Another fix for debugging stack traces and captured variables.

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
===================================================================
--- runtime/vm/debugger.cc	(revision 22155)
+++ runtime/vm/debugger.cc	(working copy)
@@ -339,13 +339,15 @@
 }
 
 
-RawContext* ActivationFrame::GetSavedContext(const Context& ctx) {
+// Get the caller's context, or return ctx if the function does not
+// save the caller's context on entry.
+RawContext* ActivationFrame::GetSavedCallerContext(const Context& ctx) {
   GetVarDescriptors();
   intptr_t var_desc_len = var_descriptors_.Length();
   for (int i = 0; i < var_desc_len; i++) {
     RawLocalVarDescriptors::VarInfo var_info;
     var_descriptors_.GetInfo(i, &var_info);
-    if (var_info.kind == RawLocalVarDescriptors::kContextChain) {
+    if (var_info.kind == RawLocalVarDescriptors::kSavedCallerContext) {
       return reinterpret_cast<RawContext*>(GetLocalVarValue(var_info.index));
     }
   }
@@ -353,6 +355,23 @@
 }
 
 
+// Get the saved context if the callee of this activation frame is a
+// closure function.
+RawContext* ActivationFrame::GetSavedCurrentContext() {
+  GetVarDescriptors();
+  intptr_t var_desc_len = var_descriptors_.Length();
+  for (int i = 0; i < var_desc_len; i++) {
+    RawLocalVarDescriptors::VarInfo var_info;
+    var_descriptors_.GetInfo(i, &var_info);
+    if (var_info.kind == RawLocalVarDescriptors::kSavedCurrentContext) {
+      return reinterpret_cast<RawContext*>(GetLocalVarValue(var_info.index));
+    }
+  }
+  UNREACHABLE();
+  return Context::null();
+}
+
+
 ActivationFrame* DebuggerStackTrace::GetHandlerFrame(
     const Instance& exc_obj) const {
   ExceptionHandlers& handlers = ExceptionHandlers::Handle();
@@ -891,15 +910,25 @@
                                                         frame->fp(),
                                                         frame->sp(),
                                                         code);
+      // If this activation frame called a closure, the function has
+      // saved its context before the call.
+      if (stack_trace->Length() > 0) {
+        ActivationFrame* callee_frame =
+            stack_trace->ActivationFrameAt(stack_trace->Length() - 1);
+        if (callee_frame->function().IsClosureFunction()) {
+          ctx = activation->GetSavedCurrentContext();
+        }
+      }
       if (optimized_frame_found || code.is_optimized()) {
         // Set context to null, to avoid returning bad context variable values.
         activation->SetContext(Context::Handle());
         optimized_frame_found = true;
       } else {
         activation->SetContext(ctx);
-        ctx = activation->GetSavedContext(ctx);
       }
       stack_trace->AddActivation(activation);
+      // Get caller's context if this function saved it on entry.
+      ctx = activation->GetSavedCallerContext(ctx);
     } else if (frame->IsEntryFrame()) {
       ctx = reinterpret_cast<EntryFrame*>(frame)->SavedContext();
     }