cmd/go: list: incomplete error "no Go files in"

[alandonovan]

$ cat a.go
package p

import "missing"

$ command go version
go version devel +4da84adc0c Mon Jul 9 19:35:21 2018 +0000 linux/amd64
$ command go list -export -e  a.go
go build missing: no Go files in 
command-line-arguments

I expect the fix is something like this:

--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -185,6 +185,9 @@ func (e *NoGoError) Error() string {
                // to appear at the end of error message.
                return "no non-test Go files in " + e.Package.Dir
        }
+       if e.Package.Dir == "" {
+               return "no directory for package " + e.Package.ImportPath
+       }
        return "no Go files in " + e.Package.Dir
 }

[alandonovan]

Oops, UI glitch created duplicate of #26296.