Fix fallbacking when creating context fails.

[sarna]

Hi!

I'm getting the same error with every example I try to run. The shortest code that triggers it, after deleting a bunch of lines from the window example:

mod support;

use glutin::event::{Event, WindowEvent};
use glutin::event_loop::{ControlFlow, EventLoop};
use glutin::window::WindowBuilder;
use glutin::ContextBuilder;
use glutin::GlRequest;
use glutin::GlProfile;
use glutin::Api;

fn main() {
    let el = EventLoop::new();
    let wb = WindowBuilder::new().with_title("A fantastic window!");

    let windowed_context =
        ContextBuilder::new().with_gl(GlRequest::Specific(Api::OpenGl, (3, 2))).build_windowed(wb, &el).unwrap();
}

The error itself:

sarna@ub:~/git/glutin$ RUST_BACKTRACE=1 cargo run --example window
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/examples/window`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: CreationErrors([OpenGlVersionNotSupported, OpenGlVersionNotSupported])', src/libcore/result.rs:999:5
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   4: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:474
   5: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:381
   6: rust_begin_unwind
             at src/libstd/panicking.rs:308
   7: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
   8: core::result::unwrap_failed
             at /rustc/8dd4aae9a83964cc08505da92d07ec68a3a2341d/src/libcore/macros.rs:18
   9: core::result::Result<T,E>::unwrap
             at /rustc/8dd4aae9a83964cc08505da92d07ec68a3a2341d/src/libcore/result.rs:800
  10: window::main
             at glutin_examples/examples/window.rs:16
  11: std::rt::lang_start::{{closure}}
             at /rustc/8dd4aae9a83964cc08505da92d07ec68a3a2341d/src/libstd/rt.rs:64
  12: std::panicking::try::do_call
             at src/libstd/rt.rs:49
             at src/libstd/panicking.rs:293
  13: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:85
  14: std::rt::lang_start_internal
             at src/libstd/panicking.rs:272
             at src/libstd/panic.rs:388
             at src/libstd/rt.rs:48
  15: std::rt::lang_start
             at /rustc/8dd4aae9a83964cc08505da92d07ec68a3a2341d/src/libstd/rt.rs:64
  16: main
  17: __libc_start_main
  18: _start

Changing the profile doesn't work. Same thing happens when I request (3,2). And I'm requesting a specific API, because if I don't, I end up with (Api::OpenGlEs, None) for some reason.

My specs and more info here: ggez/ggez#626

[goddessfreya]

Can you run a git bisect to identify the first commit to break the window example?

[felixrabe]

Some specs from the referenced issue (ggez/ggez#626):

My setup:
GPU: Nvidia GeForce GT 240
Drivers: version 340.107 from nvidia-349 (proprietary, tested)
OS: Ubuntu LTS 18.04
WM: Gnome

[goddessfreya]

Yes, I saw. Can you run a git bisect to identify the first commit to break the window example?

https://git-scm.com/docs/git-bisect

Post the results here: https://github.com/rust-windowing/glutin#contact-us

[goddessfreya]

After hours of us debugging, this was tracked down to two things:

This line, which I accidentally left in and was planning to remove in my next commit:
https://github.com/rust-windowing/glutin/blob/master/glutin/src/platform_impl/unix/x11.rs#L323

And the NVIDIA proprietary driver's lack of support for EGL.

The solution is simple, either remove the line mentioned above (recommended) or switch to Nouveau.

[goddessfreya]

Nevertheless, the EGL fall backing code is pretty sad. In fact, I think all the impls of Latest are broken, so, yeah. Something to fix for the next release.

[goddessfreya]

Should be noted, the original bug got fixed here: 0926279

[goddessfreya]

In v0.24, you must now specify the exact version you want. Version fallbacking code is left for clients to implement. See #1271 for details on the API changes. Closing.