Prevent winit from overriding LSUIElement in package manifests (#3920)

src/changelog/unreleased.md

@@ -154,3 +154,5 @@ changelog entry.
 ### Fixed
 
 - On Orbital, `MonitorHandle::name()` now returns `None` instead of a dummy name.
+- On MacOS, package manifest definitions of `LSUIElement` will no longer be overridden with the
+  default activation policy, unless explicitly provided during initialization.

src/platform/macos.rs

@@ -384,9 +384,12 @@ impl WindowAttributesExtMacOS for WindowAttributes {
 }
 
 pub trait EventLoopBuilderExtMacOS {
-    /// Sets the activation policy for the application.
+    /// Sets the activation policy for the application. If used, this will override
+    /// any relevant settings provided in the package manifest.
+    /// For instance, `with_activation_policy(ActivationPolicy::Regular)` will prevent
+    /// the application from running as an "agent", even if LSUIElement is set to true.
     ///
-    /// It is set to [`ActivationPolicy::Regular`] by default.
+    /// If unused, the Winit will honor the package manifest.
     ///
     /// # Example
     ///
@@ -438,7 +441,7 @@ pub trait EventLoopBuilderExtMacOS {
 impl EventLoopBuilderExtMacOS for EventLoopBuilder {
     #[inline]
     fn with_activation_policy(&mut self, activation_policy: ActivationPolicy) -> &mut Self {
-        self.platform_specific.activation_policy = activation_policy;
+        self.platform_specific.activation_policy = Some(activation_policy);
         self
     }
 

src/platform_impl/apple/appkit/app_state.rs

@@ -20,7 +20,7 @@ use crate::window::WindowId as RootWindowId;
 #[derive(Debug)]
 pub(super) struct AppState {
     mtm: MainThreadMarker,
-    activation_policy: NSApplicationActivationPolicy,
+    activation_policy: Option<NSApplicationActivationPolicy>,
     default_menu: bool,
     activate_ignoring_other_apps: bool,
     run_loop: RunLoop,
@@ -65,7 +65,7 @@ static GLOBAL: StaticMainThreadBound<OnceCell<Rc<AppState>>> =
 impl AppState {
     pub(super) fn setup_global(
         mtm: MainThreadMarker,
-        activation_policy: NSApplicationActivationPolicy,
+        activation_policy: Option<NSApplicationActivationPolicy>,
         default_menu: bool,
         activate_ignoring_other_apps: bool,
     ) -> Rc<Self> {
@@ -113,7 +113,11 @@ impl AppState {
         // We need to delay setting the activation policy and activating the app
         // until `applicationDidFinishLaunching` has been called. Otherwise the
         // menu bar is initially unresponsive on macOS 10.15.
-        app.setActivationPolicy(self.activation_policy);
+        // If no activation policy is explicitly provided, do not set it at all
+        // to allow the package manifest to define behavior via LSUIElement.
+        if self.activation_policy.is_some() {
+            app.setActivationPolicy(self.activation_policy.unwrap());
+        }
 
         #[allow(deprecated)]
         app.activateIgnoringOtherApps(self.activate_ignoring_other_apps);

src/platform_impl/apple/appkit/event_loop.rs

@@ -190,18 +190,14 @@ pub struct EventLoop {
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub(crate) struct PlatformSpecificEventLoopAttributes {
-    pub(crate) activation_policy: ActivationPolicy,
+    pub(crate) activation_policy: Option<ActivationPolicy>,
     pub(crate) default_menu: bool,
     pub(crate) activate_ignoring_other_apps: bool,
 }
 
 impl Default for PlatformSpecificEventLoopAttributes {
     fn default() -> Self {
-        Self {
-            activation_policy: Default::default(), // Regular
-            default_menu: true,
-            activate_ignoring_other_apps: true,
-        }
+        Self { activation_policy: None, default_menu: true, activate_ignoring_other_apps: true }
     }
 }
 
@@ -223,9 +219,10 @@ impl EventLoop {
         }
 
         let activation_policy = match attributes.activation_policy {
-            ActivationPolicy::Regular => NSApplicationActivationPolicy::Regular,
-            ActivationPolicy::Accessory => NSApplicationActivationPolicy::Accessory,
-            ActivationPolicy::Prohibited => NSApplicationActivationPolicy::Prohibited,
+            None => None,
+            Some(ActivationPolicy::Regular) => Some(NSApplicationActivationPolicy::Regular),
+            Some(ActivationPolicy::Accessory) => Some(NSApplicationActivationPolicy::Accessory),
+            Some(ActivationPolicy::Prohibited) => Some(NSApplicationActivationPolicy::Prohibited),
         };
 
         let app_state = AppState::setup_global(