Support the mouse in the branch popup

A click on a branch switches to it, the wheel moves the selection, a click
outside closes the popup. The popup is hit-tested by its own position, as it
is drawn after zone.Scan.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/tui/app.go

@@ -244,7 +244,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 
 	case tea.MouseMsg:
 		if m.picker != nil {
-			return m, nil
+			return m.mousePicker(msg)
 		}
 		m.tree.Update(msg)
 		return m, nil
@@ -563,7 +563,9 @@ func (m Model) View() string {
 	}
 	view := zone.Scan(lipgloss.JoinVertical(lipgloss.Left, append(parts, m.footer.View())...))
 	if m.picker != nil { // after zone.Scan, so no zone marker is cut
-		view = overlay(view, m.picker.View(m.width, m.height), m.width, m.height, theme.Fg(m.theme.Backdrop))
+		pop := m.picker.View(m.width, m.height)
+		x, y := m.picker.Origin(m.width, m.height)
+		view = overlay(view, pop, x, y, theme.Fg(m.theme.Backdrop))
 	}
 	return view
 }

internal/tui/branches/branches.go

@@ -35,6 +35,7 @@ type Model struct {
 	loading bool
 	err     error
 	spinner string
+	w, h    int // size of the popup as last rendered, for hit tests
 }
 
 // New returns a picker in the loading state.
@@ -177,11 +178,40 @@ func (m *Model) View(termWidth, termHeight int) string {
 	lines = append(lines, body[:m.rows]...)
 	lines = append(lines, muted.Render(ansi.Truncate("↑↓ select · enter switch · esc cancel", inner, "…")))
 
-	return lipgloss.NewStyle().
+	out := lipgloss.NewStyle().
 		Border(lipgloss.RoundedBorder()).
 		BorderForeground(m.theme.Border).
 		Padding(0, 1).
 		Render(strings.Join(lines, "\n"))
+	m.w, m.h = lipgloss.Width(out), lipgloss.Height(out)
+	return out
+}
+
+// Origin is the top-left cell of the popup, centered in a terminal of the
+// given size. Valid after View.
+func (m *Model) Origin(termWidth, termHeight int) (x, y int) {
+	return max((termWidth-m.w)/2, 0), max((termHeight-m.h)/2, 0)
+}
+
+// listTop is the line of the popup (border, title, search, rule) where the
+// list starts.
+const listTop = 4
+
+// Click handles a left click at cell (x, y) of a terminal of the given size.
+// inside reports whether the click was within the popup. If it hit a branch,
+// that branch is selected and hit is true.
+func (m *Model) Click(x, y, termWidth, termHeight int) (inside, hit bool) {
+	ox, oy := m.Origin(termWidth, termHeight)
+	x, y = x-ox, y-oy
+	if x < 0 || y < 0 || x >= m.w || y >= m.h {
+		return false, false
+	}
+	row := y - listTop
+	if m.loading || m.err != nil || x == 0 || x == m.w-1 || row < 0 || row >= m.rows || m.offset+row >= len(m.shown) {
+		return true, false
+	}
+	m.cursor = m.offset + row
+	return true, true
 }
 
 // row renders one branch: the name, right-aligned the short SHA and age.

