Set --border-label as the title of the tmux floating pane (#4853)

The pane sets the options itself before running fzf, so that they are
in place no matter how quickly the command exits, targeted at
$TMUX_PANE; the default target would resolve to the active pane of
the session's current window.

- pane-border-format is set to '#{pane_title}' so that the label is
  displayed on the border when pane-border-status is enabled;
  pane-border-status itself is a window option in released tmux
  versions and is left alone
- When a border style is explicitly specified with --border, a popup
  is used instead of a floating pane so that the fzf-drawn border is
  the only border shown; give 'border-native' to force a floating pane
- 'none' and 'line' are treated as no border; fzf draws no box for
  either, so the label is displayed on the native border
- Remove 'border-fzf' which is now redundant; it was never released
- The title is escaped for select-pane -T which expands format
  expressions; a lone ';' is escaped as tmux would treat it as a
  command separator
- The label is skipped when ANSI stripping leaves an empty string
- --border-label-pos is ignored
- Fix remain-on-exit set on the original pane instead of the floating
  pane

src/options.go

@@ -77,7 +77,7 @@ Usage: fzf [options]
                              according to the other layout options (default: 10+).
     --popup[=OPTS]           Start fzf in a floating pane (requires tmux 3.3+ or Zellij 0.44+)
                              [center|top|bottom|left|right][,SIZE[%]][,SIZE[%]]
-                             [,border-native|border-fzf] (default: center,50%)
+                             [,border-native] (default: center,50%)
     --tmux[=OPTS]            Alias for --popup
 
   LAYOUT
@@ -335,20 +335,12 @@ const (
 	posNext // adjacent to the input section, on the list side
 )
 
-type tmuxBorder int
-
-const (
-	tmuxBorderAuto tmuxBorder = iota
-	tmuxBorderNative
-	tmuxBorderFzf
-)
-
 type tmuxOptions struct {
 	width    sizeSpec
 	height   sizeSpec
 	position windowPosition
 	index    int
-	border   tmuxBorder
+	border   bool
 }
 
 type layoutType int
@@ -435,19 +427,15 @@ func parseTmuxOptions(arg string, index int) (*tmuxOptions, error) {
 	var err error
 	opts := defaultTmuxOptions(index)
 	tokens := splitRegexp.Split(arg, -1)
-	errorToReturn := errors.New("invalid popup option: " + arg + " (expected: [center|top|bottom|left|right][,SIZE[%]][,SIZE[%]][,border-native|border-fzf])")
+	errorToReturn := errors.New("invalid popup 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" || token == "border-fzf" {
-			tokens = append(tokens[:i], tokens[i+1:]...) // cut the border option
-			if token == "border-native" {
-				opts.border = tmuxBorderNative
-			} else {
-				opts.border = tmuxBorderFzf
-			}
+		if token == "border-native" {
+			tokens = append(tokens[:i], tokens[i+1:]...) // cut the 'border-native' option
+			opts.border = true
 			break
 		}
 	}