Fix SIGWINCH handler type casting in switch_modes function add instructions for copilot

.github/copilot-instructions.md

@@ -0,0 +1,54 @@
+## Purpose
+Short, actionable notes to help AI coding agents be productive in this repository (microsoft/edit).
+
+## Big picture (what to change and where)
+- Single crate Rust editor. Core library code lives in `src/` and the CLI/UI binary is `src/bin/edit/`.
+- UI loop and terminal handling are centered in `src/bin/edit/main.rs` (vt parser, input parser, TUI render loop).
+- Platform abstractions and low-level IO live in `src/sys/` (`unix.rs`, `windows.rs`). Prefer changes here for platform behavior.
+- Memory allocation / temporary buffers use the project's arena allocator in `src/arena/` (look for `Arena`, `ArenaString`, `scratch_arena`).
+- Internationalization is generated at build time from `i18n/edit.toml` by the build script `build/main.rs` and included via `include!(concat!(env!("OUT_DIR"), "/i18n_edit.rs"));` in `src/bin/edit/localization.rs`.
+
+## Important developer workflows & commands
+- Recommended toolchain: Rust stable per `rust-toolchain.toml` but README suggests nightly for some builds. If you can't use nightly, `RUSTC_BOOTSTRAP=1` is an alternative.
+- Debug (local):
+  - cargo build (normal)
+  - cargo run -p edit -- <args> (run the editor binary)
+  - To enable latency instrumentation: `cargo build --package edit --features debug-latency` (this is used in the TUI loop).
+- Release: follow README — either
+  - `cargo build --config .cargo/release.toml --release` (older rust) or
+  - `cargo build --config .cargo/release-nightly.toml --release` (when README instructs nightly-specific config).
+- Tests and ignored tests: `cargo test`. Some tests are intentionally marked ignored and require environment tweaks — run `cargo test -- --ignored` to exercise them.
+- Benchmarks: `cargo bench` (project uses `criterion`).
+
+## Build-time environment and integration points
+- i18n: `build/main.rs` reads `i18n/edit.toml` and writes `OUT_DIR/i18n_edit.rs`. Rebuild on changes to `i18n/edit.toml`.
+- ICU (optional): the build script emits env vars consumed by code. Important envs:
+  - `EDIT_CFG_ICUUC_SONAME`, `EDIT_CFG_ICUI18N_SONAME`, `EDIT_CFG_ICU_CPP_EXPORTS`, `EDIT_CFG_ICU_RENAMING_VERSION`, `EDIT_CFG_ICU_RENAMING_AUTO_DETECT`.
+  - These affect `src/sys/*.rs` and `src/icu.rs` where dynamic symbol names are composed using `env!("EDIT_CFG_...")`.
+  - Example (Linux): `EDIT_CFG_ICUUC_SONAME=libicuuc.so EDIT_CFG_ICUI18N_SONAME=libicui18n.so cargo build`.
+
+## Project-specific patterns and conventions
+- Arena-first memory: many data structures use `Arena` and `ArenaString` for short-lived allocations. Prefer these for UI paths and avoid heap-allocating large temporaries.
+- `scratch_arena(None)` is commonly used to create ephemeral buffers inside hot loops — be careful when refactoring to not extend lifetimes.
+- UI code is modularized as `draw_*` modules under `src/bin/edit/` (e.g., `draw_editor.rs`, `draw_menubar.rs`) — add UI elements by following the existing `draw_*` patterns.
+- Buffer logic is in `buffer/` (gap buffer, line cache, navigation). Changes that affect on-disk or undo behavior likely live there.
+- Platform-specific code in `src/sys` is authoritative for terminal and file IO. Changes to terminal modes, raw input, or clipboard should be made there.
+- Use existing macro helpers: `arena_format!`, `KIBI`, `MEBI`, and `MetricFormatter` when producing formatted strings to match style and memory usage.
+
+## Where to look for common tasks (quick map)
+- Add a UI control/widget: `src/bin/edit/draw_*.rs` + `src/bin/edit/state.rs`.
+- Change buffer semantics: `buffer/gap_buffer.rs`, `buffer/line_cache.rs`, `buffer/navigation.rs`.
+- Localization strings: `i18n/edit.toml` -> `build/main.rs` generates `OUT_DIR/i18n_edit.rs` -> included in `src/bin/edit/localization.rs`.
+- Terminal/TTY behavior: `src/sys/unix.rs` and `src/sys/windows.rs` and `src/bin/edit/main.rs` (setup_terminal, RestoreModes).
+- Low-level unicode/width handling: `src/unicode/*` and `src/icu.rs`.
+
+## Safety and testing notes for agents
+- Avoid modifying unsafe, low-level allocator and lifetime-sensitive code (arena, buffer internals) without running quick checks — these are delicate and rely on invariants across many modules.
+- Many behaviors are environment-dependent (terminals, ICU libs). When adding tests, prefer unit tests in `src/` that don't rely on terminal IO; integration tests that require terminal emulation are flakier.
+
+## Example quick tasks and references
+- Run editor on a file: `cargo run -p edit -- README.md` — useful to manually validate UI changes.
+- Find localization usage: `src/bin/edit/localization.rs` (includes generated file) and `i18n/edit.toml` (source).
+- See platform wrappers: `src/sys/mod.rs`, `src/sys/unix.rs`, `src/sys/windows.rs`.
+
+If anything here is unclear or you'd like additional examples (e.g., small code-change + test cycle for a UI change), tell me which area to expand and I will iterate.

src/sys/unix.rs

@@ -76,7 +76,7 @@ pub fn switch_modes() -> apperr::Result<()> {
 
         // Set STATE.inject_resize to true whenever we get a SIGWINCH.
         let mut sigwinch_action: libc::sigaction = mem::zeroed();
-        sigwinch_action.sa_sigaction = sigwinch_handler as libc::sighandler_t;
+        sigwinch_action.sa_sigaction = sigwinch_handler as *const c_void as libc::sighandler_t;
         check_int_return(libc::sigaction(libc::SIGWINCH, &sigwinch_action, null_mut()))?;
 
         // Get the original terminal modes so we can disable raw mode on exit.