Err when a X connection cannot be created instead of panicking

src/api/x11/mod.rs

@@ -2,7 +2,7 @@
 
 pub use self::monitor::{MonitorID, get_available_monitors, get_primary_monitor};
 pub use self::window::{Window, XWindow, PollEventsIterator, WaitEventsIterator, Context, WindowProxy};
-pub use self::xdisplay::XConnection;
+pub use self::xdisplay::{XConnection, XNotSupported};
 
 pub mod ffi;
 

src/api/x11/xdisplay.rs

@@ -1,4 +1,6 @@
 use std::ptr;
+use std::fmt;
+use std::error::Error;
 use std::ffi::CString;
 
 use libc;
@@ -21,10 +23,6 @@ pub struct XConnection {
 unsafe impl Send for XConnection {}
 unsafe impl Sync for XConnection {}
 
-/// Error returned if this system doesn't have XLib or can't create an X connection.
-#[derive(Copy, Clone, Debug)]
-pub struct XNotSupported;
-
 impl XConnection {
     pub fn new() -> Result<XConnection, XNotSupported> {
         // opening the libraries
@@ -104,3 +102,19 @@ impl Drop for XConnection {
         unsafe { (self.xlib.XCloseDisplay)(self.display) };
     }
 }
+
+/// Error returned if this system doesn't have XLib or can't create an X connection.
+#[derive(Copy, Clone, Debug)]
+pub struct XNotSupported;
+
+impl Error for XNotSupported {
+    fn description(&self) -> &str {
+        "The X windowing system could not be initialized"
+    }
+}
+
+impl fmt::Display for XNotSupported {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        formatter.write_str(self.description())
+    }
+}

src/lib.rs

@@ -106,11 +106,12 @@ pub trait GlContext {
 }
 
 /// Error that can happen while creating a window or a headless renderer.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Debug)]
 pub enum CreationError {
     OsError(String),
     /// TODO: remove this error
     NotSupported,
+    NoBackendAvailable(Box<std::error::Error + Send>),
     RobustnessNotSupported,
     OpenGlVersionNotSupported,
     NoAvailablePixelFormat,
@@ -121,6 +122,7 @@ impl CreationError {
         match *self {
             CreationError::OsError(ref text) => &text,
             CreationError::NotSupported => "Some of the requested attributes are not supported",
+            CreationError::NoBackendAvailable(_) => "No backend is available",
             CreationError::RobustnessNotSupported => "You requested robustness, but it is \
                                                       not supported.",
             CreationError::OpenGlVersionNotSupported => "The requested OpenGL version is not \
@@ -141,6 +143,13 @@ impl std::error::Error for CreationError {
     fn description(&self) -> &str {
         self.to_string()
     }
+
+    fn cause(&self) -> Option<&std::error::Error> {
+        match *self {
+            CreationError::NoBackendAvailable(ref err) => Some(&**err),
+            _ => None
+        }
+    }
 }
 
 /// Error that can happen when manipulating an OpenGL context.

src/platform/linux/api_dispatch.rs

@@ -19,10 +19,12 @@ use libc;
 use api::wayland;
 use api::x11;
 use api::x11::XConnection;
+use api::x11::XNotSupported;
 
 enum Backend {
     X(Arc<XConnection>),
-    Wayland
+    Wayland,
+    Error(XNotSupported),
 }
 
 lazy_static!(
@@ -31,7 +33,10 @@ lazy_static!(
         if false && wayland::is_available() {
             Backend::Wayland
         } else {
-            Backend::X(Arc::new(XConnection::new().unwrap()))
+            match XConnection::new() {
+                Ok(x) => Backend::X(Arc::new(x)),
+                Err(e) => Backend::Error(e),
+            }
         }
     };
 );
@@ -65,7 +70,9 @@ pub enum MonitorID {
     #[doc(hidden)]
     X(x11::MonitorID),
     #[doc(hidden)]
-    Wayland(wayland::MonitorID)
+    Wayland(wayland::MonitorID),
+    #[doc(hidden)]
+    None,
 }
 
 pub fn get_available_monitors() -> VecDeque<MonitorID> {
@@ -78,6 +85,7 @@ pub fn get_available_monitors() -> VecDeque<MonitorID> {
                                     .into_iter()
                                     .map(MonitorID::X)
                                     .collect(),
+        Backend::Error(_) => { let mut d = VecDeque::new(); d.push_back(MonitorID::None); d},
     }
 }
 
@@ -85,6 +93,7 @@ pub fn get_primary_monitor() -> MonitorID {
     match *BACKEND {
         Backend::Wayland => MonitorID::Wayland(wayland::get_primary_monitor()),
         Backend::X(ref connec) => MonitorID::X(x11::get_primary_monitor(connec)),
+        Backend::Error(_) => MonitorID::None,
     }
 }
 
@@ -92,21 +101,24 @@ impl MonitorID {
     pub fn get_name(&self) -> Option<String> {
         match self {
             &MonitorID::X(ref m) => m.get_name(),
-            &MonitorID::Wayland(ref m) => m.get_name()
+            &MonitorID::Wayland(ref m) => m.get_name(),
+            &MonitorID::None => None,
         }
     }
 
     pub fn get_native_identifier(&self) -> ::native_monitor::NativeMonitorId {
         match self {
             &MonitorID::X(ref m) => m.get_native_identifier(),
-            &MonitorID::Wayland(ref m) => m.get_native_identifier()
+            &MonitorID::Wayland(ref m) => m.get_native_identifier(),
+            &MonitorID::None => unimplemented!()        // FIXME: 
         }
     }
 
     pub fn get_dimensions(&self) -> (u32, u32) {
         match self {
             &MonitorID::X(ref m) => m.get_dimensions(),
-            &MonitorID::Wayland(ref m) => m.get_dimensions()
+            &MonitorID::Wayland(ref m) => m.get_dimensions(),
+            &MonitorID::None => (800, 600),     // FIXME: 
         }
     }
 }
@@ -153,6 +165,7 @@ impl Window {
         match *BACKEND {
             Backend::Wayland => wayland::Window::new(builder).map(Window::Wayland),
             Backend::X(ref connec) => x11::Window::new(connec, builder).map(Window::X),
+            Backend::Error(ref error) => Err(CreationError::NoBackendAvailable(Box::new(error.clone())))
         }
     }