Wgpu: Make libx11 optional on Vulkan

[parasyte]

Description

wgpu-core currently hardcodes the x11 feature on the gfx-backend-vulkan crate for Unix platforms. This has the effect that building on a system with Wayland still requires libx11 development libraries to be installed.

https://github.com/gfx-rs/wgpu/blob/4c136418ff20ed52f4c56b6af3ec419d356a9ac4/wgpu-core/Cargo.toml#L58-L59

Repro steps

Build wgpu-core on a Linux system without libx11. E.g. the clux/muslrust Docker image.

$ docker image pull clux/muslrust:latest
$ docker run -it --rm clux/muslrust:latest

root@8d5e3f85d364:/volume# git clone https://github.com/gfx-rs/wgpu.git
root@8d5e3f85d364:/volume# cd wgpu/
root@8d5e3f85d364:/volume/wgpu# cargo build --package wgpu-core
[...snip...]
error: failed to run custom build command for `x11 v2.18.2`

Caused by:
  process didn't exit successfully: `/volume/wgpu/target/debug/build/x11-28c43b6fae26f5d7/build-script-build` (exit code: 101)
--- stderr
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Failure { command: "\"pkg-config\" \"--static\" \"--libs\" \"--cflags\" \"x11\" \"x11 >= 1.4.99.1\"", output: Output { status: ExitStatus(ExitStatus(256)), stdout: "", stderr: "Package x11 was not found in the pkg-config search path.\nPerhaps you should add the directory containing `x11.pc\'\nto the PKG_CONFIG_PATH environment variable\nPackage \'x11\', required by \'world\', not found\nPackage \'x11\', required by \'world\', not found\n" } }', /root/.cargo/registry/src/github.com-1ecc6299db9ec823/x11-2.18.2/build.rs:36:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

warning: build failed, waiting for other jobs to finish...
error: build failed

Expected vs observed behavior

I believe this dependency can be made optional with a feature flag.

Side note: On the v0.5 branch, wgpu-native has a hardcoded dependency on libx11:

https://github.com/gfx-rs/wgpu/blob/eeda6dcdfd0bdb52c97217e61e2bb195e1b03a4f/wgpu-native/src/device.rs#L50-L56

I don't see any similar limitations on master, so this should be trivial? Ah, I found the new home of wgpu-native, and it still has a hard dependency on libx11. The good news is this crate is no longer in the pure-Rust dependency tree, and it can be handled separately.

Extra materials

Originally reported in https://github.com/parasyte/pixels/issues/83

Platform

Linux/Wayland

[grovesNL]

I guess using the x11 types in gfx doesn't really give us much benefit and the x11 dependency is heavyweight. We've also been trying to avoid using features for backends/environments so features wouldn't be ideal here.

Maybe we could drop the x11 dependency from gfx and just use type aliases/raw types for surface creation? e.g. in raw-window-handle the raw types are located at https://github.com/rust-windowing/raw-window-handle/blob/044e464bb4eaca3c215028199223ecc13831d85d/src/unix.rs#L16-L19). raw-window-handle should work well for most users so using raw types wouldn't be very common anyway.

[kvark]

We can safely remove the dependency requirement and leave it up to the user to enable. I.e. the user may have something like this (in addition to depending on wgpu):

[target.'cfg(all(unix, not(target_os = "ios"), not(target_os = "macos")))'.dependencies]
gfx-backend-vulkan = { version = "0.5", features = ["x11"] }