Add preview border style 'line'

It draws a single line between the preview window and the rest of the
interface. i.e. automatically choose between 'left', 'right', 'top', and
'bottom' depending on the position of the preview window.

5 files changed, 70 insertions, 27 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e18790b8..e0b8e66e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,7 @@ CHANGELOG
         - `change-header-label`
         - `transform-header-label`
 - Added `--preview-border[=STYLE]` as short for `--preview-window=border[-STYLE]`
+- Added new preview border style `line` which draws a single separator line between the preview window and the rest of the interface
 - You can specify `border-native` to `--tmux` so that native tmux border is used instead of `--border`. This can be useful if you start a different program from inside the popup.
   ```sh
   fzf --tmux border-native --bind 'enter:execute:less {}'
diff --git a/man/man1/fzf.1 b/man/man1/fzf.1
index 16421c7b..cc80c1a4 100644
--- a/man/man1/fzf.1
+++ b/man/man1/fzf.1
@@ -775,7 +775,10 @@ e.g.
 
 .TP
 .BI "\-\-preview\-border" [=STYLE]
-Short for \fB\-\-preview\-window=border\-STYLE\fR
+Short for \fB\-\-preview\-window=border\-STYLE\fR. In addition to the other
+styles, \fBline\fR style is also supported for preview border, which draws
+a single separator line between the preview window and the rest of the
+interface.
 
 .TP
 .BI "\-\-preview\-label" [=LABEL]
@@ -812,7 +815,7 @@ default value 0 (or \fBcenter\fR) will put the label at the center of the
 border line.
 
 .TP
-.BI "\-\-preview\-window=" "[POSITION][,SIZE[%]][,border\-BORDER_OPT][,[no]wrap][,[no]follow][,[no]cycle][,[no]info][,[no]hidden][,+SCROLL[OFFSETS][/DENOM]][,~HEADER_LINES][,default][,<SIZE_THRESHOLD(ALTERNATIVE_LAYOUT)]"
+.BI "\-\-preview\-window=" "[POSITION][,SIZE[%]][,border\-STYLE][,[no]wrap][,[no]follow][,[no]cycle][,[no]info][,[no]hidden][,+SCROLL[OFFSETS][/DENOM]][,~HEADER_LINES][,default][,<SIZE_THRESHOLD(ALTERNATIVE_LAYOUT)]"
 
 .RS
 .B POSITION: (default: right)
@@ -855,6 +858,10 @@ e.g. \fBborder\-rounded\fR (border with rounded edges, default),
 \fBborder\-sharp\fR (border with sharp edges), \fBborder\-left\fR,
 \fBborder\-none\fR, etc.
 
+* In addition to the other border styles, \fBborder\-line\fR style is also
+supported, which draws a single separator line between the preview window and
+the rest of the interface.
+
 * \fB[:+SCROLL[OFFSETS][/DENOM]]\fR determines the initial scroll offset of the
 preview window.
 
diff --git a/src/options.go b/src/options.go
index f6b7245f..7db7418b 100644
--- a/src/options.go
+++ b/src/options.go
@@ -146,10 +146,12 @@ Usage: fzf [options]
     --preview-window=OPT     Preview window layout (default: right:50%)
                              [up|down|left|right][,SIZE[%]]
                              [,[no]wrap][,[no]cycle][,[no]follow][,[no]info]
-                             [,[no]hidden][,border-BORDER_OPT]
+                             [,[no]hidden][,border-STYLE]
                              [,+SCROLL[OFFSETS][/DENOM]][,~HEADER_LINES]
                              [,default][,<SIZE_THRESHOLD(ALTERNATIVE_LAYOUT)]
     --preview-border[=STYLE] Short for --preview-window=border-STYLE
+                             [rounded|sharp|bold|block|thinblock|double|horizontal|vertical|
+                              top|bottom|left|right|line|none] (default: rounded)
     --preview-label=LABEL
     --preview-label-pos=N    Same as --border-label and --border-label-pos,
                              but for preview window
@@ -313,6 +315,10 @@ func (o *previewOpts) Toggle() {
 	o.hidden = !o.hidden
 }
 
+func (o *previewOpts) HasBorderRight() bool {
+	return o.border.HasRight() || o.border == tui.BorderLine && o.position == posLeft
+}
+
 func defaultTmuxOptions(index int) *tmuxOptions {
 	return &tmuxOptions{
 		position: posCenter,
@@ -832,8 +838,13 @@ func processScheme(opts *Options) error {
 	return nil
 }
 
-func parseBorder(str string, optional bool) (tui.BorderShape, error) {
+func parseBorder(str string, optional bool, allowLine bool) (tui.BorderShape, error) {
 	switch str {
+	case "line":
+		if !allowLine {
+			return tui.BorderNone, errors.New("'line' is only allowed for preview border")
+		}
+		return tui.BorderLine, nil
 	case "rounded":
 		return tui.BorderRounded, nil
 	case "sharp":
