Vendor dependencies for 0.3.0 release

vendor/bevy_derive/src/bevy_main.rs

@@ -0,0 +1,26 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{parse_macro_input, ItemFn};
+
+pub fn bevy_main(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(item as ItemFn);
+    assert_eq!(
+        input.sig.ident, "main",
+        "`bevy_main` can only be used on a function called 'main'."
+    );
+
+    TokenStream::from(quote! {
+        // SAFETY: `#[bevy_main]` should only be placed on a single `main` function
+        // TODO: Potentially make `bevy_main` and unsafe attribute as there is a safety
+        // guarantee required from the caller.
+        #[unsafe(no_mangle)]
+        #[cfg(target_os = "android")]
+        fn android_main(android_app: bevy::window::android_activity::AndroidApp) {
+            let _ = bevy::window::ANDROID_APP.set(android_app);
+            main();
+        }
+
+        #[allow(unused)]
+        #input
+    })
+}