cinny-desktop/src-tauri/src/gpu_workarounds.rs

//! WebKitGTK workarounds for NVIDIA's proprietary driver on Linux.
//!
//! On NVIDIA + Wayland (reported on CachyOS/KDE, driver 615, webkit2gtk 2.52)
//! the app never shows a window: GDK dies with "Error 71 (Protocol error)
//! dispatching to Wayland display", and under XWayland WebKit's DMA-BUF
//! renderer then fails with "Failed to create GBM buffer … Invalid argument".
//! `WEBKIT_DISABLE_DMABUF_RENDERER=1 GDK_BACKEND=x11` makes it run normally.
//!
//! So, before GTK/WebKit initialise, and only when the NVIDIA driver is loaded:
//! - `WEBKIT_DISABLE_DMABUF_RENDERER=1`;
//! - on a Wayland session with XWayland available, `GDK_BACKEND=x11`.
//!
//! Anything the user already set wins, and `LOTUS_NO_GPU_WORKAROUNDS=1`
//! disables all of it (e.g. once a newer driver/WebKit fixes this).

/// Environment variables to set: pure, for tests.
pub(crate) fn decide(
    nvidia: bool,
    get: impl Fn(&str) -> Option<String>,
) -> Vec<(&'static str, &'static str)> {
    let set = |k: &str| get(k).is_some_and(|v| !v.is_empty());
    if !nvidia || set("LOTUS_NO_GPU_WORKAROUNDS") {
        return Vec::new();
    }
    let mut out = Vec::new();
    if !set("WEBKIT_DISABLE_DMABUF_RENDERER") {
        out.push(("WEBKIT_DISABLE_DMABUF_RENDERER", "1"));
    }
    let wayland = set("WAYLAND_DISPLAY")
        || get("XDG_SESSION_TYPE").is_some_and(|v| v.eq_ignore_ascii_case("wayland"));
    // Only fall back to X11 when there is an X server (XWayland) to talk to.
    if wayland && set("DISPLAY") && !set("GDK_BACKEND") {
        out.push(("GDK_BACKEND", "x11"));
    }
    out
}

#[cfg(target_os = "linux")]
fn nvidia_driver_loaded() -> bool {
    std::path::Path::new("/proc/driver/nvidia/version").exists()
        || std::path::Path::new("/sys/module/nvidia").exists()
}

/// Call first thing in `main`, before anything starts GTK or spawns threads.
pub fn apply() {
    #[cfg(target_os = "linux")]
    for (key, value) in decide(nvidia_driver_loaded(), |k| std::env::var(k).ok()) {
        eprintln!("gpu-workarounds: NVIDIA driver detected, setting {key}={value} (LOTUS_NO_GPU_WORKAROUNDS=1 to disable)");
        std::env::set_var(key, value);
    }
}

#[cfg(test)]
mod tests {
    use super::decide;
    use std::collections::HashMap;

    fn run(nvidia: bool, env: &[(&str, &str)]) -> Vec<(&'static str, &'static str)> {
        let map: HashMap<String, String> = env
            .iter()
            .map(|(k, v)| (k.to_string(), v.to_string()))
            .collect();
        decide(nvidia, |k| map.get(k).cloned())
    }

    const WAYLAND: &[(&str, &str)] = &[("WAYLAND_DISPLAY", "wayland-0"), ("DISPLAY", ":0")];

    #[test]
    fn nothing_without_nvidia() {
        assert!(run(false, WAYLAND).is_empty());
    }

    #[test]
    fn nvidia_wayland_gets_both() {
        assert_eq!(
            run(true, WAYLAND),
            vec![
                ("WEBKIT_DISABLE_DMABUF_RENDERER", "1"),
                ("GDK_BACKEND", "x11")
            ]
        );
    }

    #[test]
    fn nvidia_x11_session_only_disables_dmabuf() {
        assert_eq!(
            run(true, &[("DISPLAY", ":0")]),
            vec![("WEBKIT_DISABLE_DMABUF_RENDERER", "1")]
        );
    }

    #[test]
    fn wayland_without_xwayland_keeps_wayland() {
        assert_eq!(
            run(true, &[("WAYLAND_DISPLAY", "wayland-0")]),
            vec![("WEBKIT_DISABLE_DMABUF_RENDERER", "1")]
        );
    }

    #[test]
    fn xdg_session_type_counts_as_wayland() {
        assert_eq!(
            run(true, &[("XDG_SESSION_TYPE", "wayland"), ("DISPLAY", ":1")]),
            vec![
                ("WEBKIT_DISABLE_DMABUF_RENDERER", "1"),
                ("GDK_BACKEND", "x11")
            ]
        );
    }

    #[test]
    fn user_settings_win() {
        let env = [
            ("WAYLAND_DISPLAY", "wayland-0"),
            ("DISPLAY", ":0"),
            ("WEBKIT_DISABLE_DMABUF_RENDERER", "0"),
            ("GDK_BACKEND", "wayland"),
        ];
        assert!(run(true, &env).is_empty());
    }

    #[test]
    fn opt_out_disables_everything() {
        let mut env = WAYLAND.to_vec();
        env.push(("LOTUS_NO_GPU_WORKAROUNDS", "1"));
        assert!(run(true, &env).is_empty());
    }
}