text: // Copyright 2006-2008 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
  //       with the distribution.
  //     * Neither the name of Google Inc. nor the names of its
  //       contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #ifndef V8_CONTEXTS_H_
  #define V8_CONTEXTS_H_
  
  namespace v8 {
  namespace internal {
  
  
  enum ContextLookupFlags {
    FOLLOW_CONTEXT_CHAIN = 1,
    FOLLOW_PROTOTYPE_CHAIN = 2,
  
    DONT_FOLLOW_CHAINS = 0,
    FOLLOW_CHAINS = FOLLOW_CONTEXT_CHAIN | FOLLOW_PROTOTYPE_CHAIN
  };
  
  
  // Heap-allocated activation contexts.
  //
  // Contexts are implemented as FixedArray objects; the Context
  // class is a convenience interface casted on a FixedArray object.
  //
  // Note: Context must have no virtual functions and Context objects
  // must always be allocated via Heap::AllocateContext() or
  // Factory::NewContext.
  
  // Comment for special_function_table:
  // Table for providing optimized/specialized functions.
  // The array contains triplets [object, general_function, optimized_function].
  // Primarily added to support built-in optimized variants of
  // Array.prototype.{push,pop}.
  
  #define GLOBAL_CONTEXT_FIELDS(V) \
    V(GLOBAL_PROXY_INDEX, JSObject, global_proxy_object) \
    V(SECURITY_TOKEN_INDEX, Object, security_token) \
    V(BOOLEAN_FUNCTION_INDEX, JSFunction, boolean_function) \
    V(NUMBER_FUNCTION_INDEX, JSFunction, number_function) \
    V(STRING_FUNCTION_INDEX, JSFunction, string_function) \
    V(OBJECT_FUNCTION_INDEX, JSFunction, object_function) \
    V(ARRAY_FUNCTION_INDEX, JSFunction, array_function) \
    V(DATE_FUNCTION_INDEX, JSFunction, date_function) \
    V(JSON_OBJECT_INDEX, JSObject, json_object) \
    V(REGEXP_FUNCTION_INDEX, JSFunction, regexp_function) \
    V(INITIAL_OBJECT_PROTOTYPE_INDEX, JSObject, initial_object_prototype) \
    V(CREATE_DATE_FUN_INDEX, JSFunction,  create_date_fun) \
    V(TO_NUMBER_FUN_INDEX, JSFunction, to_number_fun) \
    V(TO_STRING_FUN_INDEX, JSFunction, to_string_fun) \
    V(TO_DETAIL_STRING_FUN_INDEX, JSFunction, to_detail_string_fun) \
    V(TO_OBJECT_FUN_INDEX, JSFunction, to_object_fun) \
    V(TO_INTEGER_FUN_INDEX, JSFunction, to_integer_fun) \
    V(TO_UINT32_FUN_INDEX, JSFunction, to_uint32_fun) \
    V(TO_INT32_FUN_INDEX, JSFunction, to_int32_fun) \
    V(TO_BOOLEAN_FUN_INDEX, JSFunction, to_boolean_fun) \
    V(GLOBAL_EVAL_FUN_INDEX, JSFunction, global_eval_fun) \
    V(INSTANTIATE_FUN_INDEX, JSFunction, instantiate_fun) \
    V(CONFIGURE_INSTANCE_FUN_INDEX, JSFunction, configure_instance_fun) \
    V(FUNCTION_MAP_INDEX, Map, function_map) \
    V(FUNCTION_INSTANCE_MAP_INDEX, Map, function_instance_map) \
    V(JS_ARRAY_MAP_INDEX, Map, js_array_map)\
    V(SPECIAL_FUNCTION_TABLE_INDEX, FixedArray, special_function_table) \
    V(ARGUMENTS_BOILERPLATE_INDEX, JSObject, arguments_boilerplate) \
    V(MESSAGE_LISTENERS_INDEX, JSObject, message_listeners) \
    V(MAKE_MESSAGE_FUN_INDEX, JSFunction, make_message_fun) \
    V(GET_STACK_TRACE_LINE_INDEX, JSFunction, get_stack_trace_line_fun) \
    V(CONFIGURE_GLOBAL_INDEX, JSFunction, configure_global_fun) \
    V(FUNCTION_CACHE_INDEX, JSObject, function_cache) \
    V(RUNTIME_CONTEXT_INDEX, Context, runtime_context) \
    V(CALL_AS_FUNCTION_DELEGATE_INDEX, JSFunction, call_as_function_delegate) \
    V(CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, JSFunction, \
      call_as_constructor_delegate) \
    V(EMPTY_SCRIPT_INDEX, Script, empty_script) \
    V(SCRIPT_FUNCTION_INDEX, JSFunction, script_function) \
    V(CONTEXT_EXTENSION_FUNCTION_INDEX, JSFunction, context_extension_function) \
    V(OUT_OF_MEMORY_INDEX, Object, out_of_memory) \
    V(MAP_CACHE_INDEX, Object, map_cache) \
    V(CONTEXT_DATA_INDEX, Object, data)
  
