LibJS: Begin implementing GlobalEnvironmentRecord

These represent the outermost scope in the environment record
hierarchy. The spec says they should be a "composite" of two things:

- An ObjectEnvironmentRecord wrapping the global object
- A DeclarativeEnvironmentRecord for other declarations

It's not yet clear to me how this should work, so this patch only
implements the first part, an object record wrapping the global object.

Userland/Libraries/LibJS/Bytecode/Interpreter.cpp

@@ -10,6 +10,7 @@
 #include <LibJS/Bytecode/Instruction.h>
 #include <LibJS/Bytecode/Interpreter.h>
 #include <LibJS/Bytecode/Op.h>
+#include <LibJS/Runtime/GlobalEnvironmentRecord.h>
 #include <LibJS/Runtime/GlobalObject.h>
 
 namespace JS::Bytecode {
@@ -48,7 +49,8 @@ Value Interpreter::run(Executable const& executable, BasicBlock const* entry_poi
         global_call_frame.this_value = &global_object();
         static FlyString global_execution_context_name = "(*BC* global execution context)";
         global_call_frame.function_name = global_execution_context_name;
-        global_call_frame.lexical_environment = &global_object();
+        global_call_frame.lexical_environment = &global_object().environment_record();
+        global_call_frame.variable_environment = &global_object().environment_record();
         VERIFY(!vm().exception());
         // FIXME: How do we know if we're in strict mode? Maybe the Bytecode::Block should know this?
         // global_call_frame.is_strict_mode = ???;

Userland/Libraries/LibJS/CMakeLists.txt

@@ -67,6 +67,7 @@ set(SOURCES
     Runtime/GeneratorFunctionPrototype.cpp
     Runtime/GeneratorObject.cpp
     Runtime/GeneratorObjectPrototype.cpp
+    Runtime/GlobalEnvironmentRecord.cpp
     Runtime/GlobalObject.cpp
     Runtime/IndexedProperties.cpp
     Runtime/IteratorOperations.cpp

Userland/Libraries/LibJS/Forward.h

@@ -129,6 +129,7 @@ class Exception;
 class Expression;
 class FunctionEnvironmentRecord;
 class FunctionNode;
+class GlobalEnvironmentRecord;
 class GlobalObject;
 class HandleImpl;
 class Heap;

Userland/Libraries/LibJS/Interpreter.cpp

@@ -10,6 +10,7 @@
 #include <LibJS/AST.h>
 #include <LibJS/Interpreter.h>
 #include <LibJS/Runtime/FunctionEnvironmentRecord.h>
+#include <LibJS/Runtime/GlobalEnvironmentRecord.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Reference.h>
@@ -50,8 +51,8 @@ void Interpreter::run(GlobalObject& global_object, const Program& program)
     global_call_frame.this_value = &global_object;
     static FlyString global_execution_context_name = "(global execution context)";
     global_call_frame.function_name = global_execution_context_name;
-    global_call_frame.lexical_environment = &global_object;
-    global_call_frame.variable_environment = &global_object;
+    global_call_frame.lexical_environment = &global_object.environment_record();
+    global_call_frame.variable_environment = &global_object.environment_record();
     VERIFY(!vm.exception());
     global_call_frame.is_strict_mode = program.is_strict_mode();
     vm.push_call_frame(global_call_frame, global_object);

Userland/Libraries/LibJS/Runtime/EnvironmentRecord.cpp

@@ -15,11 +15,6 @@ EnvironmentRecord::EnvironmentRecord(EnvironmentRecord* outer_environment)
 {
 }
 
-EnvironmentRecord::EnvironmentRecord(GlobalObjectTag tag)
-    : Object(tag)
-{
-}
-
 void EnvironmentRecord::visit_edges(Visitor& visitor)
 {
     Base::visit_edges(visitor);

Userland/Libraries/LibJS/Runtime/EnvironmentRecord.h

@@ -32,7 +32,6 @@ public:
 
 protected:
     explicit EnvironmentRecord(EnvironmentRecord* parent);
-    explicit EnvironmentRecord(GlobalObjectTag);
 
     virtual void visit_edges(Visitor&) override;
 

