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LAB-1803: Trim styled blanks in vt scrollback #15

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LAB-1803: Trim styled blanks in vt scrollback #15

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7112e45
LAB-1803: Cover styled blank scrollback trimming
May 13, 2026
fc372e8
LAB-1803: Trim trailing styled blanks in vt scrollback
May 13, 2026
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16 changes: 14 additions & 2 deletions vt/scrollback.go
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Original file line number Diff line number Diff line change
Expand Up @@ -115,12 +115,24 @@ func (s *Scrollback) CellAt(x, y int) *uv.Cell {
func trimTrailingEmptyCells(line uv.Line) uv.Line {
lastNonEmpty := -1
for i := len(line) - 1; i >= 0; i-- {
c := &line[i]
if !c.IsZero() && !c.Equal(&uv.EmptyCell) {
if !isTrailingScrollbackBlank(&line[i]) {
lastNonEmpty = i
break
}
}

return line[:lastNonEmpty+1]
}

func isTrailingScrollbackBlank(cell *uv.Cell) bool {
if cell == nil {
return true
}
if cell.IsZero() || cell.Equal(&uv.EmptyCell) {
Comment on lines +127 to +131

@greptile-apps greptile-apps Bot May 13, 2026

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P2 The nil check here is dead code. isTrailingScrollbackBlank is only ever called with &line[i] inside trimTrailingEmptyCells, where i is a valid slice index, so the pointer is always non-nil. The branch can be removed without any behavioural change.

Suggested change
func isTrailingScrollbackBlank(cell *uv.Cell) bool {
if cell == nil {
return true
}
if cell.IsZero() || cell.Equal(&uv.EmptyCell) {
func isTrailingScrollbackBlank(cell *uv.Cell) bool {
if cell.IsZero() || cell.Equal(&uv.EmptyCell) {

return true
}
Comment on lines +126 to +133

@greptile-apps greptile-apps Bot May 13, 2026

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P2 Width == 0 guard silently unreachable for zero-value continuation cells

The PR description states "Preserve width-0 continuation cells so wide-character layout state is not discarded," but a zero-value continuation cell (Width: 0, Content: "", Style: {}) satisfies IsZero() and returns true before the Width == 0 guard is ever reached. Only a non-zero continuation cell (e.g. one carrying inherited style) is actually protected. A trailing zero-value continuation cell was already trimmed before this PR, so there is no regression, but the protection is narrower than the PR description implies. Worth a clarifying code comment if zero-value continuations at trailing positions are expected to be preserved too.

if cell.Width == 0 {
return false
}
return cell.Content == "" || cell.Content == " "
}
27 changes: 27 additions & 0 deletions vt/scrollback_test.go
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Original file line number Diff line number Diff line change
@@ -1,7 +1,10 @@
package vt

import (
"image/color"
"testing"

uv "github.com/charmbracelet/ultraviolet"
)

func TestScrollback(t *testing.T) {
Expand Down Expand Up @@ -68,6 +71,30 @@ func TestScrollback(t *testing.T) {
}
})

t.Run("trims trailing styled blanks", func(t *testing.T) {
sb := NewScrollback(1)
line := make(uv.Line, 12)
for i := range line {
line[i] = uv.Cell{
Content: " ",
Style: uv.Style{Bg: color.RGBA{R: 24, G: 28, B: 36, A: 255}},
Width: 1,
}
}
for i, r := range "prompt" {
line[i] = uv.Cell{Content: string(r), Width: 1}
}

sb.Push(line)

if got := len(sb.Line(0)); got != len("prompt") {
t.Fatalf("stored line length = %d, want %d", got, len("prompt"))
}
if got := sb.Line(0).String(); got != "prompt" {
t.Fatalf("stored line text = %q, want %q", got, "prompt")
}
})

t.Run("clear scrollback", func(t *testing.T) {
e := NewEmulator(20, 5)

Expand Down
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