  // JSFunctions are pairs (context, function code), sometimes also called
  // closures. A Context object is used to represent function contexts and
  // dynamically pushed 'with' contexts (or 'scopes' in ECMA-262 speak).
  //
  // At runtime, the contexts build a stack in parallel to the execution
  // stack, with the top-most context being the current context. All contexts
  // have the following slots:
  //
  // [ closure   ]  This is the current function. It is the same for all
  //                contexts inside a function. It provides access to the
  //                incoming context (i.e., the outer context, which may
  //                or may not become the current function's context), and
  //                it provides access to the functions code and thus it's
  //                scope information, which in turn contains the names of
  //                statically allocated context slots. The names are needed
  //                for dynamic lookups in the presence of 'with' or 'eval'.
  //
  // [ fcontext  ]  A pointer to the innermost enclosing function context.
  //                It is the same for all contexts *allocated* inside a
  //                function, and the function context's fcontext points
  //                to itself. It is only needed for fast access of the
  //                function context (used for declarations, and static
  //                context slot access).
  //
  // [ previous  ]  A pointer to the previous context. It is NULL for
  //                function contexts, and non-NULL for 'with' contexts.
  //                Used to implement the 'with' statement.
  //
  // [ extension ]  A pointer to an extension JSObject, or NULL. Used to
  //                implement 'with' statements and dynamic declarations
  //                (through 'eval'). The object in a 'with' statement is
  //                stored in the extension slot of a 'with' context.
  //                Dynamically declared variables/functions are also added
  //                to lazily allocated extension object. Context::Lookup
  //                searches the extension object for properties.
  //
  // [ global    ]  A pointer to the global object. Provided for quick
  //                access to the global object from inside the code (since
  //                we always have a context pointer).
  //
  // In addition, function contexts may have statically allocated context slots
  // to store local variables/functions that are accessed from inner functions
  // (via static context addresses) or through 'eval' (dynamic context lookups).
  // Finally, the global context contains additional slots for fast access to
  // global properties.
  //
  // We may be able to simplify the implementation:
  //
  // - We may be able to get rid of 'fcontext': We can always use the fact that
  //   previous == NULL for function contexts and so we can search for them. They
  //   are only needed when doing dynamic declarations, and the context chains
  //   tend to be very very short (depth of nesting of 'with' statements). At
  //   the moment we also use it in generated code for context slot accesses -
  //   and there we don't want a loop because of code bloat - but we may not
  //   need it there after all (see comment in codegen_*.cc).
  //
  // - If we cannot get rid of fcontext, consider making 'previous' never NULL
  //   except for the global context. This could simplify Context::Lookup.
  
  class Context: public FixedArray {
   public:
    // Conversions.
    static Context* cast(Object* context) {
      ASSERT(context->IsContext());
      return reinterpret_cast<Context*>(context);
    }
  
    // The default context slot layout; indices are FixedArray slot indices.
    enum {
      // These slots are in all contexts.
      CLOSURE_INDEX,
      FCONTEXT_INDEX,
      PREVIOUS_INDEX,
      EXTENSION_INDEX,
      GLOBAL_INDEX,
      MIN_CONTEXT_SLOTS,
  
      // These slots are only in global contexts.
      GLOBAL_PROXY_INDEX = MIN_CONTEXT_SLOTS,
      SECURITY_TOKEN_INDEX,
      ARGUMENTS_BOILERPLATE_INDEX,
      JS_ARRAY_MAP_INDEX,
      FUNCTION_MAP_INDEX,
      FUNCTION_INSTANCE_MAP_INDEX,
      INITIAL_OBJECT_PROTOTYPE_INDEX,
      BOOLEAN_FUNCTION_INDEX,
      NUMBER_FUNCTION_INDEX,
      STRING_FUNCTION_INDEX,
      OBJECT_FUNCTION_INDEX,
      ARRAY_FUNCTION_INDEX,
      DATE_FUNCTION_INDEX,
      JSON_OBJECT_INDEX,
      REGEXP_FUNCTION_INDEX,
      CREATE_DATE_FUN_INDEX,
      TO_NUMBER_FUN_INDEX,
      TO_STRING_FUN_INDEX,
      TO_DETAIL_STRING_FUN_INDEX,
      TO_OBJECT_FUN_INDEX,
      TO_INTEGER_FUN_INDEX,
      TO_UINT32_FUN_INDEX,
      TO_INT32_FUN_INDEX,
      TO_BOOLEAN_FUN_INDEX,
      GLOBAL_EVAL_FUN_INDEX,
      INSTANTIATE_FUN_INDEX,
      CONFIGURE_INSTANCE_FUN_INDEX,
      SPECIAL_FUNCTION_TABLE_INDEX,
      MESSAGE_LISTENERS_INDEX,
      MAKE_MESSAGE_FUN_INDEX,
      GET_STACK_TRACE_LINE_INDEX,
      CONFIGURE_GLOBAL_INDEX,
      FUNCTION_CACHE_INDEX,
      RUNTIME_CONTEXT_INDEX,
      CALL_AS_FUNCTION_DELEGATE_INDEX,
      CALL_AS_CONSTRUCTOR_DELEGATE_INDEX,
      EMPTY_SCRIPT_INDEX,
      SCRIPT_FUNCTION_INDEX,
      CONTEXT_EXTENSION_FUNCTION_INDEX,
      OUT_OF_MEMORY_INDEX,
      MAP_CACHE_INDEX,
      CONTEXT_DATA_INDEX,
      GLOBAL_CONTEXT_SLOTS
    };
  
