[Bug] Null pointer dereference panic in `single-instance-plugin`

[lars-berger]

Note that this only occurs on the latest Rust nightly nightly-x86_64-pc-windows-msvc (1.86.0). If I rollback to nightly-2024-10-01-x86_64-pc-windows-msvc, then it no longer occurs.

packages/desktop dev: thread 'main' panicked at C:\Users\larsb\.cargo\registry\src\index.crates.io-1949cf8c6b5b557f\tauri-plugin-single-instance-2.2.1\src\platform_impl\windows.rs:121:34:
packages/desktop dev: null pointer dereference occured

Reproduction:

1. Clone https://github.com/glzr-io/zebar
2. git checkout 3058a0dd0694fb168b9ee84027bd260ce14fe60a
3. pnpm i && pnpm dev

Occurs on latest (v2.2.1) of single-instance-plugin

[ferreira-tb]

I can consistently reproduce this up to nightly-2025-02-17-x86_64-pc-windows-msvc (rustc 1.87).
Last working nightly version was nightly-2025-01-31-x86_64-pc-windows-msvc (rustc 1.86).

May be related to: rust-lang/rust#134424

[wlwatkins]

Yep after switching to nightly I get this issue

[Islatri]

I also got same issue after upgrading to rustc 1.87.0-nightly (794c12416 2025-02-21) Σ(ＴωＴ)

thread 'main' panicked at C:\Users\Chest\.cargo\registry\src\index.crates.io-1949cf8c6b5b557f\tauri-plugin-single-instance-2.2.1\src\platform_impl\windows.rs:121:34:
null pointer dereference occurred
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread caused non-unwinding panic. aborting.

It means it panicked at &mut *data_ptr; of the code below

unsafe extern "system" fn single_instance_window_proc<R: Runtime>(
    hwnd: HWND,
    msg: u32,
    wparam: WPARAM,
    lparam: LPARAM,
) -> LRESULT {
    let data_ptr = GetWindowLongPtrW(hwnd, GWL_USERDATA)
        as *mut (AppHandle<R>, Box<SingleInstanceCallback<R>>);
    let (app_handle, callback) = &mut *data_ptr;   // Panicked here