fix build on nightly (rust-lang/rust#45860)

Cargo.toml

@@ -20,6 +20,9 @@ relm = "0.10"
 relm-derive = "0.10"
 shakmaty = "0.4"
 
+[build-dependencies]
+version_check = "0.1"
+
 [dev-dependencies]
 rand = "0.3"
 relm-attributes = "0.10"

build.rs

@@ -0,0 +1,26 @@
+// This file is part of the chessground library.
+// Copyright (C) 2017 Niklas Fiekas <[email protected]>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+extern crate version_check;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    // detect support for nightly features
+    if let Some(true) = version_check::supports_features() {
+        println!("cargo:rustc-cfg=nightly");
+    }
+}

src/boardstate.rs

@@ -16,6 +16,7 @@
 
 use std::f64::consts::PI;
 
+#[cfg(not(nightly))]
 use option_filter::OptionFilterExt;
 
 use cairo::prelude::*;

src/ground.rs

@@ -20,6 +20,7 @@ use std::f64::consts::PI;
 use std::cmp::{min, max};
 use std::fmt;
 
+#[cfg(not(nightly))]
 use option_filter::OptionFilterExt;
 
 use gtk;

src/lib.rs

@@ -20,6 +20,8 @@
 
 #![warn(missing_debug_implementations)]
 
+#![cfg_attr(nightly, feature(option_filter))]
+
 extern crate gtk;
 extern crate gdk;
 extern crate cairo;

src/pieces.rs

@@ -16,6 +16,7 @@
 
 use std::f64::consts::PI;
 
+#[cfg(not(nightly))]
 use option_filter::OptionFilterExt;
 
 use time::SteadyTime;

src/promotable.rs

@@ -16,6 +16,7 @@
 
 use std::f64::consts::PI;
 
+#[cfg(not(nightly))]
 use option_filter::OptionFilterExt;
 
 use time::SteadyTime;