Allow displaying --nth parts in a different text style

Close #4183

8 files changed, 128 insertions, 36 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 75e873b2..5c772aa8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -82,6 +82,21 @@ Also, fzf now offers "style presets" for quick customization, which can be activ
   # Start with --nth 1, then 2, then 3, then back to the default, 1
   echo 'foo foobar foobarbaz' | fzf --bind 'space:change-nth(2|3|)' --nth 1 -q foo
   ```
+- `--nth` parts of each line can now be rendered in a different text style
+  ```sh
+  # nth in a different style
+  ls -al | fzf --nth -1 --color nth:italic
+  ls -al | fzf --nth -1 --color nth:reverse
+  ls -al | fzf --nth -1 --color nth:reverse:bold
+
+  # Dim the other parts
+  ls -al | fzf --nth -1 --color nth:regular,fg:dim,current-fg:dim
+
+  # With 'change-nth'
+  ps -ef | fzf --reverse --header-lines 1 --header-border bottom --input-border \
+               --color nth:regular,fg:dim,current-fg:dim \
+               --nth 8.. --bind 'ctrl-n:change-nth(..|1|2|3|4|5|6|7|)'
+  ```
 - A single-character delimiter is now treated as a plain string delimiter rather than a regular expression delimiter, even if it's a regular expression meta-character.
     - This means you can just write `--delimiter '|'` instead of escaping it as `--delimiter '\|'`
 - Bug fixes
diff --git a/man/man1/fzf.1 b/man/man1/fzf.1
index d848d0e9..b237c110 100644
--- a/man/man1/fzf.1
+++ b/man/man1/fzf.1
@@ -242,6 +242,7 @@ color mappings.
     \fBmarker                \fRMulti\-select marker
     \fBspinner               \fRStreaming input indicator
     \fBheader (header\-fg)   \fRHeader
+    \fBnth                   \fRParts of the line specified by \fB\-\-nth\fR (only supports attributes)
 
 .B ANSI COLORS:
     \fB\-1         \fRDefault terminal foreground/background color
diff --git a/src/options.go b/src/options.go
index 87ec9e6f..3dc5d2a6 100644
--- a/src/options.go
+++ b/src/options.go
@@ -1207,6 +1207,8 @@ func parseTheme(defaultTheme *tui.ColorTheme, str string) (*tui.ColorTheme, erro
 				mergeAttr(&theme.SelectedFg)
 			case "selected-bg":
 				mergeAttr(&theme.SelectedBg)
+			case "nth":
+				mergeAttr(&theme.Nth)
 			case "gutter":
 				mergeAttr(&theme.Gutter)
 			case "hl":
@@ -2966,6 +2968,10 @@ func validateOptions(opts *Options) error {
 		}
 	}
 
+	if opts.Theme.Nth.IsColorDefined() {
+		return errors.New("only ANSI attributes are allowed for 'nth' (regular, bold, underline, reverse, dim, italic, strikethrough)")
+	}
+
 	return nil
 }
 
diff --git a/src/result.go b/src/result.go
index f10db19b..ada31d59 100644
--- a/src/result.go
+++ b/src/result.go
@@ -104,11 +104,11 @@ func minRank() Result {
 	return Result{item: &minItem, points: [4]uint16{math.MaxUint16, 0, 0, 0}}
 }
 
-func (result *Result) colorOffsets(matchOffsets []Offset, theme *tui.ColorTheme, colBase tui.ColorPair, colMatch tui.ColorPair, current bool) []colorOffset {
+func (result *Result) colorOffsets(matchOffsets []Offset, nthOffsets []Offset, theme *tui.ColorTheme, colBase tui.ColorPair, colMatch tui.ColorPair, attrNth tui.Attr, current bool) []colorOffset {
 	itemColors := result.item.Colors()
 
 	// No ANSI codes
-	if len(itemColors) == 0 {
+	if len(itemColors) == 0 && len(nthOffsets) == 0 {
 		var offsets []colorOffset
 		for _, off := range matchOffsets {
 			offsets = append(offsets, colorOffset{offset: [2]int32{off[0], off[1]}, color: colMatch, match: true})
@@ -118,7 +118,7 @@ func (result *Result) colorOffsets(matchOffsets []Offset, theme *tui.ColorTheme,
 
 	// Find max column
 	var maxCol int32
