Allow OSX WindowBuilder to specify 'activation behavior'.

src/os/macos.rs

@@ -1,7 +1,9 @@
 #![cfg(target_os = "macos")]
 
+use std::convert::From;
 use std::os::raw::c_void;
-use Window;
+use cocoa::appkit::NSApplicationActivationPolicy;
+use {Window, WindowBuilder};
 
 /// Additional methods on `Window` that are specific to MacOS.
 pub trait WindowExt {
@@ -17,3 +19,47 @@ impl WindowExt for Window {
         self.window.platform_window() as *mut c_void
     }
 }
+
+/// Corresponds to `NSApplicationActivationPolicy`.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum ActivationPolicy {
+    /// Corresponds to `NSApplicationActivationPolicyRegular`.
+    Regular,
+    /// Corresponds to `NSApplicationActivationPolicyAccessory`.
+    Accessory,
+    /// Corresponds to `NSApplicationActivationPolicyProhibited`.
+    Prohibited,
+}
+
+impl Default for ActivationPolicy {
+    fn default() -> Self {
+        ActivationPolicy::Regular
+    }
+}
+
+impl From<ActivationPolicy> for NSApplicationActivationPolicy {
+    fn from(activation_policy: ActivationPolicy) -> Self {
+        match activation_policy {
+            ActivationPolicy::Regular =>
+                NSApplicationActivationPolicy::NSApplicationActivationPolicyRegular,
+            ActivationPolicy::Accessory =>
+                NSApplicationActivationPolicy::NSApplicationActivationPolicyAccessory,
+            ActivationPolicy::Prohibited =>
+                NSApplicationActivationPolicy::NSApplicationActivationPolicyProhibited,
+        }
+    }
+}
+
+/// Additional methods on `WindowBuilder` that are specific to MacOS.
+pub trait WindowBuilderExt<'a> {
+    fn with_activation_policy(mut self, activation_policy: ActivationPolicy) -> WindowBuilder<'a>;
+}
+
+impl<'a> WindowBuilderExt<'a> for WindowBuilder<'a> {
+    /// Sets the activation policy for the window being built
+    #[inline]
+    fn with_activation_policy(mut self, activation_policy: ActivationPolicy) -> WindowBuilder<'a> {
+        self.platform_specific.activation_policy = activation_policy;
+        self
+    }
+}