I've run into an issue recently where I've had to move some code from returning a static error to wrapping that error, and noticed that there's not a builtin way to compare errors using the errors.Is function. Would it be possible to add an ErrorIs (or similarly named) Checker implementation that uses errors.Is to assert error similarity?

I can't continue to use ErrorMatches in this case because it doesn't capture the correct meaning of my error check. I want to know that I'm returning a specific kind of error even if it's wrapped or the message is modified.

eg:

// Previously
return package.StaticErrorValue

// Now
return fmt.Errorf("%w: %s", package.StaticErrorValue, reason)

// Tests:
c.Assert(err, ErrorIs, package.StaticErrorValue)

This is coming from go-git/go-git#1097 and https://github.com/go-git/go-git/blob/dcf0639a168c441de6753c6644322e6b619499ae/plumbing/transport/http/common.go#L414-L441 for some context.