-	for _, off := range matchOffsets {
+	for _, off := range append(matchOffsets, nthOffsets...) {
 		if off[1] > maxCol {
 			maxCol = off[1]
 		}
@@ -129,20 +129,33 @@ func (result *Result) colorOffsets(matchOffsets []Offset, theme *tui.ColorTheme,
 		}
 	}
 
-	cols := make([]int, maxCol)
+	type cellInfo struct {
+		index int
+		color bool
+		match bool
+		nth   bool
+	}
+
+	cols := make([]cellInfo, maxCol)
 	for colorIndex, ansi := range itemColors {
 		for i := ansi.offset[0]; i < ansi.offset[1]; i++ {
-			cols[i] = colorIndex + 1 // 1-based index of itemColors
+			cols[i] = cellInfo{colorIndex, true, false, false}
 		}
 	}
 
 	for _, off := range matchOffsets {
 		for i := off[0]; i < off[1]; i++ {
-			// Negative of 1-based index of itemColors
-			// - The extra -1 means highlighted
-			if cols[i] >= 0 {
-				cols[i] = cols[i]*-1 - 1
-			}
+			cols[i].match = true
+		}
+	}
+
+	for _, off := range nthOffsets {
+		// Exclude the whole line
+		if int(off[1])-int(off[0]) == result.item.text.Length() {
+			continue
+		}
+		for i := off[0]; i < off[1]; i++ {
+			cols[i].nth = true
 		}
 	}
 
@@ -152,7 +165,7 @@ func (result *Result) colorOffsets(matchOffsets []Offset, theme *tui.ColorTheme,
 	// ------------  ----  --  ----
 	//   ++++++++      ++++++++++
 	// --++++++++--  --++++++++++---
-	curr := 0
+	var curr cellInfo = cellInfo{0, false, false, false}
 	start := 0
 	ansiToColorPair := func(ansi ansiOffset, base tui.ColorPair) tui.ColorPair {
 		fg := ansi.color.fg
@@ -175,12 +188,12 @@ func (result *Result) colorOffsets(matchOffsets []Offset, theme *tui.ColorTheme,
 	}
 	var colors []colorOffset
 	add := func(idx int) {
-		if curr != 0 && idx > start {
-			if curr < 0 {
+		if (curr.color || curr.nth || curr.match) && idx > start {
+			if curr.match {
 				color := colMatch
 				var url *url
-				if curr < -1 && theme.Colored {
-					ansi := itemColors[-curr-2]
+				if curr.color && theme.Colored {
+					ansi := itemColors[curr.index]
 					url = ansi.color.url
 					origColor := ansiToColorPair(ansi, colMatch)
 					// hl or hl+ only sets the foreground color, so colMatch is the
@@ -197,15 +210,28 @@ func (result *Result) colorOffsets(matchOffsets []Offset, theme *tui.ColorTheme,
 						color = origColor.MergeNonDefault(color)
 					}
 				}
+				if curr.nth {
+					color = color.WithAttr(attrNth)
+				}
 				colors = append(colors, colorOffset{
 					offset: [2]int32{int32(start), int32(idx)}, color: color, match: true, url: url})
-			} else {
-				ansi := itemColors[curr-1]
+			} else if curr.color {
+				ansi := itemColors[curr.index]
+				color := ansiToColorPair(ansi, colBase)
+				if curr.nth {
+					color = color.WithAttr(attrNth)
+				}
 				colors = append(colors, colorOffset{
 					offset: [2]int32{int32(start), int32(idx)},
-					color:  ansiToColorPair(ansi, colBase),
+					color:  color,
 					match:  false,
 					url:    ansi.color.url})
+			} else {
+				colors = append(colors, colorOffset{
+					offset: [2]int32{int32(start), int32(idx)},
+					color:  colBase.WithAttr(attrNth),
+					match:  false,
+					url:    nil})
 			}
 		}
 	}
diff --git a/src/result_test.go b/src/result_test.go
index c11e1ab5..520ee4b1 100644
--- a/src/result_test.go
+++ b/src/result_test.go
@@ -131,7 +131,7 @@ func TestColorOffset(t *testing.T) {
 
 	colBase := tui.NewColorPair(89, 189, tui.AttrUndefined)
 	colMatch := tui.NewColorPair(99, 199, tui.AttrUndefined)
-	colors := item.colorOffsets(offsets, tui.Dark256, colBase, colMatch, true)
+	colors := item.colorOffsets(offsets, nil, tui.Dark256, colBase, colMatch, tui.AttrUndefined, true)
 	assert := func(idx int, b int32, e int32, c tui.ColorPair) {
