Reland improvements to causal async stack traces

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 7046 matching lines @@
 RawString* Function::UserVisibleName() const {
   if (FLAG_show_internal_names) {
     return name();
   }
   return String::ScrubName(String::Handle(name()));
 }
 
 
 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);
     }
   }
   const Class& cls = Class::Handle(Owner());
   if (!cls.IsTopLevel()) {
     result = String::Concat(Symbols::Dot(), result, Heap::kOld);
     const String& cls_name = String::Handle(name_visibility == kScrubbedName
                                                 ? cls.ScrubbedName()
@@ skipping 15387 matching lines @@
         if ((i < (stack_trace.Length() - 1)) &&
             (stack_trace.CodeAtFrame(i + 1) != Code::null())) {
           buffer.AddString("...\n...\n");
           ASSERT(stack_trace.PcOffsetAtFrame(i) != Smi::null());
           // To account for gap frames.
           (*frame_index) += Smi::Value(stack_trace.PcOffsetAtFrame(i));
         }
       } 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));
         if (code.is_optimized() && stack_trace.expand_inlined()) {
           code.GetInlinedFunctionsAtReturnAddress(pc_offset, &inlined_functions,
                                                   &inlined_token_positions);
           ASSERT(inlined_functions.length() >= 1);
           for (intptr_t j = inlined_functions.length() - 1; j >= 0; j--) {
             if (inlined_functions[j]->is_visible() ||
                 FLAG_show_invisible_frames) {
@@ skipping 336 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart