When I clicked on the link to codebases relying on the specific error string, I was expecting to see random side projects. Wasn't expecting to see Grafana and Caddy on the list.

To be fair to those projects, the type was introduced only three years ago:

https://github.com/golang/go/pull/49359/files

Before that, doing a string compare was basically the only way to detect that specific error. That was definitely an omission on the part of the original authors of the stdlib code; I don't it should be classified as "Hyrum's Law".

Hey Anders; Francis notified us of this today. I didn't realize a proper type had been created. We'll update our code.

Never underestimate the mediocrity of known large codebases, lol.

(just kidding, they're not mediocre, but they're not infallible or perfect either)