 		o := colors[idx]
 		if o.offset[0] != b || o.offset[1] != e || o.color != c {
@@ -155,20 +155,30 @@ func TestColorOffset(t *testing.T) {
 
 	colRegular := tui.NewColorPair(-1, -1, tui.AttrUndefined)
 	colUnderline := tui.NewColorPair(-1, -1, tui.Underline)
-	colors = item.colorOffsets(offsets, tui.Dark256, colRegular, colUnderline, true)
 
-	// [{[0 5] {1 5 0}} {[5 15] {1 5 8}} {[15 20] {1 5 0}}
-	//  {[22 25] {2 6 1}} {[25 27] {2 6 9}} {[27 30] {-1 -1 8}}
-	//  {[30 32] {3 7 8}} {[32 33] {-1 -1 8}} {[33 35] {4 8 9}}
-	//  {[35 40] {4 8 1}}]
-	assert(0, 0, 5, tui.NewColorPair(1, 5, tui.AttrUndefined))
-	assert(1, 5, 15, tui.NewColorPair(1, 5, tui.Underline))
-	assert(2, 15, 20, tui.NewColorPair(1, 5, tui.AttrUndefined))
-	assert(3, 22, 25, tui.NewColorPair(2, 6, tui.Bold))
-	assert(4, 25, 27, tui.NewColorPair(2, 6, tui.Bold|tui.Underline))
-	assert(5, 27, 30, colUnderline)
-	assert(6, 30, 32, tui.NewColorPair(3, 7, tui.Underline))
-	assert(7, 32, 33, colUnderline)
-	assert(8, 33, 35, tui.NewColorPair(4, 8, tui.Bold|tui.Underline))
-	assert(9, 35, 40, tui.NewColorPair(4, 8, tui.Bold))
+	nthOffsets := []Offset{{37, 39}, {42, 45}}
+	for _, attr := range []tui.Attr{tui.AttrRegular, tui.StrikeThrough} {
+		colors = item.colorOffsets(offsets, nthOffsets, tui.Dark256, colRegular, colUnderline, attr, true)
+
+		// [{[0 5] {1 5 0}} {[5 15] {1 5 8}} {[15 20] {1 5 0}}
+		//  {[22 25] {2 6 1}} {[25 27] {2 6 9}} {[27 30] {-1 -1 8}}
+		//  {[30 32] {3 7 8}} {[32 33] {-1 -1 8}} {[33 35] {4 8 9}}
+		//  {[35 37] {4 8 1}} {[37 39] {4 8 x|1}} {[39 40] {4 8 x|1}}]
+		assert(0, 0, 5, tui.NewColorPair(1, 5, tui.AttrUndefined))
+		assert(1, 5, 15, tui.NewColorPair(1, 5, tui.Underline))
+		assert(2, 15, 20, tui.NewColorPair(1, 5, tui.AttrUndefined))
+		assert(3, 22, 25, tui.NewColorPair(2, 6, tui.Bold))
+		assert(4, 25, 27, tui.NewColorPair(2, 6, tui.Bold|tui.Underline))
+		assert(5, 27, 30, colUnderline)
+		assert(6, 30, 32, tui.NewColorPair(3, 7, tui.Underline))
+		assert(7, 32, 33, colUnderline)
+		assert(8, 33, 35, tui.NewColorPair(4, 8, tui.Bold|tui.Underline))
+		assert(9, 35, 37, tui.NewColorPair(4, 8, tui.Bold))
+		expected := tui.Bold | attr
+		if attr == tui.AttrRegular {
+			expected = tui.AttrRegular
+		}
+		assert(10, 37, 39, tui.NewColorPair(4, 8, expected))
+		assert(11, 39, 40, tui.NewColorPair(4, 8, tui.Bold))
+	}
 }
diff --git a/src/terminal.go b/src/terminal.go
index 2b86e010..a49fb5e8 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -301,7 +301,9 @@ type Terminal struct {
 	scrollbar          string
 	previewScrollbar   string
 	ansi               bool
+	nthAttr            tui.Attr
 	nth                []Range
+	nthCurrent         []Range
 	tabstop            int
 	margin             [4]sizeSpec
 	padding            [4]sizeSpec
@@ -885,7 +887,9 @@ func NewTerminal(opts *Options, eventBox *util.EventBox, executor *util.Executor
 		header:             []string{},
 		header0:            opts.Header,
 		ansi:               opts.Ansi,
+		nthAttr:            opts.Theme.Nth.Attr,
 		nth:                opts.Nth,
+		nthCurrent:         opts.Nth,
 		tabstop:            opts.Tabstop,
 		hasStartActions:    false,
 		hasResultActions:   false,
@@ -1171,7 +1175,7 @@ func (t *Terminal) ansiLabelPrinter(str string, color *tui.ColorPair, fill bool)
 	printFn := func(window tui.Window, limit int) {
 		if offsets == nil {
 			// tui.Col* are not initialized until renderer.Init()
-			offsets = result.colorOffsets(nil, t.theme, *color, *color, false)
+			offsets = result.colorOffsets(nil, nil, t.theme, *color, *color, t.nthAttr, false)
 		}
 		for limit > 0 {
