remove IOPreferenceNil

It doesn't really mean much of anything to specify IOPreferenceNil.
Nothing uses it, which isn't surprising because it's not clear what it
would even mean anywhere other than the begin/end of a pipeline.

Author: znull

pipe/command.go

@@ -70,18 +70,10 @@ func (s *commandStage) Name() string {
 }
 
 func (s *commandStage) Preferences() StagePreferences {
-	prefs := StagePreferences{
+	return StagePreferences{
 		StdinPreference:  IOPreferenceFile,
 		StdoutPreference: IOPreferenceFile,
 	}
-	if s.cmd.Stdin != nil {
-		prefs.StdinPreference = IOPreferenceNil
-	}
-	if s.cmd.Stdout != nil {
-		prefs.StdoutPreference = IOPreferenceNil
-	}
-
-	return prefs
 }
 
 func (s *commandStage) Start(

pipe/pipe_matching_test.go

@@ -22,6 +22,12 @@ import (
 const (
 	IOPreferenceUndefinedNopCloser pipe.IOPreference = iota + 100
 	IOPreferenceFileNopCloser
+
+	// expectNil is a test-only expectation token meaning that the
+	// stage should be passed a `nil` stdin / stdout (which happens at
+	// the beginning / end of a pipeline when no overall stdin / stdout
+	// is configured). It is not a real `IOPreference`.
+	expectNil
 )
 
