## Summary
Fixes RefCell borrow panic on Linux (Wayland and X11) when callbacks try
to register new callbacks.
**Root cause:** Linux GPUI backends invoked callbacks while still
holding a `RefCell` borrow on the `Callbacks` struct. If a callback
tried to register a new
callback (e.g., `on_window_should_close`), it would panic with "already
borrowed: BorrowMutError".
**Bug pattern:**
```rust
// Callback runs while borrow is held - panics if callback borrows
callbacks
if let Some(ref mut fun) = self.callbacks.borrow_mut().input {
fun(input);
}
Fix: Apply the take-call-restore pattern (already used in macOS
backend):
// Take callback out, release borrow, call, restore
let callback = self.callbacks.borrow_mut().input.take();
if let Some(mut fun) = callback {
let result = fun(input);
self.callbacks.borrow_mut().input = Some(fun);
}
Changes
- Wayland (window.rs): Fixed 6 callback invocations
- X11 (window.rs): Fixed 4 callback invocations
Test plan
- cargo check -p gpui compiles successfully
- Tested on Linux (Wayland) - no more RefCell panic
Release Notes:
- Fixed a crash on Linux when window callbacks attempted to register new
callbacks
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
