Merge pull request #102 from bnema/fix/reflow-stale-soft-boundary

fix(vt): sever stale soft wrap boundaries on erase

commit: 0214273e2149937dc721c69de427d6b50f118f03
author: bnema · 3mo ago · 2026-07-17 06:22 UTC
committer: GitHub · 3mo ago · 2026-07-17 06:22 UTC
merge of: 239bcd7 + 83a3e26 · diff against the first parent
signature: GPG UnverifiedB5690EEEBB952194 The key is unknown

2 files · +36 -3

M pkg/vt/buffer.go +7 -1


@@ -76,8 +76,14 @@ func (b *buffer) clear(y, x0, x1 int) {
76	76		return
77	77		}
78	78		b.content(y, x1)
	79	+	if x1 >= b.frame.Width {
	80	+	// Erasing through the right edge leaves nothing flowing onto the next
	81	+	// row: the logical line ends here. Keeping a stale soft link would let
	82	+	// reflow merge a repainted row with the unrelated row below it.
	83	+	b.boundaries[y].soft = false
	84	+	}
79	85		if x0 == 0 && x1 >= b.frame.Width {
80		-	b.boundaries[y] = lineBoundary{soft: b.boundaries[y].soft}
	86	+	b.boundaries[y] = lineBoundary{}
81	87		}
82	88		}
83	89

 		return
 	}
 	b.content(y, x1)
+	if x1 >= b.frame.Width {
+		// Erasing through the right edge leaves nothing flowing onto the next
+		// row: the logical line ends here. Keeping a stale soft link would let
+		// reflow merge a repainted row with the unrelated row below it.
+		b.boundaries[y].soft = false
+	}
 	if x0 == 0 && x1 >= b.frame.Width {
-		b.boundaries[y] = lineBoundary{soft: b.boundaries[y].soft}
+		b.boundaries[y] = lineBoundary{}
 	}
 }

M pkg/vt/screen_resize_test.go +29 -2


@@ -121,18 +121,45 @@ func TestResize(t *testing.T) {
121	121		},
122	122		},
123	123		{
124		-	name: "erase preserves a soft wrap boundary",
	124	+	name: "erase severs a soft wrap boundary",
125	125		run: func(t *testing.T) {
126	126		s := NewScreen(4, 2)
127	127		s.Write([]byte("abcdef"))
128	128		s.Write([]byte("\x1b[1;1H\x1b[2K"))
129	129
	130	+	// Erasing through the right edge ends the logical line: the
	131	+	// blank head must not pull "ef" up a row on reflow.
130	132		s.Resize(3, 2)
131		-	if got := rowString(s, 0); got != "ef " {
	133	+	if got := []string{rowString(s, 0), rowString(s, 1)}; strings.Join(got, ",") != " ,ef " {
132	134		t.Fatalf("erased soft line reflow = %q", got)
133	135		}
134	136		},
135	137		},
	138	+	{
	139	+	name: "in-place repaint does not merge with the row below",
	140	+	run: func(t *testing.T) {
	141	+	// Status UIs (docker buildx, shell prompt redraws) repaint a
	142	+	// previously soft-wrapped row with CUP + text + EL and no
	143	+	// newline. The stale soft link must not glue the repainted row
	144	+	// to the unrelated row below: reflow would merge them, and the
	145	+	// next shrink would truncate the merged line, losing cells.
	146	+	s := NewScreen(40, 8)
	147	+	s.Write([]byte(strings.Repeat("A", 40) + "BBBB\r\n"))
	148	+	s.Write([]byte("tail-line\r\n"))
	149	+	s.Write([]byte("\x1b[1;1HSHORT\x1b[K"))
	150	+	s.Write([]byte("\x1b[4;1H"))
	151	+
	152	+	s.Resize(60, 8)
	153	+	if got := []string{rowString(s, 0), rowString(s, 1), rowString(s, 2)}; strings.TrimRight(got[0], " ") != "SHORT" \|\| strings.TrimRight(got[1], " ") != "BBBB" \|\| strings.TrimRight(got[2], " ") != "tail-line" {
	154	+	t.Fatalf("grow rows = %q", got)
	155	+	}
	156	+
	157	+	s.Resize(40, 8)
	158	+	if got := []string{rowString(s, 0), rowString(s, 1), rowString(s, 2)}; strings.TrimRight(got[0], " ") != "SHORT" \|\| strings.TrimRight(got[1], " ") != "BBBB" \|\| strings.TrimRight(got[2], " ") != "tail-line" {
	159	+	t.Fatalf("round-trip rows = %q", got)
	160	+	}
	161	+	},
	162	+	},
136	163		{
137	164		name: "wide edge padding does not become logical content",
138	165		run: func(t *testing.T) {