@@ -1900,6 +1911,8 @@ func parsePreviewWindowImpl(opts *previewOpts, input string) error {
 			opts.position = posRight
 		case "rounded", "border", "border-rounded":
 			opts.border = tui.BorderRounded
+		case "border-line":
+			opts.border = tui.BorderLine
 		case "sharp", "border-sharp":
 			opts.border = tui.BorderSharp
 		case "border-bold":
@@ -2501,7 +2514,7 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 		case "--no-preview":
 			opts.Preview.command = ""
 		case "--preview-window":
-			str, err := nextString(allArgs, &i, "preview window layout required: [up|down|left|right][,SIZE[%]][,border-BORDER_OPT][,wrap][,cycle][,hidden][,+SCROLL[OFFSETS][/DENOM]][,~HEADER_LINES][,default]")
+			str, err := nextString(allArgs, &i, "preview window layout required: [up|down|left|right][,SIZE[%]][,border-STYLE][,wrap][,cycle][,hidden][,+SCROLL[OFFSETS][/DENOM]][,~HEADER_LINES][,default]")
 			if err != nil {
 				return err
 			}
@@ -2512,7 +2525,7 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			opts.Preview.border = tui.BorderNone
 		case "--preview-border":
 			hasArg, arg := optionalNextString(allArgs, &i)
-			if opts.Preview.border, err = parseBorder(arg, !hasArg); err != nil {
+			if opts.Preview.border, err = parseBorder(arg, !hasArg, true); err != nil {
 				return err
 			}
 		case "--height":
@@ -2537,12 +2550,12 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			opts.BorderShape = tui.BorderNone
 		case "--border":
 			hasArg, arg := optionalNextString(allArgs, &i)
-			if opts.BorderShape, err = parseBorder(arg, !hasArg); err != nil {
+			if opts.BorderShape, err = parseBorder(arg, !hasArg, false); err != nil {
 				return err
 			}
 		case "--list-border":
 			hasArg, arg := optionalNextString(allArgs, &i)
-			if opts.ListBorderShape, err = parseBorder(arg, !hasArg); err != nil {
+			if opts.ListBorderShape, err = parseBorder(arg, !hasArg, false); err != nil {
 				return err
 			}
 		case "--no-list-border":
@@ -2566,7 +2579,7 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			opts.HeaderBorderShape = tui.BorderNone
 		case "--header-border":
 			hasArg, arg := optionalNextString(allArgs, &i)
-			if opts.HeaderBorderShape, err = parseBorder(arg, !hasArg); err != nil {
+			if opts.HeaderBorderShape, err = parseBorder(arg, !hasArg, false); err != nil {
 				return err
 			}
 		case "--no-header-label":
@@ -2587,7 +2600,7 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			opts.InputBorderShape = tui.BorderNone
 		case "--input-border":
 			hasArg, arg := optionalNextString(allArgs, &i)
-			if opts.InputBorderShape, err = parseBorder(arg, !hasArg); err != nil {
+			if opts.InputBorderShape, err = parseBorder(arg, !hasArg, false); err != nil {
 				return err
 			}
 		case "--no-input-label":
@@ -2738,15 +2751,15 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			} else if match, value := optString(arg, "-d", "--delimiter="); match {
 				opts.Delimiter = delimiterRegexp(value)
 			} else if match, value := optString(arg, "--border="); match {
-				if opts.BorderShape, err = parseBorder(value, false); err != nil {
+				if opts.BorderShape, err = parseBorder(value, false, false); err != nil {
 					return err
 				}
 			} else if match, value := optString(arg, "--preview-border="); match {
-				if opts.Preview.border, err = parseBorder(value, false); err != nil {
+				if opts.Preview.border, err = parseBorder(value, false, true); err != nil {
 					return err
 				}
 			} else if match, value := optString(arg, "--list-border="); match {
-				if opts.ListBorderShape, err = parseBorder(value, false); err != nil {
+				if opts.ListBorderShape, err = parseBorder(value, false, false); err != nil {
 					return err
 				}
 			} else if match, value := optString(arg, "--list-label="); match {
@@ -2756,7 +2769,7 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 					return err
 				}
 			} else if match, value := optString(arg, "--input-border="); match {
-				if opts.InputBorderShape, err = parseBorder(value, false); err != nil {
+				if opts.InputBorderShape, err = parseBorder(value, false, false); err != nil {
 					return err
 				}
 			} else if match, value := optString(arg, "--input-label="); match {
diff --git a/src/terminal.go b/src/terminal.go
index 764284a9..344246de 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -1513,7 +1513,7 @@ func (t *Terminal) minPreviewSize(opts *previewOpts) (int, int) {
 
 	switch opts.position {
