I would want that snippet to issue it's own warning so it's not shipped to production.