Remove Executor::block_on and simplify Compositor creation

futures/src/backend/native/async_std.rs

@@ -13,10 +13,6 @@ impl crate::Executor for Executor {
     fn spawn(&self, future: impl Future<Output = ()> + Send + 'static) {
         let _ = async_std::task::spawn(future);
     }
-
-    fn block_on(future: impl Future<Output = ()> + 'static) {
-        async_std::task::block_on(future);
-    }
 }
 
 pub mod time {

futures/src/backend/native/smol.rs

@@ -12,10 +12,6 @@ impl crate::Executor for Executor {
     fn spawn(&self, future: impl Future<Output = ()> + Send + 'static) {
         smol::spawn(future).detach();
     }
-
-    fn block_on(future: impl Future<Output = ()> + 'static) {
-        smol::block_on(future);
-    }
 }
 
 pub mod time {

futures/src/backend/native/thread_pool.rs

@@ -11,10 +11,6 @@ impl crate::Executor for Executor {
     fn spawn(&self, future: impl Future<Output = ()> + Send + 'static) {
         self.spawn_ok(future);
     }
-
-    fn block_on(future: impl Future<Output = ()> + 'static) {
-        futures::executor::block_on(future);
-    }
 }
 
 pub mod time {

futures/src/backend/native/tokio.rs

@@ -17,13 +17,6 @@ impl crate::Executor for Executor {
         let _guard = tokio::runtime::Runtime::enter(self);
         f()
     }
-
-    fn block_on(future: impl Future<Output = ()> + 'static) {
-        tokio::runtime::Builder::new_current_thread()
-            .build()
-            .unwrap()
-            .block_on(future);
-    }
 }
 
 pub mod time {

futures/src/backend/null.rs

@@ -1,4 +1,5 @@
 //! A backend that does nothing!
+use crate::MaybeSend;
 
 /// An executor that drops all the futures, instead of spawning them.
 #[derive(Debug)]
@@ -9,17 +10,7 @@ impl crate::Executor for Executor {
         Ok(Self)
     }
 
-    #[cfg(not(target_arch = "wasm32"))]
-    fn spawn(&self, _future: impl Future<Output = ()> + Send + 'static) {}
-
-    #[cfg(target_arch = "wasm32")]
-    fn spawn(&self, _future: impl Future<Output = ()> + 'static) {}
-
-    #[cfg(not(target_arch = "wasm32"))]
-    fn block_on(_future: impl Future<Output = ()> + 'static) {}
-
-    #[cfg(target_arch = "wasm32")]
-    fn block_on(_future: impl Future<Output = ()> + 'static) {}
+    fn spawn(&self, _future: impl Future<Output = ()> + MaybeSend + 'static) {}
 }
 
 pub mod time {

futures/src/backend/wasm/wasm_bindgen.rs

@@ -12,10 +12,6 @@ impl crate::Executor for Executor {
     fn spawn(&self, future: impl futures::Future<Output = ()> + 'static) {
         wasm_bindgen_futures::spawn_local(future);
     }
-
-    fn block_on(future: impl futures::Future<Output = ()> + 'static) {
-        wasm_bindgen_futures::spawn_local(future);
-    }
 }
 
 pub mod time {