LinearLayout->BoxView->Panel->TextArea can panic

[simmons]

The TextArea::compute_rows() function panics with an "attempt to subtract with overflow" error if required_size() is called with (0,0). This can occur in normal conditions when LinearLayout::required_size()'s budget layout algorithm is invoked on a horizontally oriented layout, which calls the child required_size() with (1,_), and Panel transforms this to (0,0) when trying to accommodate the border.

I've observed this on the latest master (134854e), and the problem appears to go back to 14cfe36. This is on Linux with the default ncurses backend.

Example code:

extern crate cursive;
use cursive::Cursive;
use cursive::view::*;
use cursive::views::*;
fn main() {
    let mut cursive = Cursive::new();
    cursive.add_layer(LinearLayout::horizontal()
        .child(BoxView::new(SizeConstraint::Full,
                            SizeConstraint::Full,
                            Panel::new(TextArea::new().content("one"))))
        .child(BoxView::new(SizeConstraint::Full,
                            SizeConstraint::Full,
                            Panel::new(TextArea::new().content("two")))));
    cursive.run();
}

Panic with backtrace:

thread 'main' panicked at 'attempt to subtract with overflow', /Users/simmons/work/ref/Cursive/src/views/text_area.rs:205
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
   1: std::panicking::default_hook::{{closure}}
   2: std::panicking::default_hook
   3: std::panicking::rust_panic_with_hook
   4: std::panicking::begin_panic
   5: std::panicking::begin_panic_fmt
   6: rust_begin_unwind
   7: core::panicking::panic_fmt
   8: core::panicking::panic
   9: cursive::views::text_area::TextArea::compute_rows
  10: <cursive::views::text_area::TextArea as cursive::view::View>::required_size
  11: <cursive::views::panel::Panel<V> as cursive::view::view_wrapper::ViewWrapper>::wrap_required_size
  12: cursive::view::view_wrapper::<impl cursive::view::View for T>::required_size
  13: <cursive::views::box_view::BoxView<T> as cursive::view::view_wrapper::ViewWrapper>::wrap_required_size
  14: cursive::view::view_wrapper::<impl cursive::view::View for T>::required_size
  15: cursive::views::linear_layout::Child::required_size
  16: <cursive::views::linear_layout::LinearLayout as cursive::view::View>::required_size::{{closure}}
  17: core::ops::impls::<impl core::ops::FnOnce<A> for &'a mut F>::call_once
  18: <core::option::Option<T>>::map
  19: <core::iter::Map<I, F> as core::iter::iterator::Iterator>::next
  20: <collections::vec::Vec<T> as collections::vec::SpecExtend<T, I>>::spec_extend
  21: <collections::vec::Vec<T> as collections::vec::SpecExtend<T, I>>::from_iter
  22: <collections::vec::Vec<T> as core::iter::traits::FromIterator<T>>::from_iter
  23: core::iter::iterator::Iterator::collect
  24: <cursive::views::linear_layout::LinearLayout as cursive::view::View>::required_size
  25: cursive::view::view_wrapper::ViewWrapper::wrap_required_size::{{closure}}
  26: <cursive::views::layer::Layer<T> as cursive::view::view_wrapper::ViewWrapper>::with_view_mut
  27: cursive::view::view_wrapper::ViewWrapper::wrap_required_size
  28: cursive::view::view_wrapper::<impl cursive::view::View for T>::required_size
  29: <cursive::views::shadow_view::ShadowView<T> as cursive::view::view_wrapper::ViewWrapper>::wrap_required_size
  30: cursive::view::view_wrapper::<impl cursive::view::View for T>::required_size
  31: <cursive::views::stack_view::StackView as cursive::view::View>::layout
  32: cursive::Cursive::layout
  33: cursive::Cursive::step
  34: cursive::Cursive::run
  35: panel_issue_example::main
  36: __rust_maybe_catch_panic
  37: std::rt::lang_start
  38: main

Debug output when instrumenting certain required_size() functions with eprintln!() on a 80x24 terminal:

LinearLayout::required_size(self, req=XY { x: 78, y: 22 })
LinearLayout::required_size(): simple case
linear_layout::Child::required_size(self, req=XY { x: 78, y: 22 })
BoxView::wrap_required_size(self, req=XY { x: 78, y: 22 })
Panel::wrap_required_size(self, req=XY { x: 78, y: 22 })
TextArea::required_size(self="one", constraint=XY { x: 76, y: 20 })
linear_layout::Child::required_size(self, req=XY { x: 78, y: 22 })
BoxView::wrap_required_size(self, req=XY { x: 78, y: 22 })
Panel::wrap_required_size(self, req=XY { x: 78, y: 22 })
TextArea::required_size(self="two", constraint=XY { x: 76, y: 20 })
LinearLayout::required_size(): budget case // budget_req=XY { x: 1, y: 22 }
linear_layout::Child::required_size(self, req=XY { x: 1, y: 22 })
BoxView::wrap_required_size(self, req=XY { x: 1, y: 22 })
Panel::wrap_required_size(self, req=XY { x: 1, y: 22 })
TextArea::required_size(self="one", constraint=XY { x: 0, y: 0 })

[gyscos]

Doh, thanks for the report!

There's still a bunch of not-very-safe subtractions... :S
I fixed TextArea for now; I'll have to go through the other views as well some day.

[gyscos]

I did a first run through unchecked subtractions, and fixed most of those to checked_sub/saturating_sub. I also added those two methods to Vec2 to make checks easier. The result should be published as 0.6.3.