Improvements to causal async stack traces

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 62b9d21d152631168232a70ef5d7ca7a35fc15e1..edd513be8f102022615eaca5633efc2717b4d0b6 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -7060,12 +7060,31 @@ RawString* Function::UserVisibleName() const {
 
 RawString* Function::QualifiedName(NameVisibility name_visibility) const {
   ASSERT(name_visibility != kInternalName);  // We never request it.
+  // If |this| is the generated asynchronous body closure, use the
+  // name of the parent function.
+  Function& fun = Function::Handle(raw());
+  if (fun.IsClosureFunction()) {
+    // Sniff the parent function.
+    fun = fun.parent_function();
+    ASSERT(!fun.IsNull());
+    if (!fun.IsAsyncGenerator() && !fun.IsAsyncFunction() &&
+        !fun.IsSyncGenerator()) {
+      // Parent function is not the generator of an asynchronous body closure,
+      // start at |this|.
+      fun = raw();
+    }
+  }
   // A function's scrubbed name and its user visible name are identical.
-  String& result = String::Handle(UserVisibleName());
+  String& result = String::Handle(fun.UserVisibleName());
   if (IsClosureFunction()) {
-    Function& fun = Function::Handle(raw());
     while (fun.IsLocalFunction() && !fun.IsImplicitClosureFunction()) {
       fun = fun.parent_function();
+      if (fun.IsAsyncClosure() || fun.IsSyncGenClosure() ||
+          fun.IsAsyncGenClosure()) {
+        // Skip the closure and use the real function name found in
+        // the parent.
+        fun = fun.parent_function();
+      }
       result = String::Concat(Symbols::Dot(), result, Heap::kOld);
       result = String::Concat(String::Handle(fun.UserVisibleName()), result,
                               Heap::kOld);
@@ -22418,6 +22437,10 @@ const char* StackTrace::ToCStringInternal(const StackTrace& stack_trace_in,
       } else if (code.raw() ==
                  StubCode::AsynchronousGapMarker_entry()->code()) {
         buffer.AddString("<asynchronous suspension>\n");
+        // The frame immediately after the asynchronous gap marker is the
+        // identical to the frame above the marker. Skip the frame to enhance
+        // the readability of the trace.
+        i++;
       } else {
         ASSERT(code.IsFunctionCode());
         intptr_t pc_offset = Smi::Value(stack_trace.PcOffsetAtFrame(i));