Allow customizing scrollbar of the preview window via --scrollbar=xy

CHANGELOG.md

@@ -5,6 +5,15 @@ CHANGELOG
 ------
 - Added color name `preview-border` and `preview-scrollbar`
 - Added new border style `block` which uses [block elements](https://en.wikipedia.org/wiki/Block_Elements)
+- `--scrollbar` can take two characters, one for the main window, the other
+  for the preview window
+- Putting it altogether
+  ```sh
+  fzf-tmux -p 80% --padding 1,2 --preview 'bat --style=plain --color=always {}' \
+      --color 'bg:#222233,bg+:#333344,gutter:#222233,border:#111122,scrollbar:#ffaa00' \
+      --color 'preview-bg:#332233,preview-border:#222222,preview-scrollbar:#00aaff' \
+      --preview-window 'border-block' --border block --scrollbar '▌▐'
+  ```
 - Bug fixes and improvements
 
 0.40.0

man/man1/fzf.1

@@ -377,9 +377,10 @@ Do not display horizontal separator on the info line. A synonym for
 \fB--separator=''\fB
 
 .TP
-.BI "--scrollbar=" "CHAR"
+.BI "--scrollbar=" "CHAR1[CHAR2]"
 Use the given character to render scrollbar. (default: '│' or ':' depending on
-\fB--no-unicode\fR).
+\fB--no-unicode\fR). The optional \fBCHAR2\fR is used to render scrollbar of
+the preview window.
 
 .TP
 .B "--no-scrollbar"

src/options.go

@@ -75,7 +75,7 @@ const usage = `usage: fzf [options]
     --info=STYLE           Finder info style [default|hidden|inline|inline:SEPARATOR]
     --separator=STR        String to form horizontal separator on info line
     --no-separator         Hide info line separator
-    --scrollbar[=CHAR]     Scrollbar character
+    --scrollbar[=C1[C2]]   Scrollbar character(s) (each for main and preview window)
     --no-scrollbar         Hide scrollbar
     --prompt=STR           Input prompt (default: '> ')
     --pointer=STR          Pointer to the current line (default: '>')
@@ -1960,8 +1960,16 @@ func postProcessOptions(opts *Options) {
 		errorExit("--height option is currently not supported on this platform")
 	}
 
-	if opts.Scrollbar != nil && runewidth.StringWidth(*opts.Scrollbar) > 1 {
-		errorExit("scrollbar display width should be 1")
+	if opts.Scrollbar != nil {
+		runes := []rune(*opts.Scrollbar)
+		if len(runes) > 2 {
+			errorExit("--scrollbar should be given one or two characters")
+		}
+		for _, r := range runes {
+			if runewidth.RuneWidth(r) != 1 {
+				errorExit("scrollbar display width should be 1")
+			}
+		}
 	}
 
 	// Default actions for CTRL-N / CTRL-P when --history is set

src/terminal.go

@@ -199,6 +199,7 @@ type Terminal struct {
 	header0            []string
 	ellipsis           string
 	scrollbar          string
+	previewScrollbar   string
 	ansi               bool
 	tabstop            int
 	margin             [4]sizeSpec
@@ -690,8 +691,16 @@ func NewTerminal(opts *Options, eventBox *util.EventBox) *Terminal {
 		} else {
 			t.scrollbar = "|"
 		}
+		t.previewScrollbar = t.scrollbar
 	} else {
-		t.scrollbar = *opts.Scrollbar
+		runes := []rune(*opts.Scrollbar)
+		if len(runes) > 0 {
+			t.scrollbar = string(runes[0])
+			t.previewScrollbar = t.scrollbar
+			if len(runes) > 1 {
+				t.previewScrollbar = string(runes[1])
+			}
+		}
 	}
 
 	_, t.hasLoadActions = t.keymap[tui.Load.AsEvent()]
@@ -1956,7 +1965,7 @@ func (t *Terminal) renderPreviewScrollbar(yoff int, barLength int, barStart int)
 		t.previewer.bar[i] = bar
 		t.pborder.Move(y, x)
 		if i >= yoff+barStart && i < yoff+barStart+barLength {
-			t.pborder.CPrint(tui.ColPreviewScrollbar, t.scrollbar)
+			t.pborder.CPrint(tui.ColPreviewScrollbar, t.previewScrollbar)
 		} else {
 			t.pborder.CPrint(tui.ColPreviewScrollbar, " ")
 		}