 			if length > limit {
@@ -2717,7 +2721,22 @@ func (t *Terminal) printHighlighted(result Result, colBase tui.ColorPair, colMat
 		}
 		sort.Sort(ByOrder(charOffsets))
 	}
-	allOffsets := result.colorOffsets(charOffsets, t.theme, colBase, colMatch, current)
+	var nthOffsets []Offset
+	if len(t.nth) > 0 && postTask != nil {
+		var tokens []Token
+		if item.transformed != nil {
+			tokens = item.transformed.tokens
+		} else {
+			tokens = Transform(Tokenize(item.text.ToString(), t.delimiter), t.nthCurrent)
+		}
+		for _, token := range tokens {
+			start := token.prefixLength
+			end := start + int32(token.text.Length())
+			nthOffsets = append(nthOffsets, Offset{int32(start), int32(end)})
+		}
+		sort.Sort(ByOrder(nthOffsets))
+	}
+	allOffsets := result.colorOffsets(charOffsets, nthOffsets, t.theme, colBase, colMatch, t.nthAttr, current)
 
 	maxLines := 1
 	if t.canSpanMultiLines() {
@@ -4667,6 +4686,7 @@ func (t *Terminal) Loop() error {
 					// The default
 					newNth = &t.nth
 				}
+				t.nthCurrent = *newNth
 				// Cycle
 				if len(tokens) > 1 {
 					a.a = strings.Join(append(tokens[1:], tokens[0]), "|")
diff --git a/src/tui/dummy.go b/src/tui/dummy.go
index a49677c6..aaa9a7ea 100644
--- a/src/tui/dummy.go
+++ b/src/tui/dummy.go
@@ -11,6 +11,10 @@ func HasFullscreenRenderer() bool {
 var DefaultBorderShape = BorderRounded
 
 func (a Attr) Merge(b Attr) Attr {
+	if b == AttrRegular {
+		return b
+	}
+
 	return a | b
 }
 
diff --git a/src/tui/tui.go b/src/tui/tui.go
index 0ab4874b..921c7a04 100644
--- a/src/tui/tui.go
+++ b/src/tui/tui.go
@@ -205,6 +205,10 @@ type ColorAttr struct {
 	Attr  Attr
 }
 
+func (a ColorAttr) IsColorDefined() bool {
+	return a.Color != colUndefined
+}
+
 func NewColorAttr() ColorAttr {
 	return ColorAttr{Color: colUndefined, Attr: AttrUndefined}
 }
@@ -305,6 +309,7 @@ type ColorTheme struct {
 	Bg               ColorAttr
 	ListFg           ColorAttr
 	ListBg           ColorAttr
+	Nth              ColorAttr
 	SelectedFg       ColorAttr
 	SelectedBg       ColorAttr
 	SelectedMatch    ColorAttr
@@ -703,6 +708,7 @@ func EmptyTheme() *ColorTheme {
 		HeaderBg:         ColorAttr{colUndefined, AttrUndefined},
 		HeaderBorder:     ColorAttr{colUndefined, AttrUndefined},
 		HeaderLabel:      ColorAttr{colUndefined, AttrUndefined},
+		Nth:              ColorAttr{colUndefined, AttrUndefined},
 	}
 }
 
@@ -746,6 +752,7 @@ func NoColorTheme() *ColorTheme {
 		HeaderBg:         ColorAttr{colDefault, AttrUndefined},
 		HeaderBorder:     ColorAttr{colDefault, AttrUndefined},
 		HeaderLabel:      ColorAttr{colDefault, AttrUndefined},
+		Nth:              ColorAttr{colUndefined, AttrUndefined},
 	}
 }
 
@@ -786,6 +793,7 @@ func init() {
 		InputBg:          ColorAttr{colUndefined, AttrUndefined},
 		InputBorder:      ColorAttr{colUndefined, AttrUndefined},
 		InputLabel:       ColorAttr{colUndefined, AttrUndefined},
+		Nth:              ColorAttr{colUndefined, AttrUndefined},
 	}
 	Dark256 = &ColorTheme{
 		Colored:          true,
@@ -823,6 +831,7 @@ func init() {
 		InputBg:          ColorAttr{colUndefined, AttrUndefined},
 		InputBorder:      ColorAttr{colUndefined, AttrUndefined},
 		InputLabel:       ColorAttr{colUndefined, AttrUndefined},
+		Nth:              ColorAttr{colUndefined, AttrUndefined},
 	}
 	Light256 = &ColorTheme{
 		Colored:          true,
@@ -863,6 +872,7 @@ func init() {
 		HeaderBg:         ColorAttr{colUndefined, AttrUndefined},
 		HeaderBorder:     ColorAttr{colUndefined, AttrUndefined},
 		HeaderLabel:      ColorAttr{colUndefined, AttrUndefined},
+		Nth:              ColorAttr{colUndefined, AttrUndefined},
 	}
 }