Handle cut off lines on Windows

Before this change, on Windows, the rightmost column of the screen would
be cut off and not visible.

With this change in place, that column should now be visible.

Fixes #250.

Ref:
microsoft/terminal#18115 (comment)

twin/screen.go

@@ -684,8 +684,9 @@ func withoutHiddenRunes(runes []StyledRune) []StyledRune {
 }
 
 // Returns the rendered line, plus how many information carrying cells went into
-// it
-func renderLine(row []StyledRune, terminalColorCount ColorCount) (string, int) {
+// it. The width is used to decide whether or not to clear to EOL at the end of
+// the line.
+func renderLine(row []StyledRune, width int, terminalColorCount ColorCount) (string, int) {
 	row = withoutHiddenRunes(row)
 
 	// Strip trailing whitespace
@@ -727,24 +728,30 @@ func renderLine(row []StyledRune, terminalColorCount ColorCount) (string, int) {
 		builder.WriteRune(runeToWrite)
 	}
 
-	// Clear to end of line
-	// https://en.wikipedia.org/wiki/ANSI_escape_code#CSI_(Control_Sequence_Introducer)_sequences
-	builder.WriteString(StyleDefault.RenderUpdateFrom(lastStyle, terminalColorCount))
-	builder.WriteString("\x1b[K")
+	if len(row) < width {
+		// Clear to end of line
+		// https://en.wikipedia.org/wiki/ANSI_escape_code#CSI_(Control_Sequence_Introducer)_sequences
+		//
+		// Note that we can't do this if we're one the last screen column:
+		// https://github.com/microsoft/terminal/issues/18115#issuecomment-2448054645
+		builder.WriteString(StyleDefault.RenderUpdateFrom(lastStyle, terminalColorCount))
+		builder.WriteString("\x1b[K")
+	}
 
 	return builder.String(), len(row)
 }
 
 func (screen *UnixScreen) Show() {
-	_, height := screen.Size()
-	screen.showNLines(height, true)
+	width, height := screen.Size()
+	screen.showNLines(width, height, true)
 }
 
 func (screen *UnixScreen) ShowNLines(height int) {
-	screen.showNLines(height, false)
+	width, _ := screen.Size()
+	screen.showNLines(width, height, false)
 }
 
-func (screen *UnixScreen) showNLines(height int, clearFirst bool) {
+func (screen *UnixScreen) showNLines(width int, height int, clearFirst bool) {
 	var builder strings.Builder
 
 	if clearFirst {
@@ -754,7 +761,7 @@ func (screen *UnixScreen) showNLines(height int, clearFirst bool) {
 	}
 
 	for row := 0; row < height; row++ {
-		rendered, lineLength := renderLine(screen.cells[row], screen.terminalColorCount)
+		rendered, lineLength := renderLine(screen.cells[row], width, screen.terminalColorCount)
 		builder.WriteString(rendered)
 
 		wasLastLine := row == (height - 1)

twin/screen_test.go

@@ -65,7 +65,7 @@ func TestRenderLine(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 2)
 	reset := ""
 	reversed := ""
@@ -80,7 +80,7 @@ func TestRenderLine(t *testing.T) {
 func TestRenderLineEmpty(t *testing.T) {
 	row := []StyledRune{}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 0)
 
 	// All lines are expected to stand on their own, so we always need to clear
@@ -96,7 +96,7 @@ func TestRenderLineLastReversed(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	reversed := ""
@@ -114,7 +114,7 @@ func TestRenderLineLastNonSpace(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	clearToEol := ""
@@ -135,7 +135,7 @@ func TestRenderLineLastReversedPlusTrailingSpace(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	reversed := ""
@@ -157,7 +157,7 @@ func TestRenderLineOnlyTrailingSpaces(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 0)
 
 	// All lines are expected to stand on their own, so we always need to clear
@@ -173,7 +173,7 @@ func TestRenderLineLastReversedSpaces(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	reversed := ""
@@ -190,7 +190,7 @@ func TestRenderLineNonPrintable(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 1)
 	reset := ""
 	white := ""
@@ -211,7 +211,7 @@ func TestRenderHyperlinkAtEndOfLine(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 1)
 
 	assert.Equal(t,
@@ -236,14 +236,39 @@ func TestMultiCharHyperlink(t *testing.T) {
 		},
 	}
 
-	rendered, count := renderLine(row, ColorCount16)
+	rendered, count := renderLine(row, 33, ColorCount16)
 	assert.Equal(t, count, 3)
 
 	assert.Equal(t,
 		strings.ReplaceAll(rendered, "", "ESC"),
 		`ESC[mESC]8;;`+url+`ESC\-X-ESC]8;;ESC\ESC[K`)
 }
 
+func TestRenderLineFullWidth(t *testing.T) {
+	row := []StyledRune{
+		{
+			Rune: 'x',
+		},
+		{
+			Rune: 'y',
+		},
+	}
+
+	rendered, count := renderLine(row, 2, ColorCount16)
+	assert.Equal(t, count, 2)
+
+	assert.Equal(t,
+		strings.ReplaceAll(rendered, "", "ESC"),
+		"ESC[mxy", "Expected no clear-to-EOL at the end of a full-width line")
+
+	rendered, count = renderLine(row, 3, ColorCount16)
+	assert.Equal(t, count, 2)
+
+	assert.Equal(t,
+		strings.ReplaceAll(rendered, "", "ESC"),
+		"ESC[mxyESC[K", "Expected clear-to-EOL at the end of a full-width line")
+}
+
 // Test the most basic form of interruptability. Interrupting and sending a byte
 // should make the reader return EOF.
 //