internal/tui/branches/branches_test.go

@@ -127,3 +127,44 @@ func TestListScrollsInASmallTerminal(t *testing.T) {
 		t.Errorf("cursor %d outside the window [%d,%d)", m.cursor, m.offset, m.offset+m.rows)
 	}
 }
+
+func TestClickSelectsTheBranchUnderTheMouse(t *testing.T) {
+	m := New(theme.Default(), "src/app")
+	m.SetBranches(list())
+	m.View(100, 30)
+	x, y := m.Origin(100, 30)
+
+	if inside, hit := m.Click(x+3, y+listTop+1, 100, 30); !inside || !hit || name(m) != "dev" {
+		t.Errorf("click on the 2nd row: inside=%v hit=%v selected %q", inside, hit, name(m))
+	}
+	if inside, hit := m.Click(x+3, y+listTop+3, 100, 30); !inside || !hit || name(m) != "origin/feat/search" {
+		t.Errorf("click on the 4th row: inside=%v hit=%v selected %q", inside, hit, name(m))
+	}
+	for _, c := range []struct {
+		name string
+		x, y int
+	}{
+		{"title", x + 3, y + 1},
+		{"search line", x + 3, y + 2},
+		{"hint line", x + 3, y + m.h - 2},
+		{"left border", x, y + listTop},
+	} {
+		before := name(m)
+		if inside, hit := m.Click(c.x, c.y, 100, 30); !inside || hit || name(m) != before {
+			t.Errorf("click on the %s: inside=%v hit=%v selected %q", c.name, inside, hit, name(m))
+		}
+	}
+	if inside, hit := m.Click(0, 0, 100, 30); inside || hit {
+		t.Errorf("click outside: inside=%v hit=%v", inside, hit)
+	}
+}
+
+func TestClickBelowTheLastBranchHitsNothing(t *testing.T) {
+	m := New(theme.Default(), "x")
+	m.SetBranches(list()[:1]) // 1 branch, the list is padded to 3 rows
+	m.View(100, 30)
+	x, y := m.Origin(100, 30)
+	if inside, hit := m.Click(x+3, y+listTop+2, 100, 30); !inside || hit {
+		t.Errorf("inside=%v hit=%v on an empty row", inside, hit)
+	}
+}

internal/tui/overlay.go

@@ -7,28 +7,27 @@ import (
 	"github.com/charmbracelet/x/ansi"
 )
 
-// overlay draws fg centered over bg, which is w x h cells. bg must be the
+// overlay draws fg over bg with its top-left cell at (x, y). bg must be the
 // final string (after zone.Scan): its lines are cut at the popup's edges.
 // The backdrop loses its colors and is drawn in dim, so the popup stands out.
-func overlay(bg, fg string, w, h int, dim lipgloss.Style) string {
+func overlay(bg, fg string, x, y int, dim lipgloss.Style) string {
 	lines := strings.Split(bg, "\n")
 	for i, l := range lines {
 		lines[i] = dim.Render(ansi.Strip(l))
 	}
 	pop := strings.Split(fg, "\n")
 	pw := lipgloss.Width(fg)
-	top := max((h-len(pop))/2, 0)
-	left := max((w-pw)/2, 0)
+	left := x
 	for i, p := range pop {
-		y := top + i
-		if y >= len(lines) {
+		row := y + i
+		if row >= len(lines) {
 			break
 		}
-		line := lines[y]
+		line := lines[row]
 		if lw := ansi.StringWidth(line); lw < left {
 			line += strings.Repeat(" ", left-lw)
 		}
-		lines[y] = ansi.Truncate(line, left, "") + "\x1b[0m" + p + "\x1b[0m" + ansi.TruncateLeft(line, left+pw, "")
+		lines[row] = ansi.Truncate(line, left, "") + "\x1b[0m" + p + "\x1b[0m" + ansi.TruncateLeft(line, left+pw, "")
 	}
 	return strings.Join(lines, "\n")
 }

internal/tui/overlay_test.go

@@ -11,7 +11,7 @@ import (
 
 func TestOverlayCentersThePopup(t *testing.T) {
 	bg := strings.Repeat(strings.Repeat(".", 10)+"\n", 4) + strings.Repeat(".", 10)
-	got := strings.Split(ansi.Strip(overlay(bg, "ab\ncd", 10, 5, lipgloss.NewStyle())), "\n")
+	got := strings.Split(ansi.Strip(overlay(bg, "ab\ncd", 4, 1, lipgloss.NewStyle())), "\n")
 	want := []string{"..........", "....ab....", "....cd....", "..........", ".........."}
 	if len(got) != len(want) {
 		t.Fatalf("got %d lines", len(got))
@@ -26,7 +26,7 @@ func TestOverlayCentersThePopup(t *testing.T) {
 func TestOverlayDimsTheBackdrop(t *testing.T) {
 	bg := "\x1b[31mredredred\x1b[0m"
 	dim := lipgloss.NewStyle().Foreground(lipgloss.Color("8"))
-	got := overlay(bg, "X", 9, 1, dim)
+	got := overlay(bg, "X", 4, 0, dim)
 	if ansi.StringWidth(got) != 9 || ansi.Strip(got) != "redrXdred" {
 		t.Errorf("got %q", ansi.Strip(got))
 	}

