Fix --preview-window follow not working correctly with wrapping

Fix #3243
Fix #4258

CHANGELOG.md

@@ -36,6 +36,7 @@ CHANGELOG
 - Added fish completion support (#4605) (@lalvarezt)
 - zsh: Handle multi-line history selection (#4595) (@LangLangBart)
 - Bug fixes
+    - Fixed `--preview-window follow` not working correctly with wrapping (#3243, #4258)
     - Fixed symlinks to directories being returned as files (#4676) (@skk64)
     - Fixed SIGHUP signal handling (#4668) (@LangLangBart)
     - Fixed preview process not killed on exit (#4667)

src/terminal.go

@@ -4093,6 +4093,80 @@ func extractPassThroughs(line string) ([]string, string) {
 	return passThroughs, transformed
 }
 
+// followOffset computes the correct content-line offset for follow mode,
+// accounting for line wrapping in the preview window.
+func (t *Terminal) followOffset() int {
+	lines := t.previewer.lines
+	headerLines := t.activePreviewOpts.headerLines
+	height := t.pwindow.Height() - headerLines
+	if height <= 0 || len(lines) <= headerLines {
+		return headerLines
+	}
+
+	body := lines[headerLines:]
+	if !t.activePreviewOpts.wrap {
+		return max(t.previewer.offset, headerLines+len(body)-height)
+	}
+
+	maxWidth := t.pwindow.Width()
+	visualLines := 0
+	for i := len(body) - 1; i >= 0; i-- {
+		h := t.previewLineHeight(body[i], maxWidth)
+		if visualLines+h > height {
+			return headerLines + i + 1
+		}
+		visualLines += h
+	}
+	return headerLines
+}
+
+// previewLineHeight estimates the number of visual lines a preview content line
+// occupies when wrapping is enabled.
+func (t *Terminal) previewLineHeight(line string, maxWidth int) int {
+	if maxWidth <= 0 {
+		return 1
+	}
+
+	// For word-wrap mode, count the sub-lines produced by word wrapping.
+	// Each sub-line may still char-wrap if it contains a word longer than the width.
+	if t.activePreviewOpts.wrapWord {
+		subLines := t.wordWrapAnsiLine(line, maxWidth, t.wrapSignWidth)
+		total := 0
+		for i, sub := range subLines {
+			prefixWidth := 0
+			cols := maxWidth
+			if i > 0 {
+				prefixWidth = t.wrapSignWidth
+				cols -= t.wrapSignWidth
+			}
+			w := t.ansiLineWidth(sub, prefixWidth)
+			if cols <= 0 {
+				cols = 1
+			}
+			total += max(1, (w+cols-1)/cols)
+		}
+		return total
+	}
+
+	// For char-wrap, compute visible width and divide by available width.
+	w := t.ansiLineWidth(line, 0)
+	if w <= maxWidth {
+		return 1
+	}
+	remaining := w - maxWidth
+	contWidth := max(1, maxWidth-t.wrapSignWidth)
+	return 1 + (remaining+contWidth-1)/contWidth
+}
+
+// ansiLineWidth computes the display width of a string, skipping ANSI escape sequences.
+// prefixWidth is the visual offset where the content starts (e.g. wrap sign width for
+// continuation lines), used for correct tab stop alignment.
+func (t *Terminal) ansiLineWidth(line string, prefixWidth int) int {
+	trimmed, _, _ := extractColor(line, nil, nil)
+	_, width := t.processTabs([]rune(trimmed), prefixWidth)
+	return width - prefixWidth
+}
+
 func (t *Terminal) wordWrapAnsiLine(line string, maxWidth int, wrapSignWidth int) []string {
 	if maxWidth <= 0 {
 		return []string{line}
@@ -5704,7 +5778,7 @@ func (t *Terminal) Loop() error {
 						t.previewer.lines = result.lines
 						t.previewer.spinner = result.spinner
 						if t.hasPreviewWindow() && t.previewer.following.Enabled() {
-							t.previewer.offset = max(t.previewer.offset, len(t.previewer.lines)-(t.pwindow.Height()-t.activePreviewOpts.headerLines))
+							t.previewer.offset = t.followOffset()
 						} else if result.offset >= 0 {
 							t.previewer.offset = util.Constrain(result.offset, t.activePreviewOpts.headerLines, len(t.previewer.lines)-1)
 						}