 	case posLeft, posRight:
-		if len(t.scrollbar) > 0 && !opts.border.HasRight() {
+		if len(t.scrollbar) > 0 && !opts.HasBorderRight() {
 			// Need a column to show scrollbar
 			minPreviewWidth++
 		}
@@ -1757,17 +1757,30 @@ func (t *Terminal) resizeWindows(forcePreview bool, redrawBorder bool) {
 			createPreviewWindow := func(y int, x int, w int, h int) {
 				pwidth := w
 				pheight := h
-				previewBorder := tui.MakeBorderStyle(previewOpts.border, t.unicode)
+				shape := previewOpts.border
+				if shape == tui.BorderLine {
+					switch previewOpts.position {
+					case posUp:
+						shape = tui.BorderBottom
+					case posDown:
+						shape = tui.BorderTop
+					case posLeft:
+						shape = tui.BorderRight
+					case posRight:
+						shape = tui.BorderLeft
+					}
+				}
+				previewBorder := tui.MakeBorderStyle(shape, t.unicode)
 				t.pborder = t.tui.NewWindow(y, x, w, h, tui.WindowPreview, previewBorder, false)
-				pwidth -= borderColumns(previewOpts.border, bw)
-				pheight -= borderLines(previewOpts.border)
-				if previewOpts.border.HasLeft() {
+				pwidth -= borderColumns(shape, bw)
+				pheight -= borderLines(shape)
+				if shape.HasLeft() {
 					x += 1 + bw
 				}
-				if previewOpts.border.HasTop() {
+				if shape.HasTop() {
 					y += 1
 				}
-				if len(t.scrollbar) > 0 && !previewOpts.border.HasRight() {
+				if len(t.scrollbar) > 0 && !shape.HasRight() {
 					// Need a column to show scrollbar
 					pwidth -= 1
 				}
@@ -1800,6 +1813,14 @@ func (t *Terminal) resizeWindows(forcePreview bool, redrawBorder bool) {
 				if previewOpts.hidden {
 					return
 				}
+				// If none of the inner borders has the right side, but the outer border does, increase the width by 1 column
+				stickToRight = t.borderShape.HasRight() &&
+					!previewOpts.HasBorderRight() && !t.listBorderShape.HasRight() && !t.inputBorderShape.HasRight() &&
+					(!t.headerVisible || !t.headerBorderShape.HasRight() || t.visibleHeaderLines() == 0)
+				if stickToRight {
+					innerWidth++
+					width++
+				}
 
 				maxPreviewLines := availableLines
 				if t.wborder != nil {
@@ -1870,7 +1891,7 @@ func (t *Terminal) resizeWindows(forcePreview bool, redrawBorder bool) {
 					createPreviewWindow(marginInt[0], marginInt[3], pwidth, height)
 				} else {
 					// NOTE: fzf --preview 'cat {}' --preview-window border-left --border
-					stickToRight = !previewOpts.border.HasRight() && t.borderShape.HasRight()
+					stickToRight = !previewOpts.HasBorderRight() && t.borderShape.HasRight()
 					if stickToRight {
 						innerWidth++
 						width++
@@ -3187,7 +3208,7 @@ func (t *Terminal) renderPreviewScrollbar(yoff int, barLength int, barStart int)
 		t.previewer.xw = xw
 	}
 	xshift := -1 - t.borderWidth
-	if !t.activePreviewOpts.border.HasRight() {
+	if !t.activePreviewOpts.HasBorderRight() {
 		xshift = -1
 	}
 	yshift := 1
diff --git a/src/tui/tui.go b/src/tui/tui.go
index db846f75..2bd9caf9 100644
--- a/src/tui/tui.go
+++ b/src/tui/tui.go
@@ -358,6 +358,7 @@ type BorderShape int
 
 const (
 	BorderUndefined BorderShape = iota
+	BorderLine
 	BorderNone
 	BorderRounded
 	BorderSharp
@@ -375,7 +376,7 @@ const (
 
 func (s BorderShape) HasLeft() bool {
 	switch s {
-	case BorderNone, BorderRight, BorderTop, BorderBottom, BorderHorizontal: // No Left
+	case BorderNone, BorderLine, BorderRight, BorderTop, BorderBottom, BorderHorizontal: // No Left
 		return false
 	}
 	return true
@@ -383,7 +384,7 @@ func (s BorderShape) HasLeft() bool {
 
 func (s BorderShape) HasRight() bool {
 	switch s {
-	case BorderNone, BorderLeft, BorderTop, BorderBottom, BorderHorizontal: // No right
+	case BorderNone, BorderLine, BorderLeft, BorderTop, BorderBottom, BorderHorizontal: // No right
 		return false
 	}
 	return true
@@ -391,7 +392,7 @@ func (s BorderShape) HasRight() bool {
 
 func (s BorderShape) HasTop() bool {
 	switch s {
-	case BorderNone, BorderLeft, BorderRight, BorderBottom, BorderVertical: // No top
+	case BorderNone, BorderLine, BorderLeft, BorderRight, BorderBottom, BorderVertical: // No top
 		return false
 	}
 	return true
@@ -399,7 +400,7 @@ func (s BorderShape) HasTop() bool {
 
 func (s BorderShape) HasBottom() bool {
 	switch s {
-	case BorderNone, BorderLeft, BorderRight, BorderTop, BorderVertical: // No bottom
+	case BorderNone, BorderLine, BorderLeft, BorderRight, BorderTop, BorderVertical: // No bottom
 		return false
 	}
 	return true