command: Replace `StdinSentinel` with an option

The `StdinSentinel` value can be passed to `WithStdin()` in order to
tell the command package to set up the command for `Write()`ing to it.
Replace this with a new option `WithSetupStdin()` so that we can avoid
the use of sentinel values.

7 files changed, 24 insertions, 16 deletions

diff --git a/internal/command/command.go b/internal/command/command.go
index 2ebd3d12f..5782e75dc 100644
--- a/internal/command/command.go
+++ b/internal/command/command.go
@@ -109,13 +109,6 @@ var (
 	// envInjector is responsible for injecting environment variables required for tracing into
 	// the child process.
 	envInjector = tracing.NewEnvInjector()
-
-	// SetupStdin instructs New() to configure the stdin pipe of the command it is creating.
-	// This allows you call Write() on the command as if it is an ordinary io.Writer, sending
-	// data directly to the stdin of the process.
-	//
-	// You should not call Read() on this value - it is strictly for configuration!
-	SetupStdin io.Reader = stdinSentinel{}
 )
 
 const (
@@ -210,9 +203,9 @@ func New(ctx context.Context, cmd *exec.Cmd, opts ...Option) (*Command, error) {
 
 	// Three possible values for stdin:
 	//   * nil - Go implicitly uses /dev/null
-	//   * SetupStdin - configure with cmd.StdinPipe(), allowing Write() to work
+	//   * stdinSentinel - configure with cmd.StdinPipe(), allowing Write() to work
 	//   * Another io.Reader - becomes cmd.Stdin. Write() will not work
-	if cfg.stdin == SetupStdin {
+	if _, ok := cfg.stdin.(stdinSentinel); ok {
 		pipe, err := cmd.StdinPipe()
 		if err != nil {
 			return nil, fmt.Errorf("GitCommand: stdin: %v", err)
diff --git a/internal/command/command_test.go b/internal/command/command_test.go
index 7bf69ba9c..dbe7d04dd 100644
--- a/internal/command/command_test.go
+++ b/internal/command/command_test.go
@@ -212,7 +212,7 @@ func TestNew_setupStdin(t *testing.T) {
 	stdin := "Test value"
 
 	var buf bytes.Buffer
-	cmd, err := New(ctx, exec.Command("cat"), WithStdin(SetupStdin), WithStdout(&buf))
+	cmd, err := New(ctx, exec.Command("cat"), WithSetupStdin(), WithStdout(&buf))
 	require.NoError(t, err)
 
 	_, err = fmt.Fprintf(cmd, "%s", stdin)
diff --git a/internal/command/option.go b/internal/command/option.go
index f31602254..7e4c0c64f 100644
--- a/internal/command/option.go
+++ b/internal/command/option.go
@@ -13,15 +13,22 @@ type config struct {
 // created.
 type Option func(cfg *config)
 
-// WithStdin sets up the command to read from the given reader. If stdin is specified as SetupStdin,
-// you will be able to write to the stdin of the subprocess by calling Write() on the returned
-// Command.
+// WithStdin sets up the command to read from the given reader.
 func WithStdin(stdin io.Reader) Option {
 	return func(cfg *config) {
 		cfg.stdin = stdin
 	}
 }
 
+// WithSetupStdin instructs New() to configure the stdin pipe of the command it is creating. This
+// allows you call Write() on the command as if it is an ordinary io.Writer, sending data directly
+// to the stdin of the process.
+func WithSetupStdin() Option {
+	return func(cfg *config) {
+		cfg.stdin = stdinSentinel{}
+	}
+}
+
 // WithStdout sets up the command to write standard output to the given writer.
 func WithStdout(stdout io.Writer) Option {
 	return func(cfg *config) {
diff --git a/internal/git/catfile/object_info_reader.go b/internal/git/catfile/object_info_reader.go
index f391bd128..84857ce70 100644
--- a/internal/git/catfile/object_info_reader.go
+++ b/internal/git/catfile/object_info_reader.go
@@ -146,7 +146,7 @@ func newObjectInfoReader(
 				git.Flag{Name: "--buffer"},
 			},
 		},
-		git.WithStdin(command.SetupStdin),
+		git.WithSetupStdin(),
 	)
 	if err != nil {
 		return nil, err
diff --git a/internal/git/catfile/object_reader.go b/internal/git/catfile/object_reader.go
index 4810a8207..516050301 100644
--- a/internal/git/catfile/object_reader.go
+++ b/internal/git/catfile/object_reader.go
@@ -67,7 +67,7 @@ func newObjectReader(
 				git.Flag{Name: "--buffer"},
 			},
 		},
-		git.WithStdin(command.SetupStdin),
+		git.WithSetupStdin(),
 	)
 	if err != nil {
 		return nil, err
diff --git a/internal/git/command_options.go b/internal/git/command_options.go
index ffa7e402c..f2ed3bb04 100644
--- a/internal/git/command_options.go
+++ b/internal/git/command_options.go
@@ -185,6 +185,14 @@ func WithStdin(r io.Reader) CmdOpt {
 	}
 }
 
+// WithSetupStdin sets up the command so that it can be `Write()`en to.
+func WithSetupStdin() CmdOpt {
+	return func(_ context.Context, _ config.Cfg, _ CommandFactory, c *cmdCfg) error {
+		c.commandOpts = append(c.commandOpts, command.WithSetupStdin())
+		return nil
+	}
+}
+
 // WithStdout sets the command's stdout.
 func WithStdout(w io.Writer) CmdOpt {
 	return func(_ context.Context, _ config.Cfg, _ CommandFactory, c *cmdCfg) error {
diff --git a/internal/git/updateref/updateref.go b/internal/git/updateref/updateref.go
index a00f78c3e..cc97513cc 100644
--- a/internal/git/updateref/updateref.go
+++ b/internal/git/updateref/updateref.go
@@ -63,7 +63,7 @@ func New(ctx context.Context, repo git.RepositoryExecutor, opts ...UpdaterOpt) (
 			Flags: []git.Option{git.Flag{Name: "-z"}, git.Flag{Name: "--stdin"}},
 		},
 		txOption,
-		git.WithStdin(command.SetupStdin),
+		git.WithSetupStdin(),
 		git.WithStderr(&stderr),
 	)
 	if err != nil {