go/build: change the wording of NoGoError and comment it better

Out of context, it can be very confusing because there can be lots of Go
files in the directory, but the error message says there aren't.

R=golang-dev, dsymonds, rsc
CC=golang-dev
https://golang.org/cl/12823043

diff --git a/src/pkg/go/build/build.go b/src/pkg/go/build/build.go
index 563e7fe21b8a9ce49aafb5756425e9aba7ee6ca9..ecea22456e25694a43e53dded934bcd434eafcba 100644 (file)
--- a/src/pkg/go/build/build.go
+++ b/src/pkg/go/build/build.go
@@ -395,13 +395,14 @@ func (ctxt *Context) ImportDir(dir string, mode ImportMode) (*Package, error) {
 }
 
 // NoGoError is the error used by Import to describe a directory
-// containing no Go source files.
+// containing no buildable Go source files. (It may still contain
+// test files, files hidden by build tags, and so on.)
 type NoGoError struct {
        Dir string
 }
 
 func (e *NoGoError) Error() string {
-       return "no Go source files in " + e.Dir
+       return "no buildable Go source files in " + e.Dir
 }
 
 // Import returns details about the Go package named by the import path,