Userland/Libraries/LibJS/Runtime/GlobalEnvironmentRecord.cpp

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/AST.h>
+#include <LibJS/Runtime/DeclarativeEnvironmentRecord.h>
+#include <LibJS/Runtime/GlobalEnvironmentRecord.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/ObjectEnvironmentRecord.h>
+
+namespace JS {
+
+GlobalEnvironmentRecord::GlobalEnvironmentRecord(GlobalObject& global_object)
+    : EnvironmentRecord(nullptr)
+    , m_global_object(global_object)
+{
+    m_object_record = global_object.heap().allocate<ObjectEnvironmentRecord>(global_object, global_object, nullptr);
+    m_declarative_record = global_object.heap().allocate<DeclarativeEnvironmentRecord>(global_object);
+}
+
+void GlobalEnvironmentRecord::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_object_record);
+    visitor.visit(m_declarative_record);
+}
+
+Optional<Variable> GlobalEnvironmentRecord::get_from_environment_record(FlyString const& name) const
+{
+    // FIXME: This should be a "composite" of the object record and the declarative record.
+    return m_object_record->get_from_environment_record(name);
+}
+
+void GlobalEnvironmentRecord::put_into_environment_record(FlyString const& name, Variable variable)
+{
+    // FIXME: This should be a "composite" of the object record and the declarative record.
+    m_object_record->put_into_environment_record(name, variable);
+}
+
+bool GlobalEnvironmentRecord::delete_from_environment_record(FlyString const& name)
+{
+    // FIXME: This should be a "composite" of the object record and the declarative record.
+    return object_record().delete_property(name);
+}
+
+Value GlobalEnvironmentRecord::get_this_binding(GlobalObject&) const
+{
+    return &m_global_object;
+}
+
+Value GlobalEnvironmentRecord::global_this_value() const
+{
+    return &m_global_object;
+}
+
+}

Userland/Libraries/LibJS/Runtime/GlobalEnvironmentRecord.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/EnvironmentRecord.h>
+
+namespace JS {
+
+class GlobalEnvironmentRecord final : public EnvironmentRecord {
+    JS_OBJECT(GlobalEnvironmentRecord, EnvironmentRecord);
+
+public:
+    explicit GlobalEnvironmentRecord(GlobalObject&);
+
+    virtual Optional<Variable> get_from_environment_record(FlyString const&) const override;
+    virtual void put_into_environment_record(FlyString const&, Variable) override;
+    virtual bool delete_from_environment_record(FlyString const&) override;
+    virtual bool has_this_binding() const final { return true; }
+    virtual Value get_this_binding(GlobalObject&) const final;
+
+    Value global_this_value() const;
+
+    // [[ObjectRecord]]
+    ObjectEnvironmentRecord& object_record() { return *m_object_record; }
+
+    // [[DeclarativeReco rd]]
+    DeclarativeEnvironmentRecord& declarative_record() { return *m_declarative_record; }
+
+private:
+    virtual bool is_global_environment_record() const override { return true; }
+    virtual void visit_edges(Visitor&) override;
+
+    GlobalObject& m_global_object;
+
+    ObjectEnvironmentRecord* m_object_record { nullptr };
+    DeclarativeEnvironmentRecord* m_declarative_record { nullptr };
+};
+
+template<>
+inline bool Object::fast_is<GlobalEnvironmentRecord>() const { return is_global_environment_record(); }
+
+}

Userland/Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -40,6 +40,7 @@
 #include <LibJS/Runtime/GeneratorFunctionConstructor.h>
 #include <LibJS/Runtime/GeneratorFunctionPrototype.h>
 #include <LibJS/Runtime/GeneratorObjectPrototype.h>
+#include <LibJS/Runtime/GlobalEnvironmentRecord.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/IteratorPrototype.h>
 #include <LibJS/Runtime/JSONObject.h>
@@ -82,7 +83,7 @@
 namespace JS {
 
 GlobalObject::GlobalObject()
-    : EnvironmentRecord(GlobalObjectTag::Tag)
+    : Object(GlobalObjectTag::Tag)
     , m_console(make<Console>(*this))
 {
 }
@@ -98,6 +99,8 @@ void GlobalObject::initialize_global_object()
     m_object_prototype = heap().allocate_without_global_object<ObjectPrototype>(*this);
     m_function_prototype = heap().allocate_without_global_object<FunctionPrototype>(*this);
 
+    m_environment_record = heap().allocate_without_global_object<GlobalEnvironmentRecord>(*this);
+
     m_new_object_shape = vm.heap().allocate_without_global_object<Shape>(*this);
     m_new_object_shape->set_prototype_without_transition(m_object_prototype);
 
@@ -207,6 +210,7 @@ void GlobalObject::visit_edges(Visitor& visitor)
     visitor.visit(m_new_script_function_prototype_object_shape);
     visitor.visit(m_proxy_constructor);
     visitor.visit(m_generator_object_prototype);
+    visitor.visit(m_environment_record);
 