    // Direct slot access.
    JSFunction* closure() { return JSFunction::cast(get(CLOSURE_INDEX)); }
    void set_closure(JSFunction* closure) { set(CLOSURE_INDEX, closure); }
  
    Context* fcontext() { return Context::cast(get(FCONTEXT_INDEX)); }
    void set_fcontext(Context* context) { set(FCONTEXT_INDEX, context); }
  
    Context* previous() {
      Object* result = unchecked_previous();
      ASSERT(IsBootstrappingOrContext(result));
      return reinterpret_cast<Context*>(result);
    }
    void set_previous(Context* context) { set(PREVIOUS_INDEX, context); }
  
    bool has_extension() { return unchecked_extension() != NULL; }
    JSObject* extension() { return JSObject::cast(unchecked_extension()); }
    void set_extension(JSObject* object) { set(EXTENSION_INDEX, object); }
  
    GlobalObject* global() {
      Object* result = get(GLOBAL_INDEX);
      ASSERT(IsBootstrappingOrGlobalObject(result));
      return reinterpret_cast<GlobalObject*>(result);
    }
    void set_global(GlobalObject* global) { set(GLOBAL_INDEX, global); }
  
    // Returns a JSGlobalProxy object or null.
    JSObject* global_proxy();
    void set_global_proxy(JSObject* global);
  
    // The builtins object.
    JSBuiltinsObject* builtins();
  
    // Compute the global context by traversing the context chain.
    Context* global_context();
  
    // Tells if this is a function context (as opposed to a 'with' context).
    bool is_function_context() { return unchecked_previous() == NULL; }
  
    // Tells whether the global context is marked with out of memory.
    bool has_out_of_memory() {
      return global_context()->out_of_memory() == Heap::true_value();
    }
  
    // Mark the global context with out of memory.
    void mark_out_of_memory() {
      global_context()->set_out_of_memory(Heap::true_value());
    }
  
    // The exception holder is the object used as a with object in
    // the implementation of a catch block.
    bool is_exception_holder(Object* object) {
      return IsCatchContext() && extension() == object;
    }
  
  #define GLOBAL_CONTEXT_FIELD_ACCESSORS(index, type, name) \
    void  set_##name(type* value) {                         \
      ASSERT(IsGlobalContext());                            \
      set(index, value);                                    \
    }                                                       \
    type* name() {                                          \
      ASSERT(IsGlobalContext());                            \
      return type::cast(get(index));                        \
    }
    GLOBAL_CONTEXT_FIELDS(GLOBAL_CONTEXT_FIELD_ACCESSORS)
  #undef GLOBAL_CONTEXT_FIELD_ACCESSORS
  
    // Lookup the the slot called name, starting with the current context.
    // There are 4 possible outcomes:
    //
    // 1) index_ >= 0 && result->IsContext():
    //    most common case, the result is a Context, and index is the
    //    context slot index, and the slot exists.
    //    attributes == READ_ONLY for the function name variable, NONE otherwise.
    //
    // 2) index_ >= 0 && result->IsJSObject():
    //    the result is the JSObject arguments object, the index is the parameter
    //    index, i.e., key into the arguments object, and the property exists.
    //    attributes != ABSENT.
    //
    // 3) index_ < 0 && result->IsJSObject():
    //    the result is the JSObject extension context or the global object,
    //    and the name is the property name, and the property exists.
    //    attributes != ABSENT.
    //
    // 4) index_ < 0 && result.is_null():
    //    there was no context found with the corresponding property.
    //    attributes == ABSENT.
    Handle<Object> Lookup(Handle<String> name, ContextLookupFlags flags,
                          int* index_, PropertyAttributes* attributes);
  
    // Determine if a local variable with the given name exists in a
    // context.  Do not consider context extension objects.  This is
    // used for compiling code using eval.  If the context surrounding
    // the eval call does not have a local variable with this name and
    // does not contain a with statement the property is global unless
    // it is shadowed by a property in an extension object introduced by
    // eval.
    bool GlobalIfNotShadowedByEval(Handle<String> name);
  
    // Code generation support.
    static int SlotOffset(int index) {
      return kHeaderSize + index * kPointerSize - kHeapObjectTag;
    }
  
   private:
    // Unchecked access to the slots.
    Object* unchecked_previous() { return get(PREVIOUS_INDEX); }
    Object* unchecked_extension() { return get(EXTENSION_INDEX); }
  
  #ifdef DEBUG
    // Bootstrapping-aware type checks.
    static bool IsBootstrappingOrContext(Object* object);
    static bool IsBootstrappingOrGlobalObject(Object* object);
  #endif
  };
  
  } }  // namespace v8::internal
  
  #endif  // V8_CONTEXTS_H_
  