ui/termstatus: simplify status tracking

internal/ui/termstatus/status.go

@@ -26,7 +26,7 @@ type Terminal struct {
 	errWriter        io.Writer
 	msg              chan message
 	status           chan status
-	lastStatusLen    int
+	lastStatus       []string
 	inputIsTerminal  bool
 	outputIsTerminal bool
 	canUpdateStatus  bool
@@ -219,12 +219,11 @@ func findUnchangedLines(curr, last []string) []bool {
 // run listens on the channels and updates the terminal screen.
 func (t *Terminal) run(ctx context.Context) {
 	var status []string
-	var lastWrittenStatus []string
 	for {
 		select {
 		case <-ctx.Done():
 			if !terminal.IsProcessBackground(t.fd) {
-				t.writeStatus([]string{}, nil)
+				t.writeStatus([]string{}, false)
 			}
 
 			return
@@ -255,8 +254,7 @@ func (t *Terminal) run(ctx context.Context) {
 				continue
 			}
 
-			t.writeStatus(status, nil)
-			lastWrittenStatus = append([]string{}, status...)
+			t.writeStatus(status, false)
 		case stat := <-t.status:
 			status = append(status[:0], stat.lines...)
 
@@ -265,28 +263,29 @@ func (t *Terminal) run(ctx context.Context) {
 				continue
 			}
 
-			if !slices.Equal(status, lastWrittenStatus) {
-				unchangedLines := findUnchangedLines(status, lastWrittenStatus)
-				t.writeStatus(status, unchangedLines)
-				// Copy the status slice to avoid aliasing
-				lastWrittenStatus = append([]string{}, status...)
-			}
+			t.writeStatus(status, true)
 		}
 	}
 }
 
-func (t *Terminal) writeStatus(status []string, unchanged []bool) {
-	statusLen := len(status)
-	status = append([]string{}, status...)
-	for i := len(status); i < t.lastStatusLen; i++ {
-		// clear no longer used status lines
-		status = append(status, "")
-		if i > 0 {
-			// all lines except the last one must have a line break
-			status[i-1] = status[i-1] + "\n"
+func (t *Terminal) writeStatus(status []string, skipUnchanged bool) {
+	var unchanged []bool
+	if skipUnchanged {
+		if slices.Equal(status, t.lastStatus) {
+			return
 		}
+		unchanged = findUnchangedLines(status, t.lastStatus)
+	}
+
+	lastStatusLen := len(t.lastStatus)
+	// Copy the status slice to avoid aliasing
+	t.lastStatus = append([]string{}, status...)
+
+	// Extend to clear no longer used status lines
+	status = append([]string{}, status...)
+	for i := len(status); i < lastStatusLen; i++ {
+		status = append(status, "")
 	}
-	t.lastStatusLen = statusLen
 
 	for i, line := range status {
 		if unchanged != nil && i < len(unchanged) && unchanged[i] {
@@ -308,6 +307,13 @@ func (t *Terminal) writeStatus(status []string, unchanged []bool) {
 		if err != nil {
 			_, _ = fmt.Fprintf(t.errWriter, "write failed: %v\n", err)
 		}
+		// all lines except the last one must be followed by a line break
+		if i < len(status)-1 {
+			_, err := t.wr.Write([]byte("\n"))
+			if err != nil {
+				_, _ = fmt.Fprintf(t.errWriter, "write failed: %v\n", err)
+			}
+		}
 	}
 
 	if len(status) > 0 {
@@ -400,9 +406,6 @@ func sanitizeLines(lines []string, width int) []string {
 		if width > 0 {
 			line = ui.Truncate(line, width-2)
 		}
-		if i < len(lines)-1 { // Last line gets no line break.
-			line += "\n"
-		}
 		lines[i] = line
 	}
 	return lines

internal/ui/termstatus/status_test.go

@@ -91,8 +91,8 @@ func TestSanitizeLines(t *testing.T) {
 	}{
 		{[]string{""}, 80, []string{""}},
 		{[]string{"too long test line"}, 10, []string{"too long"}},
-		{[]string{"too long test line", "text"}, 10, []string{"too long\n", "text"}},
-		{[]string{"too long test line", "second long test line"}, 10, []string{"too long\n", "second l"}},
+		{[]string{"too long test line", "text"}, 10, []string{"too long", "text"}},
+		{[]string{"too long test line", "second long test line"}, 10, []string{"too long", "second l"}},
 	}
 
 	for _, test := range tests {