"No backend is available" error with examples

[vanzef]

I am trying to build and run an example from piston.rs, here is the code fore reference:

extern crate piston_window;

use piston_window::*;

fn main() {
    let mut window: PistonWindow = 
        WindowSettings::new("Hello Piston!", [640, 480])
        .exit_on_esc(true).build().unwrap();
    while let Some(e) = window.next() {
        window.draw_2d(&e, |c, g| {
            clear([1.0; 4], g);
            rectangle([1.0, 0.0, 0.0, 1.0], // red
                      [0.0, 0.0, 100.0, 100.0],
                      c.transform, g);
        });
    }
}

but get error:

     Running `target/debug/example`
thread 'main' panicked at 'No backend is available', /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/winit-0.12.0/src/platform/linux/mod.rs:356:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:475
   5: std::panicking::begin_panic
             at /checkout/src/libstd/panicking.rs:409
   6: winit::platform::platform::EventsLoop::new
             at /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/winit-0.12.0/src/platform/linux/mod.rs:356
   7: winit::EventsLoop::new
             at /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/winit-0.12.0/src/lib.rs:195
   8: glutin_window::GlutinWindow::new
             at /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/pistoncore-glutin_window-0.47.0/src/lib.rs:102
   9: <glutin_window::GlutinWindow as window::BuildFromWindowSettings>::build_from_window_settings
             at /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/pistoncore-glutin_window-0.47.0/src/lib.rs:449
  10: window::WindowSettings::build
             at /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/pistoncore-window-0.32.0/src/lib.rs:392
  11: <piston_window::PistonWindow<W> as window::BuildFromWindowSettings>::build_from_window_settings
             at /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/piston_window-0.80.0/src/lib.rs:152
  12: window::WindowSettings::build
             at /home/user/.local/share/cargo/registry/src/github.ghproxy.top-1ecc6299db9ec823/pistoncore-window-0.32.0/src/lib.rs:392
  13: example::main
             at src/main.rs:96
  14: std::rt::lang_start::{{closure}}
             at /checkout/src/libstd/rt.rs:74
  15: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  16: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:106
  17: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  18: std::rt::lang_start
             at /checkout/src/libstd/rt.rs:74
  19: main
  20: __libc_start_main
  21: _start
             at ../sysdeps/x86_64/start.S:120

I am running NixOS, so problem may be with dynamically loading libraries. Is there a way to find out which
libs do I need?

As far as I can understand the problem is in XConnection::new function:

    pub fn new(error_handler: XErrorHandler) -> Result<XConnection, XNotSupported> {
        // opening the libraries
        let xlib = try!(ffi::Xlib::open());
        let xcursor = try!(ffi::Xcursor::open());
        let xrandr = try!(ffi::Xrandr_2_2_0::open());
        let xrandr_1_5 = ffi::Xrandr::open().ok();
        let xinput2 = try!(ffi::XInput2::open());
        let xlib_xcb = try!(ffi::Xlib_xcb::open());

        unsafe { (xlib.XInitThreads)() };
        unsafe { (xlib.XSetErrorHandler)(error_handler) };

        // calling XOpenDisplay
        let display = unsafe {
            let display = (xlib.XOpenDisplay)(ptr::null());
            if display.is_null() {
                return Err(XNotSupported::XOpenDisplayFailed);
            }
            display
        };

        Ok(XConnection {
            xlib: xlib,
            xrandr: xrandr,
            xrandr_1_5: xrandr_1_5,
            xcursor: xcursor,
            xinput2: xinput2,
            xlib_xcb: xlib_xcb,
            display: display,
            latest_error: Mutex::new(None),
        })
    }

I've tried to explicitly "install" all mentioned libs via nix-shell -p "[x11 gcc] ++ (with xorg; [libXcursor xrandr xinput libxcb])", but got the same error as above.

[nrdxp]

The source of the issue is glutin. More details available in this closed issue.

I fixed the issue myself by building a simple nix package in the root of the cargo directory:

let
  nixpkgs = import <nixpkgs> {};
  inherit (nixpkgs) mesa libGL patchelf rustPlatform wayland xorg;
  inherit (xorg) libX11 libXcursor libXi libXxf86vm;
in
rustPlatform.buildRustPackage rec {
  pname = "spinning-square";
  version = "0.1.0";

  src = ./.;

  cargoSha256 = "...";

  buildInputs = [ patchelf ];

  fixupPhase = ''
    patchelf --set-rpath ${libGL}/lib:${mesa}/lib:${wayland}/lib:${libX11}/lib:${libXi}/lib:${libXcursor}/lib:${libXxf86vm}/lib \
    $out/bin/spinning-square
  '';
}

The most important part here is the patchelf call where we modify the ELF binaries rpath to contain valid directions to all the listed directories. This should allow it run in both wayland and xorg on NixOS.

This can probably be marked as solved now. If the maintainer wishes to document this somewhere please do. Maybe even just a link to this issue in the readme so people on NixOS don't get stuck and quit trying.

[garaiza-93]

Found this issue after going through the same struggle with backend errors, and I am also on NixOS. For others that find this, the package above is a good solution!
However. somewhere between now and then. glutin now requires libXrandr, but that's just easily extending the patchelf command to include it.

Here's my entire flake if anyone wants it.

{
  description = "Basic Rust environment with toolchain and language server";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { nixpkgs, flake-utils, ... }:
    flake-utils.lib.eachDefaultSystem
      (system:
        let
          pkgs = nixpkgs.legacyPackages.${system};
          inherit (pkgs) mkShell rust mesa libGL patchelf rustPlatform wayland xorg;
          inherit (xorg) libX11 libXcursor libXi libXxf86vm libXrandr;

          pname = "simple-game";
          version = "0.1.0";

          nvimrc = ''local servers = { "rust_analyzer" }
            local caps = require("cmp_nvim_lsp").default_capabilities(vim.lsp.protocol.make_client_capabilities());
            for _, lsp in ipairs(servers) do
              require("lspconfig")[lsp].setup {capabilities = caps}
            end

            vim.cmd("LspStart");'';
        in
        rec
        {
          # Executed by `nix build`
          packages.default = rustPlatform.buildRustPackage {
            inherit pname version;
            src = ./.;
            cargoLock.lockFile = ./Cargo.lock;

            buildInputs = [ patchelf ];

            fixupPhase = ''
              patchelf --set-rpath ${libGL}/lib:${mesa}/lib:${wayland}/lib:${libX11}/lib:${libXi}/lib:${libXcursor}/lib:${libXxf86vm}/lib:${libXrandr}/lib \
              $out/bin/${pname}
            '';
          };

          # Executed by `nix run`
          apps.default = flake-utils.lib.mkApp { drv = packages.default; };

          # Used by `nix develop`
          devShells.default = mkShell {

            buildInputs = with pkgs; [
              cargo
              rustc
              clippy
              rustfmt
              rust-analyzer
              pkg-config
            ];

            RUST_SRC_PATH = "${rust.packages.stable.rustPlatform.rustLibSrc}";

            shellHook = ''echo '${nvimrc}' > .nvimrc.lua'';
          };
        }
      );
}