src/tui/light.go

@@ -1423,8 +1423,10 @@ func (w *LightWindow) fill(str string, resetCode string) FillReturn {
 	for i, line := range allLines {
 		lines := WrapLine(line, w.posx, w.width, w.tabstop, w.wrapSignWidth)
 		for j, wl := range lines {
-			w.stderrInternal(wl.Text, false, resetCode)
-			w.posx += wl.DisplayWidth
+			if w.posx < w.width {
+				w.stderrInternal(wl.Text, false, resetCode)
+				w.posx += wl.DisplayWidth
+			}
 
 			// Wrap line
 			if j < len(lines)-1 || i < len(allLines)-1 {

src/tui/tcell.go

@@ -971,7 +971,9 @@ func (w *TcellWindow) fillString(text string, pair ColorPair) FillReturn {
 					w.renderWrapSign(style)
 				}
 			}
-			w.renderGraphemes(wl.Text, style)
+			if w.lastX < w.width {
+				w.renderGraphemes(wl.Text, style)
+			}
 		}
 	}
 	if w.lastX >= w.width {

src/tui/tui.go

@@ -1377,7 +1377,8 @@ func WrapLine(input string, prefixLength int, initialMax int, tabstop int, wrapS
 	width := 0
 	line := ""
 	gr := uniseg.NewGraphemes(input)
-	max := initialMax
+	maxWidth := initialMax
+	contMax := max(1, initialMax-wrapSignWidth)
 	for gr.Next() {
 		rs := gr.Runes()
 		str := string(rs)
@@ -1392,14 +1393,14 @@ func WrapLine(input string, prefixLength int, initialMax int, tabstop int, wrapS
 		}
 		width += w
 
-		if prefixLength+width <= max {
+		if prefixLength+width <= maxWidth {
 			line += str
 		} else {
 			lines = append(lines, WrappedLine{string(line), width - w})
 			line = str
 			prefixLength = 0
 			width = w
-			max = initialMax - wrapSignWidth
+			maxWidth = contMax
 		}
 	}
 	lines = append(lines, WrappedLine{string(line), width})

test/test_preview.rb

@@ -383,6 +383,16 @@ class TestPreview < TestInteractive
     end
   end
 
+  def test_preview_follow_wrap
+    tmux.send_keys "seq 1 | #{FZF} --preview 'seq 1000' --preview-window right,2,follow,wrap", :Enter
+    tmux.until { |lines| assert_equal 1, lines.match_count }
+    tmux.until do |lines|
+      assert_includes lines[-4], '│ 10 │'
+      assert_includes lines[-3], '│ ↳  │'
+      assert_includes lines[-2], '│ ↳  │'
+    end
+  end
+
   def test_close
     tmux.send_keys "seq 100 | #{FZF} --preview 'echo foo' --bind ctrl-c:close", :Enter
     tmux.until { |lines| assert_equal 100, lines.match_count }
@@ -541,7 +551,7 @@ class TestPreview < TestInteractive
     tmux.send_keys "seq 10 | #{FZF} --preview-border rounded --preview-window '~5,2,+0,<100000(~0,+100,wrap,noinfo)' --preview 'seq 1000'", :Enter
     tmux.until { |lines| assert_equal 10, lines.match_count }
     tmux.until do |lines|
-      assert_equal ['╭────╮', '│ 10 │', '│ ↳ 0│', '│ 10 │', '│ ↳ 1│'], lines.take(5).map(&:strip)
+      assert_equal ['╭────╮', '│ 10 │', '│ ↳  │', '│ 10 │', '│ ↳  │'], lines.take(5).map(&:strip)
     end
   end