go/analysis/passes/errorsas works only with the standard package errors. So, I believe it is useless for many projects which use very popular github.com/pkg/errors. Of course, it's possible to alias errors package (for example stderrors) and use it, but I think it's better to update the analyzer.

I see 2 options here:

• hard code github.com/pkg/errors.As. It's the simplest solution but requires an update for every new package
• pass a list of functions via flags. go/analysis/passes/printf uses the similar approach

I think the best solution is to combine these options: use flags with the default functions errors.As and github.com/pkg/errors.As