Add unwind feature flag

tokio/Cargo.toml

@@ -87,6 +87,7 @@ stream = ["futures-core"]
 sync = []
 test-util = []
 time = []
+unwind = []
 
 [dependencies]
 tokio-macros = { version = "0.3.0", path = "../tokio-macros", optional = true }

tokio/src/runtime/task/harness.rs

@@ -86,17 +86,18 @@ where
         // future has been obtained. This also ensures the `*mut T` pointer
         // contains the future (as opposed to the output) and is initialized.
 
-        let res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
-            struct Guard<'a, T: Future, S: Schedule> {
-                core: &'a Core<T, S>,
-            }
+        struct Guard<'a, T: Future, S: Schedule> {
+            core: &'a Core<T, S>,
+        }
 
-            impl<T: Future, S: Schedule> Drop for Guard<'_, T, S> {
-                fn drop(&mut self) {
-                    self.core.drop_future_or_output();
-                }
+        impl<T: Future, S: Schedule> Drop for Guard<'_, T, S> {
+            fn drop(&mut self) {
+                self.core.drop_future_or_output();
             }
+        }
 
+        #[cfg(not(feature = "unwind"))]
+        let res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
             let guard = Guard { core: self.core() };
 
             // If the task is cancelled, avoid polling it, instead signalling it
@@ -113,6 +114,24 @@ where
             }
         }));
 
+        #[cfg(feature = "unwind")]
+        let res = Ok({
+            let guard = Guard { core: self.core() };
+
+            // If the task is cancelled, avoid polling it, instead signalling it
+            // is complete.
+            if snapshot.is_cancelled() {
+                Poll::Ready(Err(JoinError::cancelled()))
+            } else {
+                let res = guard.core.poll(self.header());
+
+                // prevent the guard from dropping the future
+                mem::forget(guard);
+
+                res.map(Ok)
+            }
+        });
+
         match res {
             Ok(Poll::Ready(out)) => {
                 self.complete(out, snapshot.is_join_interested());

tokio/tests/panics.rs

@@ -0,0 +1,18 @@
+#[cfg(feature = "unwind")]
+#[tokio::test]
+#[should_panic]
+async fn panic_propagated() {
+    tokio::spawn(async {
+        panic!();
+    });
+    tokio::task::yield_now().await;
+}
+
+#[cfg(not(feature = "unwind"))]
+#[tokio::test]
+async fn panic_not_propagated() {
+    tokio::spawn(async {
+        panic!();
+    });
+    tokio::task::yield_now().await;
+}

tokio/tests/process_issue_2174.rs

@@ -16,6 +16,7 @@ use tokio::process::Command;
 use tokio::time;
 use tokio_test::assert_err;
 
+#[cfg(not(feature = "unwind"))]
 #[tokio::test]
 async fn issue_2174() {
     let mut child = Command::new("sleep")

tokio/tests/rt_common.rs

@@ -646,6 +646,7 @@ rt_test! {
         assert_err!(rx.try_recv());
     }
 
+    #[cfg(not(feature = "unwind"))]
     #[test]
     fn panic_in_task() {
         let rt = rt();