Long lines get silently truncated in the diff viewer

[fgrehm]

What's happening

Any diff line longer than the viewport width gets cut off with no way to see the rest. No horizontal scrolling, no wrapping -- the content is just gone.

Weird thing is it happens in two places:

1. delta is called with --max-line-length=<width>, so it clips before output even arrives.
   

   diffnav/pkg/ui/panes/diffviewer/diffviewer.go

   Lines 282 to 294 in 2898ff7

   	useSideBySide := sideBySide && !file.IsNew && !file.IsDelete
   	args := []string{
   	"--paging=never",
   	fmt.Sprintf("-w=%d", width),
   	fmt.Sprintf("--max-line-length=%d", width),
   	}
   	if useSideBySide {
   	args = append(args, "--side-by-side")
   	}
   	deltac := exec.Command("delta", args...)
   	deltac.Env = os.Environ()
   	deltac.Stdin = strings.NewReader(file.String() + "\n")
   	out, err := deltac.Output()

2. Then there's a post-processing pass that truncates anything still wider than the viewport
   

   diffnav/pkg/ui/panes/diffviewer/diffviewer.go

   Lines 82 to 95 in 2898ff7

   	case diffContentMsg:
   	// Truncate lines to viewport width to prevent ANSI escape overflow.
   	lines := strings.Split(msg.text, "\n")
   	for i, line := range lines {
   	if lipgloss.Width(line) > m.vp.Width() && m.vp.Width() > 0 {
   	lines[i] = ansi.Truncate(line, m.vp.Width(), "")
   	}
   	}
   	diff := strings.Join(lines, "\n")
   	if _, ok := m.cache[msg.cacheKey]; ok {
   	m.cache[msg.cacheKey].diff = diff
   	}
   	m.vp.SetContent(diff)
   	}

(The comment there says "to prevent ANSI escape overflow", so I get why it's there but the result is you can't read long lines at all 😬 )

To reproduce

Just use any diff with long lines and / or narrow your terminal a bit and the content just disappears at the right edge.

What I'd expect

Either:

• word wraping: long lines continue on the next visual line (could use muesli/reflow/wrap which is already in go.mod)
• or horizontal scrolling: left/right keybinds to pan the viewport

Happy to put up a PR if you have a preference on the approach 🚀

[dlvhdr]

Does delta not have an option to handle wrapping? If not then we should probably do horizontal scrolling

[fgrehm]

Does delta not have an option to handle wrapping? If not then we should probably do horizontal scrolling

Apparently it does!

Haven't checked the CLI flags and whatnot but can poke around and try putting up a PR for this later today if you feel like we should just go down that path.