harmony_scoping: Implement lexical bindings at top level

src/contexts.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/bootstrapper.h"
 #include "src/debug.h"
 #include "src/scopeinfo.h"
 
 namespace v8 {
 namespace internal {
 
+
+Handle<GlobalContextTable> GlobalContextTable::Extend(
+    Handle<GlobalContextTable> table, Handle<Context> global_context) {
+  Isolate* isolate = global_context->GetIsolate();
+  Handle<GlobalContextTable> result;
+  if (table.is_null()) {
+    result = isolate->factory()->NewGlobalContextTable(1);
+  } else {
+    int length = table->length();
+    result = Handle<GlobalContextTable>::cast(
+        FixedArray::CopySize(table, length + 1));

[rossberg, 2014/11/06 12:29:12]

This should perhaps double the table size, pre-allocating some slots.

[Dmitry Lomov (no reviews), 2014/11/06 17:26:58]

Done.

+  }
+  DCHECK(global_context->IsGlobalContext());
+  result->set(result->size() - 1, *global_context);
+  return result;
+}
+
+
+bool GlobalContextTable::Lookup(Handle<GlobalContextTable> table,
+                                Handle<String> name, LookupResult* result) {
+  for (int i = 0; i < table->size(); i++) {
+    Handle<Context> context = GetContext(table, i);
+    DCHECK(context->IsGlobalContext());
+    Handle<ScopeInfo> scope_info(ScopeInfo::cast(context->extension()));
+    int slot_index = ScopeInfo::ContextSlotIndex(
+        scope_info, name, &result->mode_, &result->init_flag_,
+        &result->maybe_assigned_flag_);
+
+    if (slot_index >= 0) {
+      result->context_index_ = i;
+      result->slot_index_ = slot_index;
+      return true;
+    }
+  }
+  return false;
+}
+
+
 Context* Context::declaration_context() {
   Context* current = this;
   while (!current->IsFunctionContext() && !current->IsNativeContext()) {
     current = current->previous();
     DCHECK(current->closure() == closure());
   }
   return current;
 }
 
 
@@ skipping 71 matching lines @@
   Maybe<bool> blacklist = JSReceiver::HasProperty(
       Handle<JSReceiver>::cast(unscopables), it->name());
   if (!blacklist.has_value) {
     DCHECK(isolate->has_pending_exception());
     return Maybe<PropertyAttributes>();
   }
   if (blacklist.value) return maybe(ABSENT);
   return attrs;
 }
 
+static void GetAttributesAndBindingFlags(VariableMode mode,
+                                         InitializationFlag init_flag,
+                                         PropertyAttributes* attributes,
+                                         BindingFlags* binding_flags) {
+  // Note: Fixed context slots are statically allocated by the compiler.

[rossberg, 2014/11/06 12:29:12]

Nit: why not move this comment next to the UNREACHABLE below?

+  // Statically allocated variables always have a statically known mode,
+  // which is the mode with which they were declared when added to the
+  // scope. Thus, the DYNAMIC mode (which corresponds to dynamically
+  // declared variables that were introduced through declaration nodes)
+  // must not appear here.
+  switch (mode) {
+    case INTERNAL:  // Fall through.
+    case VAR:
+      *attributes = NONE;
+      *binding_flags = MUTABLE_IS_INITIALIZED;
+      break;
+    case LET:
+      *attributes = NONE;
+      *binding_flags = (init_flag == kNeedsInitialization)
+                           ? MUTABLE_CHECK_INITIALIZED
+                           : MUTABLE_IS_INITIALIZED;
+      break;
+    case CONST_LEGACY:
+      *attributes = READ_ONLY;
+      *binding_flags = (init_flag == kNeedsInitialization)
+                           ? IMMUTABLE_CHECK_INITIALIZED
+                           : IMMUTABLE_IS_INITIALIZED;
+      break;
+    case CONST:
+      *attributes = READ_ONLY;
+      *binding_flags = (init_flag == kNeedsInitialization)
+                           ? IMMUTABLE_CHECK_INITIALIZED_HARMONY
+                           : IMMUTABLE_IS_INITIALIZED_HARMONY;
+      break;
+    case MODULE:
+      *attributes = READ_ONLY;
+      *binding_flags = IMMUTABLE_IS_INITIALIZED_HARMONY;
+      break;
+    case DYNAMIC:
+    case DYNAMIC_GLOBAL:
+    case DYNAMIC_LOCAL:
+    case TEMPORARY:
+      UNREACHABLE();
+      break;
+  }
+}
+
 
 Handle<Object> Context::Lookup(Handle<String> name,
                                ContextLookupFlags flags,
                                int* index,
                                PropertyAttributes* attributes,
                                BindingFlags* binding_flags) {
   Isolate* isolate = GetIsolate();
   Handle<Context> context(this, isolate);
 
   bool follow_context_chain = (flags & FOLLOW_CONTEXT_CHAIN) != 0;
   *index = -1;
   *attributes = ABSENT;
   *binding_flags = MISSING_BINDING;
 
   if (FLAG_trace_contexts) {
     PrintF("Context::Lookup(");
     name->ShortPrint();
     PrintF(")\n");
   }
 
-  bool visited_global_context = false;
-
   do {
     if (FLAG_trace_contexts) {
       PrintF(" - looking in context %p", reinterpret_cast<void*>(*context));
       if (context->IsGlobalContext()) PrintF(" (global context)");
       if (context->IsNativeContext()) PrintF(" (native context)");
       PrintF("\n");
     }
 
