Taylor Swift & John Mayer -- These Two, Again?

Taylor Swift and John Mayer showed up at the same place Wednesday night ... eating dinner within eyeshot of each other ... and we know what didn't happen.

We got pics of Swift and Mayer leaving Chateau Marmont in West Hollywood in separate cars ... so there's smoke.

But there's no fire. Our Chateau spies say John and Taylor saw each other but didn't exchange a single word.

They famously dated a few years ago and traded breakup songs about their relationship.