Add `border-native` option to `--tmux` flag (#4157)

This commit adds the `border-native` resulting in the following:

```
--tmux[=[center|top|bottom|left|right][,SIZE[%]][,SIZE[%]][,border-native]]
```

By default, when not specified, the `-B` flag is passed to the
`tmux popup-window` command such that no border is drawn around
the tmux popup window.

When the `border-native` option is present, the `-B` flag is omitted
and the popup window is drawn using the border style configured in
the tmux config file.

Fixes #4156

Signed-off-by: Andreas Auernhammer <github@aead.dev>
Co-authored-by: Junegunn Choi <junegunn.c@gmail.com>

2 files changed, 23 insertions, 8 deletions

diff --git a/src/options.go b/src/options.go
index 0b6250f3..a3096d11 100644
--- a/src/options.go
+++ b/src/options.go
@@ -77,7 +77,7 @@ Usage: fzf [options]
                              (default: 10)
     --tmux[=OPTS]            Start fzf in a tmux popup (requires tmux 3.3+)
                              [center|top|bottom|left|right][,SIZE[%]][,SIZE[%]]
-                             (default: center,50%)
+                             [,border-native] (default: center,50%)
     --layout=LAYOUT          Choose layout: [default|reverse|reverse-list]
     --border[=STYLE]         Draw border around the finder
                              [rounded|sharp|bold|block|thinblock|double|horizontal|vertical|
@@ -254,6 +254,7 @@ type tmuxOptions struct {
 	height   sizeSpec
 	position windowPosition
 	index    int
+	border   bool
 }
 
 type layoutType int
@@ -316,11 +317,19 @@ func parseTmuxOptions(arg string, index int) (*tmuxOptions, error) {
 	var err error
 	opts := defaultTmuxOptions(index)
 	tokens := splitRegexp.Split(arg, -1)
-	errorToReturn := errors.New("invalid tmux option: " + arg + " (expected: [center|top|bottom|left|right][,SIZE[%]][,SIZE[%]])")
-	if len(tokens) == 0 || len(tokens) > 3 {
+	errorToReturn := errors.New("invalid tmux option: " + arg + " (expected: [center|top|bottom|left|right][,SIZE[%]][,SIZE[%][,border-native]])")
+	if len(tokens) == 0 || len(tokens) > 4 {
 		return nil, errorToReturn
 	}
 
+	for i, token := range tokens {
+		if token == "border-native" {
+			tokens = append(tokens[:i], tokens[i+1:]...) // cut the 'border-native' option
+			opts.border = true
+			break
+		}
+	}
+
 	// Defaults to 'center'
 	switch tokens[0] {
 	case "top", "up":
diff --git a/src/tmux.go b/src/tmux.go
index b2315dcd..e459000a 100644
--- a/src/tmux.go
+++ b/src/tmux.go
@@ -9,13 +9,16 @@ import (
 
 func runTmux(args []string, opts *Options) (int, error) {
 	// Prepare arguments
-	fzf := args[0]
-	args = append([]string{"--bind=ctrl-z:ignore"}, args[1:]...)
-	if opts.BorderShape == tui.BorderUndefined {
+	fzf, rest := args[0], args[1:]
+	args = []string{"--bind=ctrl-z:ignore"}
+	if !opts.Tmux.border && opts.BorderShape == tui.BorderUndefined {
 		args = append(args, "--border")
 	}
+	if opts.Tmux.border && opts.Margin == defaultMargin() {
+		args = append(args, "--margin=0,1")
+	}
 	argStr := escapeSingleQuote(fzf)
-	for _, arg := range args {
+	for _, arg := range append(args, rest...) {
 		argStr += " " + escapeSingleQuote(arg)
 	}
 	argStr += ` --no-tmux --no-height`
@@ -33,7 +36,10 @@ func runTmux(args []string, opts *Options) (int, error) {
 	// M        Both    The mouse position
 	// W        Both    The window position on the status line
 	// S        -y      The line above or below the status line
-	tmuxArgs := []string{"display-popup", "-E", "-B", "-d", dir}
+	tmuxArgs := []string{"display-popup", "-E", "-d", dir}
+	if !opts.Tmux.border {
+		tmuxArgs = append(tmuxArgs, "-B")
+	}
 	switch opts.Tmux.position {
 	case posUp:
 		tmuxArgs = append(tmuxArgs, "-xC", "-y0")