% go get -u rsc.io/github/issue
package rsc.io/github/issue
imports 9fans.net/go/acme
imports 9fans.net/go/plan9
imports 9fans.net/go/plan9/client
imports 9fans.net/go/draw
imports 9fans.net/go/draw/drawfcall
imports github.com/google/go-github/github
imports github.com/google/go-querystring/query
imports golang.org/x/oauth2
imports golang.org/x/net/context: /Users/r/src/golang.org/x/net is from https://code.google.com/p/go.net, should be from https://go.googlesource.com/net

The error is the last line, but "should be" doesn't tell me much, as this is a transitive dependency I don't know about. It should say something about what went wrong (vanity import has changed target) or how to fix it (remove stale repo) or .... ?

I found this difficult to understand but easy to fix, implying the error message could be improved.