@@ -121,18 +121,45 @@ func TestResize(t *testing.T) {
121		},	121		},
122		},	122		},
123		{	123		{
124	-	name: "erase preserves a soft wrap boundary",	124	+	name: "erase severs a soft wrap boundary",
125		run: func(t *testing.T) {	125		run: func(t *testing.T) {
126		s := NewScreen(4, 2)	126		s := NewScreen(4, 2)
127		s.Write([]byte("abcdef"))	127		s.Write([]byte("abcdef"))
128		s.Write([]byte("\x1b[1;1H\x1b[2K"))	128		s.Write([]byte("\x1b[1;1H\x1b[2K"))
129			129
			130	+	// Erasing through the right edge ends the logical line: the
			131	+	// blank head must not pull "ef" up a row on reflow.
130		s.Resize(3, 2)	132		s.Resize(3, 2)
131	-	if got := rowString(s, 0); got != "ef " {	133	+	if got := []string{rowString(s, 0), rowString(s, 1)}; strings.Join(got, ",") != " ,ef " {
132		t.Fatalf("erased soft line reflow = %q", got)	134		t.Fatalf("erased soft line reflow = %q", got)
133		}	135		}
134		},	136		},
135		},	137		},
			138	+	{
			139	+	name: "in-place repaint does not merge with the row below",
			140	+	run: func(t *testing.T) {
			141	+	// Status UIs (docker buildx, shell prompt redraws) repaint a
			142	+	// previously soft-wrapped row with CUP + text + EL and no
			143	+	// newline. The stale soft link must not glue the repainted row
			144	+	// to the unrelated row below: reflow would merge them, and the
			145	+	// next shrink would truncate the merged line, losing cells.
			146	+	s := NewScreen(40, 8)
			147	+	s.Write([]byte(strings.Repeat("A", 40) + "BBBB\r\n"))
			148	+	s.Write([]byte("tail-line\r\n"))
			149	+	s.Write([]byte("\x1b[1;1HSHORT\x1b[K"))
			150	+	s.Write([]byte("\x1b[4;1H"))
			151	+
			152	+	s.Resize(60, 8)
			153	+	if got := []string{rowString(s, 0), rowString(s, 1), rowString(s, 2)}; strings.TrimRight(got[0], " ") != "SHORT" \|\| strings.TrimRight(got[1], " ") != "BBBB" \|\| strings.TrimRight(got[2], " ") != "tail-line" {
			154	+	t.Fatalf("grow rows = %q", got)
			155	+	}
			156	+
			157	+	s.Resize(40, 8)
			158	+	if got := []string{rowString(s, 0), rowString(s, 1), rowString(s, 2)}; strings.TrimRight(got[0], " ") != "SHORT" \|\| strings.TrimRight(got[1], " ") != "BBBB" \|\| strings.TrimRight(got[2], " ") != "tail-line" {
			159	+	t.Fatalf("round-trip rows = %q", got)
			160	+	}
			161	+	},
			162	+	},
136		{	163		{
137		name: "wide edge padding does not become logical content",	164		name: "wide edge padding does not become logical content",
138		run: func(t *testing.T) {	165		run: func(t *testing.T) {