From 0b08f0dea076bcc66a2ffe7006e7392d30500f53 Mon Sep 17 00:00:00 2001
From: Junegunn Choi <junegunn.c@gmail.com>
Date: Fri, 6 Mar 2026 19:21:22 +0900
Subject: [PATCH] Fix preview follow/scroll with long wrapped lines

Fixes bugs reported in https://github.com/junegunn/fzf/pull/4703:

* Clamp followOffset return value to avoid going past the end of lines
* Account for t.previewed.filled when determining scrollability
---
 src/terminal.go      |  6 +++---
 test/test_preview.rb | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/src/terminal.go b/src/terminal.go
index 50390de4..59dbb71e 100644
--- a/src/terminal.go
+++ b/src/terminal.go
@@ -4223,7 +4223,7 @@ func (t *Terminal) followOffset() int {
 	for i := len(body) - 1; i >= 0; i-- {
 		h := t.previewLineHeight(body[i], maxWidth)
 		if visualLines+h > height {
-			return headerLines + i + 1
+			return min(len(lines)-1, headerLines+i+1)
 		}
 		visualLines += h
 	}
@@ -4521,7 +4521,7 @@ Loop:
 				}
 			}
 
-			t.previewer.scrollable = t.previewer.scrollable || t.pwindow.Y() == height-1 && t.pwindow.X() == t.pwindow.Width()
+			t.previewer.scrollable = t.previewer.scrollable || t.pwindow.Y() == height-1 && t.pwindow.X() == t.pwindow.Width() || t.previewed.filled
 			if fillRet == tui.FillNextLine {
 				continue
 			} else if fillRet == tui.FillSuspend {
@@ -4544,7 +4544,7 @@ Loop:
 		}
 		lineNo++
 	}
-	t.previewer.scrollable = t.previewer.scrollable || index < len(lines)-1
+	t.previewer.scrollable = t.previewer.scrollable || t.previewed.filled || index < len(lines)-1
 	t.previewed.image = image
 	t.previewed.wireframe = wireframe
 }
diff --git a/test/test_preview.rb b/test/test_preview.rb
index 616074c3..68f3e117 100644
--- a/test/test_preview.rb
+++ b/test/test_preview.rb
@@ -393,6 +393,20 @@ class TestPreview < TestInteractive
     end
   end
 
+  def test_preview_follow_wrap_long_line
+    tmux.send_keys %(seq 1 | #{FZF} --preview "seq 2; yes yes | head -10000 | tr '\n' ' '" --preview-window follow,wrap --bind up:preview-up,down:preview-down), :Enter
+    tmux.until do |lines|
+      assert_equal 1, lines.match_count
+      assert lines.any_include?('3/3 │')
+    end
+    tmux.send_keys :Up
+    tmux.until { |lines| assert lines.any_include?('2/3 │') }
+    tmux.send_keys :Up
+    tmux.until { |lines| assert lines.any_include?('1/3 │') }
+    tmux.send_keys :Down
+    tmux.until { |lines| assert lines.any_include?('2/3 │') }
+  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 }