 #define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, ArrayType) \
     visitor.visit(m_##snake_name##_constructor);                                         \
@@ -328,24 +332,6 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::parse_int)
     return Value(sign * number);
 }
 
-Optional<Variable> GlobalObject::get_from_environment_record(FlyString const& name) const
-{
-    auto value = get(name);
-    if (value.is_empty())
-        return {};
-    return Variable { value, DeclarationKind::Var };
-}
-
-void GlobalObject::put_into_environment_record(FlyString const& name, Variable variable)
-{
-    put(name, variable.value);
-}
-
-bool GlobalObject::delete_from_environment_record(FlyString const& name)
-{
-    return delete_property(name);
-}
-
 // 19.2.1 eval ( x ), https://tc39.es/ecma262/#sec-eval-x
 JS_DEFINE_NATIVE_FUNCTION(GlobalObject::eval)
 {

Userland/Libraries/LibJS/Runtime/GlobalObject.h

@@ -12,8 +12,8 @@
 
 namespace JS {
 
-class GlobalObject : public EnvironmentRecord {
-    JS_OBJECT(GlobalObject, EnvironmentRecord);
+class GlobalObject : public Object {
+    JS_OBJECT(GlobalObject, Object);
 
 public:
     explicit GlobalObject();
@@ -21,11 +21,7 @@ public:
 
     virtual ~GlobalObject() override;
 
-    virtual Optional<Variable> get_from_environment_record(FlyString const&) const override;
-    virtual void put_into_environment_record(FlyString const&, Variable) override;
-    virtual bool delete_from_environment_record(FlyString const&) override;
-    virtual bool has_this_binding() const final { return true; }
-    virtual Value get_this_binding(GlobalObject&) const final { return this; }
+    GlobalEnvironmentRecord& environment_record() { return *m_environment_record; }
 
     Console& console() { return *m_console; }
 
@@ -87,6 +83,8 @@ private:
     // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct constructor
     GeneratorObjectPrototype* m_generator_object_prototype { nullptr };
 
+    GlobalEnvironmentRecord* m_environment_record { nullptr };
+
 #define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, ArrayType) \
     ConstructorName* m_##snake_name##_constructor { nullptr };                           \
     Object* m_##snake_name##_prototype { nullptr };

Userland/Libraries/LibJS/Runtime/Object.h

@@ -108,6 +108,7 @@ public:
     virtual bool is_global_object() const { return false; }
     virtual bool is_proxy_object() const { return false; }
     virtual bool is_native_function() const { return false; }
+    virtual bool is_global_environment_record() const { return false; }
     virtual bool is_declarative_environment_record() const { return false; }
     virtual bool is_function_environment_record() const { return false; }
 

Userland/Libraries/LibJS/Runtime/ObjectEnvironmentRecord.h

@@ -20,6 +20,8 @@ public:
     virtual void put_into_environment_record(FlyString const&, Variable) override;
     virtual bool delete_from_environment_record(FlyString const&) override;
 
+    Object& object() { return m_object; }
+
 private:
     virtual void visit_edges(Visitor&) override;
 

Userland/Libraries/LibJS/Runtime/VM.cpp

@@ -14,6 +14,7 @@
 #include <LibJS/Runtime/Error.h>
 #include <LibJS/Runtime/FinalizationRegistry.h>
 #include <LibJS/Runtime/FunctionEnvironmentRecord.h>
+#include <LibJS/Runtime/GlobalEnvironmentRecord.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/IteratorOperations.h>
 #include <LibJS/Runtime/NativeFunction.h>
@@ -394,14 +395,10 @@ Value VM::get_variable(const FlyString& name, GlobalObject& global_object)
 
 Reference VM::get_reference(const FlyString& name)
 {
-    if (m_call_stack.size()) {
-        for (auto* environment_record = lexical_environment(); environment_record; environment_record = environment_record->outer_environment()) {
-            if (is<GlobalObject>(environment_record))
-                break;
-            auto possible_match = environment_record->get_from_environment_record(name);
-            if (possible_match.has_value())
-                return { Reference::LocalVariable, name };
-        }
+    for (auto* environment_record = lexical_environment(); environment_record && environment_record->outer_environment(); environment_record = environment_record->outer_environment()) {
+        auto possible_match = environment_record->get_from_environment_record(name);
+        if (possible_match.has_value())
+            return { Reference::LocalVariable, name };
     }
     return { Reference::GlobalVariable, name };
 }