Provide better ToCString description for closures (issue 2680).

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 "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
@@ skipping 8920 matching lines @@
   raw_ptr()->context_ = value.raw();
 }
 
 
 void Closure::set_function(const Function& value) const {
   raw_ptr()->function_ = value.raw();
 }
 
 
 const char* Closure::ToCString() const {
-  return "Closure";
+  const Function& fun = Function::Handle(function());
+  const bool is_implicit_closure = fun.IsImplicitClosureFunction();
+  const char* fun_sig = String::Handle(fun.Signature()).ToCString();
+  const char* from = is_implicit_closure ? " from " : "";
+  const char* fun_desc = is_implicit_closure ? fun.ToCString() : "";
+  const char* format = "Closure: %s%s%s";
+  intptr_t len = OS::SNPrint(NULL, 0, format, fun_sig, from, fun_desc) + 1;
+  char* chars = reinterpret_cast<char*>(
+      Isolate::Current()->current_zone()->Allocate(len));
+  OS::SNPrint(chars, len, format, fun_sig, from, fun_desc);
+  return chars;
 }
 
 
 intptr_t Stacktrace::Length() const {
   const Array& code_array = Array::Handle(raw_ptr()->code_array_);
   return code_array.Length();
 }
 
 
 RawFunction* Stacktrace::FunctionAtFrame(intptr_t frame_index) const {
@@ skipping 258 matching lines @@
   const String& str = String::Handle(pattern());
   const char* format = "JSRegExp: pattern=%s flags=%s";
   intptr_t len = OS::SNPrint(NULL, 0, format, str.ToCString(), Flags());
   char* chars = reinterpret_cast<char*>(
       Isolate::Current()->current_zone()->Allocate(len + 1));
   OS::SNPrint(chars, (len + 1), format, str.ToCString(), Flags());
   return chars;
 }
 
 }  // namespace dart