Render UI directly to /dev/tty

See https://github.com/junegunn/fzf/discussions/3792

This allows us to separately capture the standard error from fzf and its
child processes, and there's less chance of user errors of redirecting
the error stream and hiding fzf.

3 files changed, 28 insertions, 5 deletions

diff --git a/src/tui/light.go b/src/tui/light.go
index 3ef8b60e..4d3f58a4 100644
--- a/src/tui/light.go
+++ b/src/tui/light.go
@@ -73,7 +73,7 @@ func (r *LightRenderer) csi(code string) string {
 
 func (r *LightRenderer) flush() {
 	if r.queued.Len() > 0 {
-		fmt.Fprint(os.Stderr, "\x1b[?7l\x1b[?25l"+r.queued.String()+"\x1b[?25h\x1b[?7h")
+		fmt.Fprint(r.ttyout, "\x1b[?7l\x1b[?25l"+r.queued.String()+"\x1b[?25h\x1b[?7h")
 		r.queued.Reset()
 	}
 }
@@ -88,6 +88,7 @@ type LightRenderer struct {
 	prevDownTime  time.Time
 	clicks        [][2]int
 	ttyin         *os.File
+	ttyout        *os.File
 	buffer        []byte
 	origState     *term.State
 	width         int
@@ -131,6 +132,10 @@ func NewLightRenderer(theme *ColorTheme, forceBlack bool, mouse bool, tabstop in
 	if err != nil {
 		return nil, err
 	}
+	out, err := openTtyOut()
+	if err != nil {
+		out = os.Stderr
+	}
 	r := LightRenderer{
 		closed:        util.NewAtomicBool(false),
 		theme:         theme,
@@ -138,6 +143,7 @@ func NewLightRenderer(theme *ColorTheme, forceBlack bool, mouse bool, tabstop in
 		mouse:         mouse,
 		clearOnExit:   clearOnExit,
 		ttyin:         in,
+		ttyout:        out,
 		yoffset:       0,
 		tabstop:       tabstop,
 		fullscreen:    fullscreen,
diff --git a/src/tui/light_unix.go b/src/tui/light_unix.go
index a5499a00..da675aa2 100644
--- a/src/tui/light_unix.go
+++ b/src/tui/light_unix.go
@@ -14,6 +14,8 @@ import (
 	"golang.org/x/term"
 )
 
+var tty string
+
 func IsLightRendererSupported() bool {
 	return true
 }
@@ -48,12 +50,14 @@ func (r *LightRenderer) closePlatform() {
 	// NOOP
 }
 
-func openTtyIn() (*os.File, error) {
-	in, err := os.OpenFile(consoleDevice, syscall.O_RDONLY, 0)
+func openTty(mode int) (*os.File, error) {
+	in, err := os.OpenFile(consoleDevice, mode, 0)
 	if err != nil {
-		tty := ttyname()
+		if len(tty) == 0 {
+			tty = ttyname()
+		}
 		if len(tty) > 0 {
-			if in, err := os.OpenFile(tty, syscall.O_RDONLY, 0); err == nil {
+			if in, err := os.OpenFile(tty, mode, 0); err == nil {
 				return in, nil
 			}
 		}
@@ -62,6 +66,14 @@ func openTtyIn() (*os.File, error) {
 	return in, nil
 }
 
+func openTtyIn() (*os.File, error) {
+	return openTty(syscall.O_RDONLY)
+}
+
+func openTtyOut() (*os.File, error) {
+	return openTty(syscall.O_WRONLY)
+}
+
 func (r *LightRenderer) setupTerminal() {
 	term.MakeRaw(r.fd())
 }
diff --git a/src/tui/light_windows.go b/src/tui/light_windows.go
index 635b8926..8c459d66 100644
--- a/src/tui/light_windows.go
+++ b/src/tui/light_windows.go
@@ -96,6 +96,11 @@ func openTtyIn() (*os.File, error) {
 	return nil, nil
 }
 
+func openTtyOut() (*os.File, error) {
+	// not used
+	return nil, nil
+}
+
 func (r *LightRenderer) setupTerminal() error {
 	if err := windows.SetConsoleMode(windows.Handle(r.outHandle), consoleFlagsOutput); err != nil {
 		return err