fix(tui): the Brokers tab keeps its cursor on a broker when a refresh returns fewer

cli/tui/brokers.go

@@ -46,6 +46,11 @@ func (m brokersModel) Update(msg tea.Msg) (brokersModel, tea.Cmd) {
 		m.loading = false
 		m.info = msg.info
 		m.err = msg.err
+		// A broker gone since the last refresh left the cursor past the end,
+		// and View panicked indexing it.
+		if m.info != nil && m.cursor >= len(m.info.Brokers) {
+			m.cursor = max(0, len(m.info.Brokers)-1)
+		}
 	case tea.KeyMsg:
 		if m.info == nil {
 			break

cli/tui/brokers_test.go

@@ -0,0 +1,36 @@
+package tui
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/bmscomp/kates/cli/client"
+)
+
+// The cursor on the last broker, and a refresh with one broker fewer: View
+// indexed past the end and the dashboard died with the broker.
+func TestBrokersRefreshWithFewerBrokers(t *testing.T) {
+	brokers := func(n int) *client.ClusterInfo {
+		info := &client.ClusterInfo{ClusterID: "c1", BrokerCount: n}
+		for i := range n {
+			info.Brokers = append(info.Brokers, client.BrokerNode{ID: i, Host: "kafka", Port: 9092})
+		}
+		return info
+	}
+	m := brokersModel{width: 120, height: 40}
+	m, _ = m.Update(brokersLoadedMsg{info: brokers(3)})
+	m.cursor = 2
+
+	m, _ = m.Update(brokersLoadedMsg{info: brokers(2)})
+	if m.cursor != 1 {
+		t.Errorf("cursor = %d after the refresh, want 1, the last broker", m.cursor)
+	}
+	if view := m.View(); !strings.Contains(view, "Broker 1") {
+		t.Errorf("the view does not show broker 1:\n%s", view)
+	}
+
+	m, _ = m.Update(brokersLoadedMsg{info: brokers(0)})
+	if m.cursor != 0 || !strings.Contains(m.View(), "No brokers found") {
+		t.Errorf("cursor = %d with no brokers, want 0 and the empty view", m.cursor)
+	}
+}