 func file(t *testing.T) *os.File {
@@ -143,7 +149,7 @@ func prefString(pref pipe.IOPreference) string {
 		return "other"
 	case pipe.IOPreferenceFile:
 		return "*os.File"
-	case pipe.IOPreferenceNil:
+	case expectNil:
 		return "nil"
 	case IOPreferenceUndefinedNopCloser:
 		return "nopCloser(other)"
@@ -200,7 +206,7 @@ func TestPipeTypes(t *testing.T) {
 			name: "func",
 			opts: []pipe.Option{},
 			stages: []pipe.Stage{
-				newPipeSniffingFunc(pipe.IOPreferenceNil, pipe.IOPreferenceNil),
+				newPipeSniffingFunc(expectNil, expectNil),
 			},
 		},
 		{
@@ -209,7 +215,7 @@ func TestPipeTypes(t *testing.T) {
 				pipe.WithStdin(file(t)),
 			},
 			stages: []pipe.Stage{
-				newPipeSniffingFunc(IOPreferenceFileNopCloser, pipe.IOPreferenceNil),
+				newPipeSniffingFunc(IOPreferenceFileNopCloser, expectNil),
 			},
 		},
 		{
@@ -218,7 +224,7 @@ func TestPipeTypes(t *testing.T) {
 				pipe.WithStdout(file(t)),
 			},
 			stages: []pipe.Stage{
-				newPipeSniffingFunc(pipe.IOPreferenceNil, IOPreferenceFileNopCloser),
+				newPipeSniffingFunc(expectNil, IOPreferenceFileNopCloser),
 			},
 		},
 		{
@@ -227,7 +233,7 @@ func TestPipeTypes(t *testing.T) {
 				pipe.WithStdoutCloser(file(t)),
 			},
 			stages: []pipe.Stage{
-				newPipeSniffingFunc(pipe.IOPreferenceNil, pipe.IOPreferenceFile),
+				newPipeSniffingFunc(expectNil, pipe.IOPreferenceFile),
 			},
 		},
 		{
@@ -244,7 +250,7 @@ func TestPipeTypes(t *testing.T) {
 			name: "cmd",
 			opts: []pipe.Option{},
 			stages: []pipe.Stage{
-				newPipeSniffingCmd(pipe.IOPreferenceNil, pipe.IOPreferenceNil),
+				newPipeSniffingCmd(expectNil, expectNil),
 			},
 		},
 		{
@@ -253,7 +259,7 @@ func TestPipeTypes(t *testing.T) {
 				pipe.WithStdin(file(t)),
 			},
 			stages: []pipe.Stage{
-				newPipeSniffingCmd(IOPreferenceFileNopCloser, pipe.IOPreferenceNil),
+				newPipeSniffingCmd(IOPreferenceFileNopCloser, expectNil),
 			},
 		},
 		{
@@ -262,7 +268,7 @@ func TestPipeTypes(t *testing.T) {
 				pipe.WithStdout(file(t)),
 			},
 			stages: []pipe.Stage{
-				newPipeSniffingCmd(pipe.IOPreferenceNil, IOPreferenceFileNopCloser),
+				newPipeSniffingCmd(expectNil, IOPreferenceFileNopCloser),
 			},
 		},
 		{
@@ -271,7 +277,7 @@ func TestPipeTypes(t *testing.T) {
 				pipe.WithStdoutCloser(file(t)),
 			},
 			stages: []pipe.Stage{
-				newPipeSniffingCmd(pipe.IOPreferenceNil, pipe.IOPreferenceFile),
+				newPipeSniffingCmd(expectNil, pipe.IOPreferenceFile),
 			},
 		},
 		{
@@ -301,7 +307,7 @@ func TestPipeTypes(t *testing.T) {
 				pipe.WithStdout(file(t)),
 			},
 			stages: []pipe.Stage{
-				newPipeSniffingFunc(pipe.IOPreferenceNil, pipe.IOPreferenceFile),
+				newPipeSniffingFunc(expectNil, pipe.IOPreferenceFile),
 				newPipeSniffingCmd(pipe.IOPreferenceFile, IOPreferenceFileNopCloser),
 			},
 		},
@@ -312,23 +318,23 @@ func TestPipeTypes(t *testing.T) {
 			},
 			stages: []pipe.Stage{
 				newPipeSniffingCmd(IOPreferenceUndefinedNopCloser, pipe.IOPreferenceFile),
-				newPipeSniffingFunc(pipe.IOPreferenceFile, pipe.IOPreferenceNil),
+				newPipeSniffingFunc(pipe.IOPreferenceFile, expectNil),
 			},
 		},
 		{
 			name: "cmd-cmd",
 			opts: []pipe.Option{},
 			stages: []pipe.Stage{
-				newPipeSniffingCmd(pipe.IOPreferenceNil, pipe.IOPreferenceFile),
-				newPipeSniffingCmd(pipe.IOPreferenceFile, pipe.IOPreferenceNil),
+				newPipeSniffingCmd(expectNil, pipe.IOPreferenceFile),
+				newPipeSniffingCmd(pipe.IOPreferenceFile, expectNil),
 			},
 		},
 		{
 			name: "hybrid1",
 			opts: []pipe.Option{},
 			stages: []pipe.Stage{
 				newPipeSniffingStage(
-					pipe.IOPreferenceUndefined, pipe.IOPreferenceNil,
+					pipe.IOPreferenceUndefined, expectNil,
 					pipe.IOPreferenceUndefined, pipe.IOPreferenceUndefined,
 				),
 				newPipeSniffingStage(
@@ -337,7 +343,7 @@ func TestPipeTypes(t *testing.T) {
 				),
 				newPipeSniffingStage(
 					pipe.IOPreferenceUndefined, pipe.IOPreferenceFile,
-					pipe.IOPreferenceUndefined, pipe.IOPreferenceNil,
+					pipe.IOPreferenceUndefined, expectNil,
 				),
 			},
 		},
@@ -346,7 +352,7 @@ func TestPipeTypes(t *testing.T) {
 			opts: []pipe.Option{},
 			stages: []pipe.Stage{
 				newPipeSniffingStage(
-					pipe.IOPreferenceUndefined, pipe.IOPreferenceNil,
+					pipe.IOPreferenceUndefined, expectNil,
 					pipe.IOPreferenceUndefined, pipe.IOPreferenceFile,
 				),
 				newPipeSniffingStage(
@@ -355,7 +361,7 @@ func TestPipeTypes(t *testing.T) {
 				),
 				newPipeSniffingStage(
 					pipe.IOPreferenceUndefined, pipe.IOPreferenceUndefined,
-					pipe.IOPreferenceUndefined, pipe.IOPreferenceNil,
+					pipe.IOPreferenceUndefined, expectNil,
 				),
 			},
 		},

pipe/stage.go

@@ -138,9 +138,4 @@ const (
 	// IOPreferenceFile indicates that the stage would prefer for the
 	// specified stdin / stdout to be an `*os.File`, to avoid copying.
 	IOPreferenceFile
-
-	// IOPreferenceNil indicates that the stage does not use the
-	// specified stdin / stdout, so `nil` should be passed in. This
-	// should only happen at the beginning / end of a pipeline.
-	IOPreferenceNil
 )