Rust panics when terminal is too small

[k2d222]

When the terminal gets too small to fit some widget, helix crashes.

Reproduction steps

• Open helix in a resizable terminal.
• Open the file picker (<space> f)
• Resize the window to about 4 rows or 4 cols
• => crash

Stumbled upon this bug when using hx in a drop-down terminal, which apparently resizes the window when hidden.

Environment

• Platform: Linux (tested on gnome-terminal)
• Helix version: current master branch

[kirawi]

😅
\cc @archseer Maybe we should have a test to check for crashes with any of the UI elements on small terminal sizes?

helix/helix-term/src/ui/picker.rs

Lines 507 to 508 in bcf3808

	let rows = inner.height;
	let offset = self.cursor / (rows as usize) * (rows as usize);

Should be as simple as std::cmp::max(1, (row as usize) * (rows as usize))

[archseer]

I think we need to just ignore out of bound render offsets.

(I personally can't even shrink my window that small so I can't reproduce. Can you at least include a backtrace?)

[kirawi]

Found another panic.

thread 'main' panicked at 'index out of bounds: the len is 115 but the index is 161', C:\Users\there\Desktop\helix\
helix-tui\src\buffer.rs:298:17
stack backtrace:
   0: std::panicking::begin_panic_handler at /rustc/8f117a77d0880ed59afcc1a19c72ec5c1e44b97c\/library\std\src\panicking.rs:498

Edit: Nevermind, looks like a propagated panic from the same source issue,

[archseer]

Should be as simple as std::cmp::max(1, (row as usize) * (rows as usize))

Yeah that looks right.

[kirawi]

(The original panic was a divide by 0 panic on line 508)

[k2d222]

The div by 0 is not the only issue: The get and get_mut methods for Buffer panic when out of bounds.

I think it would be safer and more idiomatic to return Option and implement Index and IndexMut to panic. It would mirror the way Vec works. So whenever you're sure there is no overflow, use subscript operator [] (which has a well-known panic semantic) otherwise perform bound checks with the Option.

helix/helix-tui/src/buffer.rs

Line 165 in a066f59

pub fn get(&self, x: u16, y: u16) -> &Cell {

Another solution would be to always perform the bounds checks and to return a dummy Cell when out of bounds. I dislike this one.