Grid::insert_{row, col}() can create invalid states after panicking

[LegionMammal978]

The Grid type has the effective safety invariants that rows.checked_mul(cols) == Some(data.len()) and that rows == 0 if and only if cols == 0. In some panicking paths, Grid::insert_row() can violate these invariants:

• grid.insert_row(i, row) in release mode, where row.len() == grid.cols and grid.rows == usize::MAX. This sets grid.rows to 0, making the other methods' results inconsistent with one another. This is only possible when size_of::<T>() == 0, and I'm not sure if it can cause any UB by itself.
• grid.insert_row(i, row), where i <= grid.rows, row.len() == grid.cols, grid.rows < usize::MAX, and grid.rows * grid.cols > usize::MAX - grid.cols: This increments grid.rows without pushing the new row, allowing invalid get_unchecked() calls. Since this is only possible when size_of::<T>() == 0, it causes library UB but not language UB with the current standard library.
• grid.insert_row(i, row), where i <= grid.rows, row.len() == grid.cols, size_of::<T>() > 0, and (grid.rows + 1) * grid.cols * size_of::<T>() > isize::MAX as usize. This increments grid.rows without pushing the new row, which can cause UB on 32-bit targets:

  /*
  [dependencies]
  grid = "=0.8.1"
  
  cargo run --target i686-unknown-linux-gnu
  */
  
  use grid::Grid;
  use std::panic::{self, AssertUnwindSafe};
  
  fn main() {
      let catch = |f| panic::catch_unwind(AssertUnwindSafe(f)).unwrap_err();
      // 1076 * 1994889 == isize::MAX as usize - 983083
      // 1077 * 1994889 == isize::MAX as usize + 1011806
      let mut grid = Grid::init(1076, 1994889, 0u8);
      catch(|| grid.insert_row(1076, vec![0; 1994889]));
      println!("{}", grid.get(1076, 1994888).unwrap()); // segfault
  }

[becheran]

Interesting. Thanks! I guess the solution to this is to panic earlier so the UB is not possible.

[LegionMammal978]

Also, it appears that insert_row() cannot be used to add a row to an empty grid, which might be useful to support. And a similar issue occurs with insert_col(): the insert() loop can panic partway through, leaving data.len() as a non-multiple of rows. It would probably be best to reserve() the needed capacity before modifying anything.

[becheran]

Fixed with by updating index after altering vector and also added possibility to insert into empty grids