Fix test

src/please.go

@@ -1209,7 +1209,15 @@ type TargetsOrArgs []TargetOrArg
 func (l TargetsOrArgs) Separate() (annotated []core.AnnotatedOutputLabel, unannotated []core.BuildLabel, args []string) {
 	for _, arg := range l {
 		if l, _ := arg.label.Label(); l.IsEmpty() {
-			args = append(args, arg.arg)
+			if arg.arg == "-" {
+				labels := plz.ReadAndParseStdinLabels()
+				unannotated = append(unannotated, labels...)
+				for _, label := range labels {
+					annotated = append(annotated, core.AnnotatedOutputLabel{BuildLabel: label})
+				}
+			} else {
+				args = append(args, arg.arg)
+			}
 		} else {
 			annotated = append(annotated, arg.label)
 			unannotated = append(unannotated, arg.label.BuildLabel)

src/plz/plz.go

@@ -239,16 +239,23 @@ func ReadStdinLabels(labels []core.BuildLabel) []core.BuildLabel {
 	ret := []core.BuildLabel{}
 	for _, l := range labels {
 		if l == core.BuildLabelStdin {
-			for s := range flags.ReadStdin() {
-				ret = append(ret, core.ParseBuildLabels([]string{s})...)
-			}
+			ret = append(ret, ReadAndParseStdinLabels()...)
 		} else {
 			ret = append(ret, l)
 		}
 	}
 	return ret
 }
 
+// ReadAndParseStdinLabels unconditionally reads stdin and parses it into build labels.
+func ReadAndParseStdinLabels() []core.BuildLabel {
+	ret := []core.BuildLabel{}
+	for s := range flags.ReadStdin() {
+		ret = append(ret, core.ParseBuildLabels([]string{s})...)
+	}
+	return ret
+}
+
 // A limiter allows only a certain number of concurrent tasks
 // TODO(peterebden): We have about four of these now, commonise this somewhere
 type limiter chan struct{}