-    if (follow_context_chain && FLAG_harmony_scoping &&
-        !visited_global_context &&
-        (context->IsGlobalContext() || context->IsNativeContext())) {
-      // For lexical scoping, on a top level, we might resolve to the
-      // lexical bindings introduced by later scrips. Therefore we need to
-      // switch to the the last added global context during lookup here.
-      context = Handle<Context>(context->global_object()->global_context());
-      visited_global_context = true;
-      if (FLAG_trace_contexts) {
-        PrintF("   - switching to current global context %p\n",
-               reinterpret_cast<void*>(*context));
-      }
-    }
 
     // 1. Check global objects, subjects of with, and extension objects.
     if (context->IsNativeContext() ||
         context->IsWithContext() ||
         (context->IsFunctionContext() && context->has_extension())) {
       Handle<JSReceiver> object(
           JSReceiver::cast(context->extension()), isolate);
+
+      if (context->IsNativeContext()) {
+        if (FLAG_trace_contexts) {
+          PrintF(" - trying other global contexts\n");
+        }
+        // Try other global contexts.
+        Handle<GlobalContextTable> global_contexts(
+            context->global_object()->native_context()->global_context_table());
+        GlobalContextTable::LookupResult r;
+        if (GlobalContextTable::Lookup(global_contexts, name, &r)) {
+          if (FLAG_trace_contexts) {
+            Handle<Context> c = GlobalContextTable::GetContext(
+                global_contexts, r.context_index_);
+            PrintF("=> found property in global context %d: %p\n",
+                   r.context_index_, reinterpret_cast<void*>(*c));
+          }
+          *index = r.slot_index_;
+          GetAttributesAndBindingFlags(r.mode_, r.init_flag_, attributes,
+                                       binding_flags);
+          return GlobalContextTable::GetContext(global_contexts,
+                                                r.context_index_);
+        }
+      }
+
       // Context extension objects needs to behave as if they have no
       // prototype.  So even if we want to follow prototype chains, we need
       // to only do a local lookup for context extension objects.
       Maybe<PropertyAttributes> maybe;
       if ((flags & FOLLOW_PROTOTYPE_CHAIN) == 0 ||
           object->IsJSContextExtensionObject()) {
         maybe = JSReceiver::GetOwnPropertyAttributes(object, name);
       } else if (context->IsWithContext()) {
         LookupIterator it(object, name);
         maybe = UnscopableLookup(&it);
@@ skipping 34 matching lines @@
       MaybeAssignedFlag maybe_assigned_flag;
       int slot_index = ScopeInfo::ContextSlotIndex(
           scope_info, name, &mode, &init_flag, &maybe_assigned_flag);
       DCHECK(slot_index < 0 || slot_index >= MIN_CONTEXT_SLOTS);
       if (slot_index >= 0) {
         if (FLAG_trace_contexts) {
           PrintF("=> found local in context slot %d (mode = %d)\n",
                  slot_index, mode);
         }
         *index = slot_index;
-        // Note: Fixed context slots are statically allocated by the compiler.
-        // Statically allocated variables always have a statically known mode,
-        // which is the mode with which they were declared when added to the
-        // scope. Thus, the DYNAMIC mode (which corresponds to dynamically
-        // declared variables that were introduced through declaration nodes)
-        // must not appear here.
-        switch (mode) {
-          case INTERNAL:  // Fall through.
-          case VAR:
-            *attributes = NONE;
-            *binding_flags = MUTABLE_IS_INITIALIZED;
-            break;
-          case LET:
-            *attributes = NONE;
-            *binding_flags = (init_flag == kNeedsInitialization)
-                ? MUTABLE_CHECK_INITIALIZED : MUTABLE_IS_INITIALIZED;
-            break;
-          case CONST_LEGACY:
-            *attributes = READ_ONLY;
-            *binding_flags = (init_flag == kNeedsInitialization)
-                ? IMMUTABLE_CHECK_INITIALIZED : IMMUTABLE_IS_INITIALIZED;
-            break;
-          case CONST:
-            *attributes = READ_ONLY;
-            *binding_flags = (init_flag == kNeedsInitialization)
-                ? IMMUTABLE_CHECK_INITIALIZED_HARMONY :
-                IMMUTABLE_IS_INITIALIZED_HARMONY;
-            break;
-          case MODULE:
-            *attributes = READ_ONLY;
-            *binding_flags = IMMUTABLE_IS_INITIALIZED_HARMONY;
-            break;
-          case DYNAMIC:
-          case DYNAMIC_GLOBAL:
-          case DYNAMIC_LOCAL:
-          case TEMPORARY:
-            UNREACHABLE();
-            break;
-        }
+        GetAttributesAndBindingFlags(mode, init_flag, attributes,
+                                     binding_flags);
         return context;
       }
 
       // Check the slot corresponding to the intermediate context holding
       // only the function name variable.
       if (follow_context_chain && context->IsFunctionContext()) {
         VariableMode mode;
         int function_index = scope_info->FunctionContextSlotIndex(*name, &mode);
         if (function_index >= 0) {
           if (FLAG_trace_contexts) {
@@ skipping 169 matching lines @@
 bool Context::IsBootstrappingOrGlobalObject(Isolate* isolate, Object* object) {
   // During bootstrapping we allow all objects to pass as global
   // objects. This is necessary to fix circular dependencies.
   return isolate->heap()->gc_state() != Heap::NOT_IN_GC ||
       isolate->bootstrapper()->IsActive() ||
       object->IsGlobalObject();
 }
 #endif
 
 } }  // namespace v8::internal