tentatively fixes gyscos#776

cursive-core/src/views/menu_popup.rs

@@ -130,7 +130,11 @@ impl MenuPopup {
  } else if cycle {
  // Only cycle once to prevent endless loop
  cycle = false;
- self.focus = self.menu.children.len() - 1;
+ let len = self.menu.children.len();
+ if len == 0 {
+ break;
+ }
+ self.focus = len - 1;
  } else {
  break;
  }
@@ -143,12 +147,16 @@ impl MenuPopup {
 
  fn scroll_down(&mut self, mut n: usize, mut cycle: bool) {
  while n > 0 {
- if self.focus + 1 < self.menu.children.len() {
+ let len = self.menu.children.len();
+ if self.focus + 1 < len {
  self.focus += 1;
  } else if cycle {
  // Only cycle once to prevent endless loop
  cycle = false;
  self.focus = 0;
+ if len == 0 {
+ break;
+ }
  } else {
  // Stop if we're at the bottom.
  break;
@@ -236,13 +244,19 @@ impl MenuPopup {
  Event::Key(Key::Home) => self.focus = 0,
  Event::Key(Key::End) => self.focus = self.menu.children.len().saturating_sub(1),
 
- Event::Key(Key::Right) if self.menu.children[self.focus].is_subtree() => {
+ Event::Key(Key::Right)
+ if (self.focus < self.menu.children.len()
+ && self.menu.children[self.focus].is_subtree()) =>
+ {
  return match self.menu.children[self.focus] {
  menu::Item::Subtree { ref tree, .. } => self.make_subtree_cb(tree),
  _ => unreachable!("Child is a subtree"),
  };
  }
- Event::Key(Key::Enter) if self.menu.children[self.focus].is_enabled() => {
+ Event::Key(Key::Enter)
+ if (self.focus < self.menu.children.len()
+ && self.menu.children[self.focus].is_enabled()) =>
+ {
  return self.submit();
  }
  Event::Mouse {
@@ -263,7 +277,8 @@ impl MenuPopup {
  event: MouseEvent::Release(MouseButton::Left),
  position,
  offset,
- } if self.menu.children[self.focus].is_enabled()
+ } if (self.focus < self.menu.children.len()
+ && self.menu.children[self.focus].is_enabled())
  && position
  .checked_sub(offset)
  .map(|position| position.y == self.focus)
@@ -320,7 +335,13 @@ impl View for MenuPopup {
  scroll::draw_box_frame(
  self,
  printer,
- |s, y| s.menu.children[y].is_delimiter(),
+ |s, y| {
+ if s.menu.children.len() > y {
+ s.menu.children[y].is_delimiter()
+ } else {
+ false
+ }
+ },
  |_s, _x| false,
  );