Move common macros into a new crate (fixes #1882)

src/components/macros/macros.rs

@@ -0,0 +1,32 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#[crate_id = "github.com/mozilla/servo#macros:0.1"];
+#[crate_type = "lib"];
+
+#[feature(macro_rules)];
+
+// Spawn a task, capturing the listed variables in a way that avoids the
+// move-from-closure error.  This is sugar around the function spawn_with,
+// taking care of building a tuple and a lambda.
+
+#[macro_export]
+macro_rules! bitfield(
+    ($bitfieldname:ident, $getter:ident, $setter:ident, $value:expr) => (
+        impl $bitfieldname {
+            #[inline]
+            pub fn $getter(self) -> bool {
+                let $bitfieldname(this) = self;
+                (this & $value) != 0
+            }
+
+            #[inline]
+            pub fn $setter(&mut self, value: bool) {
+                let $bitfieldname(this) = *self;
+                *self = $bitfieldname((this & !$value) | (if value { $value } else { 0 }))
+            }
+        }
+    )
+)
+