clamp history cursor in SetCurrent to avoid out-of-bounds panics

Author: dgageot

pkg/history/history.go

@@ -71,9 +71,11 @@ func (h *History) Next() string {
 	return h.Messages[h.current]
 }
 
-// SetCurrent positions the cursor at index i.
+// SetCurrent positions the cursor at index i, clamped to [0, len(Messages)].
+// Keeping the cursor in this range guarantees that subsequent Previous and
+// Next calls never index out of bounds.
 func (h *History) SetCurrent(i int) {
-	h.current = i
+	h.current = max(0, min(i, len(h.Messages)))
 }
 
 // LatestMatch returns the most recent entry that strictly extends prefix, or
@@ -152,7 +154,7 @@ func (h *History) load() error {
 	}
 
 	for line := range bytes.Lines(data) {
-		line = bytes.TrimRight(line, "\n")
+		line = bytes.TrimSuffix(line, []byte("\n"))
 		if len(line) == 0 {
 			continue
 		}

pkg/history/history_test.go

@@ -418,6 +418,36 @@ func TestHistory_SetCurrent(t *testing.T) {
 	assert.Empty(t, h.Next())
 }
 
+func TestHistory_SetCurrentOutOfRange(t *testing.T) {
+	t.Parallel()
+	tmpDir := t.TempDir()
+	h, err := New(tmpDir)
+	require.NoError(t, err)
+
+	require.NoError(t, h.Add("first"))
+	require.NoError(t, h.Add("second"))
+
+	// A negative value clamps to 0; Previous returns the oldest entry.
+	h.SetCurrent(-5)
+	assert.Equal(t, "first", h.Previous())
+
+	// A value past the end clamps to len(Messages); Next returns empty.
+	h.SetCurrent(100)
+	assert.Empty(t, h.Next())
+
+	// And from the clamped position, Previous returns the latest entry.
+	h.SetCurrent(100)
+	assert.Equal(t, "second", h.Previous())
+
+	// On empty history, SetCurrent never causes a panic.
+	empty, err := New(t.TempDir())
+	require.NoError(t, err)
+	empty.SetCurrent(-5)
+	assert.Empty(t, empty.Previous())
+	empty.SetCurrent(100)
+	assert.Empty(t, empty.Next())
+}
+
 func TestHistory_VeryLongMessage(t *testing.T) {
 	tmpDir := t.TempDir()