don't use futures-executor when it's not the default executor

futures/src/backend/native/async_std.rs

@@ -13,6 +13,10 @@ 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

@@ -12,6 +12,10 @@ 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

@@ -11,6 +11,10 @@ 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

@@ -17,6 +17,13 @@ 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

@@ -14,6 +14,12 @@ impl crate::Executor for Executor {
 
     #[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) {}
 }
 
 pub mod time {

futures/src/backend/wasm/wasm_bindgen.rs

@@ -12,6 +12,10 @@ 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 {

futures/src/executor.rs

@@ -20,4 +20,7 @@ pub trait Executor: Sized {
     fn enter<R>(&self, f: impl FnOnce() -> R) -> R {
         f()
     }
+
+    /// Runs the future on the current thread, blocking it until it is completed.
+    fn block_on(future: impl Future<Output = ()> + 'static);
 }