Detect unhandled exceptions in async functions without an awaiter

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index b1a0cecead5f373cca55b1bc131180f0851ec71e..2afa616f6275c0232b4a2193d228bcf0056c8dd6 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -939,7 +939,15 @@ const Context& ActivationFrame::GetSavedCurrentContext() {
         OS::PrintErr("\tFound saved current ctx at index %d\n",
                      var_info.index());
       }
-      ctx_ ^= GetStackVar(var_info.index());
+      const Object& obj = Object::Handle(GetStackVar(var_info.index()));
+      if (obj.IsClosure()) {
+        // Closure.call frames.
+        ctx_ ^= Closure::Cast(obj).context();

[rmacnak, 2017/04/12 16:53:03]

The parser is uniformly creating a scope entry for the current context, but
closure invocation is the special case where we're setting it up.

ASSERT(function.name() == Symbols::Call());
ASSERT(function.kind() == kInvokeFieldDispatcher);

+      } else if (obj.IsContext()) {
+        ctx_ ^= Context::Cast(obj).raw();
+      } else {
+        ASSERT(obj.IsNull());
+      }
       return ctx_;
     }
   }
@@ -2049,6 +2057,7 @@ DebuggerStackTrace* Debugger::CollectAwaiterReturnStackTrace() {
           stack_trace->AddActivation(activation);
           // Grab the awaiter.
           async_activation ^= activation->GetAsyncAwaiter();
+          async_stack_trace ^= activation->GetCausalStack();
           break;
         } else {
           stack_trace->AddActivation(CollectDartFrame(
@@ -2058,12 +2067,6 @@ DebuggerStackTrace* Debugger::CollectAwaiterReturnStackTrace() {
     }
   }
 
-  // Return NULL to indicate that there is no useful information in this stack
-  // trace because we never found an awaiter.
-  if (async_activation.IsNull()) {
-    return NULL;
-  }
-
   // Append the awaiter return call stack.
   while (!async_activation.IsNull()) {
     ActivationFrame* activation = new (zone) ActivationFrame(async_activation);