Move backends behind crate features

Cargo.toml

@@ -8,15 +8,17 @@ license.workspace = true
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[features]
+# Would be nice to have https://github.com/rust-lang/cargo/issues/1197
+default = ["adwaita", "swiftui"]
+adwaita = ["dep:nuit-bridge-adwaita"]
+swiftui = ["dep:nuit-bridge-swiftui"]
+
 [dependencies]
 nuit-derive.workspace = true
 nuit-core.workspace = true
-# TODO: Scope this under not(apple) to avoid pulling it in on macOS?
-# Would be nice to have https://github.com/rust-lang/cargo/issues/1197
-nuit-bridge-adwaita.workspace = true
-
-[target.'cfg(target_vendor = "apple")'.dependencies]
-nuit-bridge-swiftui.workspace = true
+nuit-bridge-adwaita = { workspace = true, optional = true }
+nuit-bridge-swiftui = { workspace = true, optional = true }
 
 [workspace]
 members = [

nuit-bridge-swiftui/rust/lib.rs

@@ -1,5 +1,6 @@
 use nuit_core::CRoot;
 
+#[cfg(target_vendor = "apple")]
 extern "C" {
     pub fn run_app(root: *const CRoot);
 }

src/lib.rs

@@ -8,11 +8,13 @@ pub use nuit_core::*;
 pub use nuit_derive::*;
 
 impl Default for Backend {
+    #[allow(unreachable_code)]
     fn default() -> Self {
-        #[cfg(target_vendor = "apple")]
+        #[cfg(feature = "swiftui")]
         return Backend::SwiftUI;
-        #[cfg(not(target_vendor = "apple"))]
+        #[cfg(feature = "adwaita")]
         return Backend::Adwaita;
+        panic!("A backend must be enabled via Nuit's crate features!");
     }
 }
 
@@ -24,15 +26,19 @@ pub fn run_app<T>(config: impl Into<Config<T>>) where T: View + 'static {
     let root = Root::new(view);
 
     match backend {
+        #[cfg(feature = "swiftui")]
         Backend::SwiftUI => {
             let c_root = CRoot::from(Box::new(root));
             #[cfg(target_vendor = "apple")]
             unsafe { nuit_bridge_swiftui::run_app(&c_root); }
             #[cfg(not(target_vendor = "apple"))]
             panic!("SwiftUI is not supported outside of Apple platforms!")
         }
+        #[cfg(feature = "adwaita")]
         Backend::Adwaita => {
             nuit_bridge_adwaita::run_app(root);
         }
+        #[allow(unreachable_patterns)]
+        _ => panic!("The backend {backend:?} must be enabled via Nuit's crate features!"),
     }
 }