Avoid exposing compiler-allocated temporaries to the debugger

src/runtime.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 11181 matching lines @@
   // Check for constructor frame.
   bool constructor = frame_inspector.IsConstructor();
 
   // Get scope info and read from it for local variable information.
   Handle<JSFunction> function(JSFunction::cast(frame_inspector.GetFunction()));
   Handle<SharedFunctionInfo> shared(function->shared());
   Handle<ScopeInfo> scope_info(shared->scope_info());
   ASSERT(*scope_info != ScopeInfo::Empty(isolate));
 
   // Get the locals names and values into a temporary array.
-  //
-  // TODO(1240907): Hide compiler-introduced stack variables
-  // (e.g. .result)?  For users of the debugger, they will probably be
-  // confusing.
+  int local_count = scope_info->LocalCount();
+  for (int slot = 0; slot < scope_info->LocalCount(); ++slot) {
+    // Hide compiler-introduced temporary variables, whether on the stack or on
+    // the context.
+    if (scope_info->LocalIsSynthetic(slot))
+      local_count--;
+  }
+
   Handle<FixedArray> locals =
-      isolate->factory()->NewFixedArray(scope_info->LocalCount() * 2);
+      isolate->factory()->NewFixedArray(local_count * 2);
 
   // Fill in the values of the locals.
+  int local = 0;
   int i = 0;
   for (; i < scope_info->StackLocalCount(); ++i) {
     // Use the value from the stack.
-    locals->set(i * 2, scope_info->LocalName(i));
-    locals->set(i * 2 + 1, frame_inspector.GetExpression(i));
+    if (scope_info->LocalIsSynthetic(i))
+      continue;
+    locals->set(local * 2, scope_info->LocalName(i));
+    locals->set(local * 2 + 1, frame_inspector.GetExpression(i));
+    local++;
   }
-  if (i < scope_info->LocalCount()) {
+  if (local < local_count) {
     // Get the context containing declarations.
     Handle<Context> context(
         Context::cast(it.frame()->context())->declaration_context());
     for (; i < scope_info->LocalCount(); ++i) {
+      if (scope_info->LocalIsSynthetic(i))
+        continue;
       Handle<String> name(scope_info->LocalName(i));
       VariableMode mode;
       InitializationFlag init_flag;
-      locals->set(i * 2, *name);
+      locals->set(local * 2, *name);
       int context_slot_index =
           scope_info->ContextSlotIndex(*name, &mode, &init_flag);
       Object* value = context->get(context_slot_index);
-      locals->set(i * 2 + 1, value);
+      locals->set(local * 2 + 1, value);
+      local++;
     }
   }
 
   // Check whether this frame is positioned at return. If not top
   // frame or if the frame is optimized it cannot be at a return.
   bool at_return = false;
   if (!is_optimized && index == 0) {
     at_return = isolate->debug()->IsBreakAtReturn(it.frame());
   }
 
@@ skipping 40 matching lines @@
 
   // Find the number of arguments to fill. At least fill the number of
   // parameters for the function and fill more if more parameters are provided.
   int argument_count = scope_info->ParameterCount();
   if (argument_count < frame_inspector.GetParametersCount()) {
     argument_count = frame_inspector.GetParametersCount();
   }
 
   // Calculate the size of the result.
   int details_size = kFrameDetailsFirstDynamicIndex +
-                     2 * (argument_count + scope_info->LocalCount()) +
+                     2 * (argument_count + local_count) +
                      (at_return ? 1 : 0);
   Handle<FixedArray> details = isolate->factory()->NewFixedArray(details_size);
 
   // Add the frame id.
   details->set(kFrameDetailsFrameIdIndex, *frame_id);
 
   // Add the function (same as in function frame).
   details->set(kFrameDetailsFunctionIndex, frame_inspector.GetFunction());
 
   // Add the arguments count.
   details->set(kFrameDetailsArgumentCountIndex, Smi::FromInt(argument_count));
 
   // Add the locals count
   details->set(kFrameDetailsLocalCountIndex,
-               Smi::FromInt(scope_info->LocalCount()));
+               Smi::FromInt(local_count));
 
   // Add the source position.
   if (position != RelocInfo::kNoPosition) {
     details->set(kFrameDetailsSourcePositionIndex, Smi::FromInt(position));
   } else {
     details->set(kFrameDetailsSourcePositionIndex, heap->undefined_value());
   }
 
   // Add the constructor information.
   details->set(kFrameDetailsConstructCallIndex, heap->ToBoolean(constructor));
@@ skipping 30 matching lines @@
     // Parameter value.
     if (i < frame_inspector.GetParametersCount()) {
       // Get the value from the stack.
       details->set(details_index++, frame_inspector.GetParameter(i));
     } else {
       details->set(details_index++, heap->undefined_value());
     }
   }
 
   // Add locals name and value from the temporary copy from the function frame.
-  for (int i = 0; i < scope_info->LocalCount() * 2; i++) {
+  for (int i = 0; i < local_count * 2; i++) {
     details->set(details_index++, locals->get(i));
   }
 
   // Add the value being returned.
   if (at_return) {
     details->set(details_index++, *return_value);
   }
 
   // Add the receiver (same as in function frame).
   // THIS MUST BE DONE LAST SINCE WE MIGHT ADVANCE
@@ skipping 60 matching lines @@
     Handle<String> name(scope_info->ParameterName(i));
 
     RETURN_ON_EXCEPTION(
         isolate,
         Runtime::SetObjectProperty(isolate, target, name, value, NONE, SLOPPY),
         JSObject);
   }
 
   // Second fill all stack locals.
   for (int i = 0; i < scope_info->StackLocalCount(); ++i) {
+    if (scope_info->LocalIsSynthetic(i)) continue;
     Handle<String> name(scope_info->StackLocalName(i));
     Handle<Object> value(frame_inspector->GetExpression(i), isolate);
     if (value->IsTheHole()) continue;
 
     RETURN_ON_EXCEPTION(
         isolate,
         Runtime::SetObjectProperty(isolate, target, name, value, NONE, SLOPPY),
         JSObject);
   }
 
@@ skipping 24 matching lines @@
     ASSERT(!frame->GetParameter(i)->IsTheHole());
     HandleScope scope(isolate);
     Handle<String> name(scope_info->ParameterName(i));
     Handle<Object> value =
         Object::GetPropertyOrElement(target, name).ToHandleChecked();
     frame->SetParameterValue(i, *value);
   }
 
   // Stack locals.
   for (int i = 0; i < scope_info->StackLocalCount(); ++i) {
+    if (scope_info->LocalIsSynthetic(i)) continue;
     if (frame->GetExpression(i)->IsTheHole()) continue;
     HandleScope scope(isolate);
     Handle<Object> value = Object::GetPropertyOrElement(
         target,
         handle(scope_info->StackLocalName(i), isolate)).ToHandleChecked();
     frame->SetExpression(i, *value);
   }
 }
 
 
@@ skipping 3641 matching lines @@
   }
 }
 
 
 void Runtime::OutOfMemory() {
   Heap::FatalProcessOutOfMemory("CALL_AND_RETRY_LAST", true);
   UNREACHABLE();
 }
 
 } }  // namespace v8::internal