cmd/go: suppress extraneous newlines in list

Before:
$ go list -f '{{range .Deps}}{{println $.Name .}}{{end}}' math time
math runtime
math unsafe

time errors
time runtime
time sync
time sync/atomic
time syscall
time unsafe

$

After:
$ go list -f '{{range .Deps}}{{println $.Name .}}{{end}}' math time
math runtime
math unsafe
time errors
time runtime
time sync
time sync/atomic
time syscall
time unsafe
$

R=minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7130052

diff --git a/src/cmd/go/list.go b/src/cmd/go/list.go
index 391c47e94a1bee9e9cc86c631b6a7e849af61a55..25a6f45c1bf4026edeedfff9a29f9ca7706baffe 100644 (file)
--- a/src/cmd/go/list.go
+++ b/src/cmd/go/list.go
@@ -99,7 +99,7 @@ var listJson = cmdList.Flag.Bool("json", false, "")
 var nl = []byte{'\n'}
 
 func runList(cmd *Command, args []string) {
-       out := newCountingWriter(os.Stdout)
+       out := newTrackingWriter(os.Stdout)
        defer out.w.Flush()
 
        var do func(*Package)
@@ -119,13 +119,12 @@ func runList(cmd *Command, args []string) {
                        fatalf("%s", err)
                }
                do = func(p *Package) {
-                       out.Reset()
                        if err := tmpl.Execute(out, p); err != nil {
                                out.Flush()
                                fatalf("%s", err)
                        }
-                       if out.Count() > 0 {
-                               out.w.WriteRune('\n')
+                       if out.NeedNL() {
+                               out.Write([]byte{'\n'})
                        }
                }
        }
@@ -140,32 +139,33 @@ func runList(cmd *Command, args []string) {
        }
 }
 
-// CountingWriter counts its data, so we can avoid appending a newline
-// if there was no actual output.
-type CountingWriter struct {
-       w     *bufio.Writer
-       count int64
+// TrackingWriter tracks the last byte written on every write so
+// we can avoid printing a newline if one was already written or
+// if there is no output at all.
+type TrackingWriter struct {
+       w    *bufio.Writer
+       last byte
 }
 
-func newCountingWriter(w io.Writer) *CountingWriter {
-       return &CountingWriter{
-               w: bufio.NewWriter(w),
+func newTrackingWriter(w io.Writer) *TrackingWriter {
+       return &TrackingWriter{
+               w:    bufio.NewWriter(w),
+               last: '\n',
        }
 }
 
-func (cw *CountingWriter) Write(p []byte) (n int, err error) {
-       cw.count += int64(len(p))
-       return cw.w.Write(p)
-}
-
-func (cw *CountingWriter) Flush() {
-       cw.w.Flush()
+func (t *TrackingWriter) Write(p []byte) (n int, err error) {
+       n, err = t.w.Write(p)
+       if n > 0 {
+               t.last = p[n-1]
+       }
+       return
 }
 
-func (cw *CountingWriter) Reset() {
-       cw.count = 0
+func (t *TrackingWriter) Flush() {
+       t.w.Flush()
 }
 
-func (cw *CountingWriter) Count() int64 {
-       return cw.count
+func (t *TrackingWriter) NeedNL() bool {
+       return t.last != '\n'
 }