Fixed deletion checking bug that could cause misreading of the control+r prompt.

internal/reader/changes.go

@@ -78,7 +78,10 @@ func changes(previous, next screen.Snapshot, cursorEcho bool) []presentation.Mes
 	if len(changedRows) == 1 && scrollStart == scrollEnd {
 		row := changedRows[0]
 		before, after := previous.Line(row), next.Line(row)
-		if next.Y == previous.Y && next.Y == row && next.X < previous.X && previous.X-next.X <= 4 && len([]rune(next.Text(row))) < len([]rune(previous.Text(row))) {
+		// A shorter replacement prompt can also move the cursor left. Only
+		// echo removed text when the surrounding text matches a deletion.
+		if next.Y == previous.Y && next.Y == row && next.X < previous.X && previous.X-next.X <= 4 && len([]rune(next.Text(row))) < len([]rune(previous.Text(row))) &&
+			slices.Equal(before[:next.X], after[:next.X]) && strings.TrimRight(string(before[previous.X:]), " ") == strings.TrimRight(string(after[next.X:]), " ") {
 			removed := before[next.X:previous.X]
 			if len(removed) == 1 {
 				return []presentation.Message{presentation.Character_message(removed[0])}

internal/terminal/emulator_linux_test.go

@@ -140,6 +140,27 @@ func TestPTYAlternateScreenResizeAndScroll(t *testing.T) {
 	}
 }
 
+func TestPTYReverseSearchPromptReplacement(t *testing.T) {
+	for _, promptWidth := range []int{2, 23, 24, 25, 26, 40} {
+		t.Run(fmt.Sprint(promptWidth), func(t *testing.T) {
+			emulator, err := new_emulator(3, 80)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer emulator.close()
+			engine := reader.New()
+			emulator.feed([]byte(strings.Repeat("p", promptWidth-2) + "$ "))
+			engine.Update(emulator.snapshot(true, false))
+			// Bash Readline repaints the prompt and clears any remaining tail.
+			searchPrompt := "(reverse-i-search)`': "
+			emulator.feed([]byte("\r" + searchPrompt + "\x1b[K"))
+			if got := engine.Update(emulator.snapshot(true, false)); len(got) != 1 || got[0].Character != nil || strings.TrimRight(got[0].Text, " ") != strings.TrimRight(searchPrompt, " ") {
+				t.Fatalf("search prompt: got %+v, want %q", got, searchPrompt)
+			}
+		})
+	}
+}
+
 func TestPTYCarriageReturnEraseAndCursorEcho(t *testing.T) {
 	emulator, err := new_emulator(3, 20)
 	if err != nil {