internal/tui/switch.go

@@ -77,19 +77,49 @@ func (m Model) pickBranch(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 	case tea.KeyPgDown:
 		m.picker.PageDown()
 	case tea.KeyEnter:
-		b := m.picker.Selected()
-		if b == nil {
-			return m, nil
-		}
-		s := m.byPath[m.pickerPath]
-		m.picker = nil
-		if s == nil || m.restore != nil {
-			return m, nil
-		}
-		m.restore = &restoreState{path: s.Path, name: restoreName(s), branch: b}
-		return m.checkRestore()
+		return m.confirmPick()
 	default:
 		return m, m.picker.Update(msg)
 	}
 	return m, nil
 }
+
+// confirmPick closes the picker and switches to the selected branch, with
+// the same check and question as a restore.
+func (m Model) confirmPick() (tea.Model, tea.Cmd) {
+	b := m.picker.Selected()
+	if b == nil {
+		return m, nil
+	}
+	s := m.byPath[m.pickerPath]
+	m.picker = nil
+	if s == nil || m.restore != nil {
+		return m, nil
+	}
+	m.restore = &restoreState{path: s.Path, name: restoreName(s), branch: b}
+	return m.checkRestore()
+}
+
+// mousePicker handles the mouse while the picker is open: the wheel moves
+// the selection, a click on a branch switches to it, a click outside the
+// popup closes it.
+func (m Model) mousePicker(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
+	switch msg.Button {
+	case tea.MouseButtonWheelUp:
+		m.picker.Up()
+	case tea.MouseButtonWheelDown:
+		m.picker.Down()
+	case tea.MouseButtonLeft:
+		if msg.Action != tea.MouseActionPress {
+			return m, nil
+		}
+		inside, hit := m.picker.Click(msg.X, msg.Y, m.width, m.height)
+		switch {
+		case hit:
+			return m.confirmPick()
+		case !inside:
+			m.picker = nil
+		}
+	}
+	return m, nil
+}

internal/tui/switch_test.go

@@ -180,3 +180,45 @@ func TestSwitchReportsADetachedHead(t *testing.T) {
 		t.Errorf("flash lacks the detached note:\n%s", v)
 	}
 }
+
+// clickRow clicks the i-th visible branch of the open picker.
+func clickRow(m tea.Model, i int) (tea.Model, tea.Cmd) {
+	mm := m.(Model)
+	x, y := mm.picker.Origin(mm.width, mm.height)
+	return m.Update(tea.MouseMsg{X: x + 3, Y: y + 4 + i, Button: tea.MouseButtonLeft, Action: tea.MouseActionPress})
+}
+
+func TestSwitchClickOnABranchSwitches(t *testing.T) {
+	m, f := newSwitchModel(t, submodule.Loss{})
+	m = openPicker(t, m)
+	m.View() // the popup learns where it is drawn
+	m, cmd := clickRow(m, 1)
+	if m.(Model).picker != nil {
+		t.Error("the click must close the picker")
+	}
+	settle(m, cmd)
+	if len(f.switched) != 1 || f.switched[0] != " refs/remotes/origin/feat" {
+		t.Fatalf("switched %q, want the clicked branch", f.switched)
+	}
+}
+
+func TestSwitchClickOutsideClosesAndWheelMoves(t *testing.T) {
+	m, f := newSwitchModel(t, submodule.Loss{})
+	m = openPicker(t, m)
+	m.View()
+	m, _ = m.Update(tea.MouseMsg{Button: tea.MouseButtonWheelDown, Action: tea.MouseActionPress})
+	if b := m.(Model).picker.Selected(); b == nil || b.Name != "origin/feat" {
+		t.Errorf("wheel down selected %v", b)
+	}
+	// a click that releases or sits inside the popup's frame does nothing
+	mm := m.(Model)
+	x, y := mm.picker.Origin(mm.width, mm.height)
+	m, _ = m.Update(tea.MouseMsg{X: x + 3, Y: y + 1, Button: tea.MouseButtonLeft, Action: tea.MouseActionPress})
+	if m.(Model).picker == nil {
+		t.Fatal("a click on the title must keep the popup open")
+	}
+	m, _ = m.Update(tea.MouseMsg{X: 0, Y: 0, Button: tea.MouseButtonLeft, Action: tea.MouseActionPress})
+	if m.(Model).picker != nil || len(f.switched) != 0 {
+		t.Fatal("a click outside must close without switching")
+	}
+}