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LibJS: Add a scope object abstraction

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Both GlobalObject and LexicalEnvironment now inherit from ScopeObject,
and the VM's call frames point to a ScopeObject chain rather than just
a LexicalEnvironment chain.

This gives us much more flexibility to implement things like "with",
and also unifies some of the code paths that previously required
special handling of the global object.

There's a bunch of more cleanup that can be done in the wake of this
change, and there might be some oversights in the handling of the
"super" keyword, but this generally seems like a good architectural
improvement. :^)
This commit is contained in:
Andreas Kling 2020-11-28 16:02:27 +01:00
parent e1bbc7c075
commit c3fe9b4df8
16 changed files with 241 additions and 92 deletions
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28
Libraries/LibJS/Runtime/LexicalEnvironment.h
View file

@ -28,17 +28,14 @@
#include <AK/FlyString.h>
#include <AK/HashMap.h>
#include <LibJS/Runtime/Cell.h>
#include <LibJS/Runtime/ScopeObject.h>
#include <LibJS/Runtime/Value.h>
namespace JS {
struct Variable {
Value value;
DeclarationKind declaration_kind;
};
class LexicalEnvironment final : public ScopeObject {
JS_OBJECT(LexicalEnvironment, ScopeObject);
class LexicalEnvironment final : public Cell {
public:
enum class ThisBindingStatus {
Lexical,
@ -49,21 +46,21 @@ public:
enum class EnvironmentRecordType {
Declarative,
Function,
Global,
Object,
Module,
};
LexicalEnvironment();
LexicalEnvironment(EnvironmentRecordType);
LexicalEnvironment(HashMap<FlyString, Variable> variables, LexicalEnvironment* parent);
LexicalEnvironment(HashMap<FlyString, Variable> variables, LexicalEnvironment* parent, EnvironmentRecordType);
LexicalEnvironment(HashMap<FlyString, Variable> variables, ScopeObject* parent_scope);
LexicalEnvironment(HashMap<FlyString, Variable> variables, ScopeObject* parent_scope, EnvironmentRecordType);
virtual ~LexicalEnvironment() override;
LexicalEnvironment* parent() const { return m_parent; }
Optional<Variable> get(const FlyString&) const;
void set(GlobalObject&, const FlyString&, Variable);
// ^ScopeObject
virtual Optional<Variable> get_from_scope(const FlyString&) const override;
virtual void put_to_scope(const FlyString&, Variable) override;
virtual bool has_this_binding() const override;
virtual Value get_this_binding(GlobalObject&) const override;
void clear();
@ -73,9 +70,7 @@ public:
bool has_super_binding() const;
Value get_super_base();
bool has_this_binding() const;
ThisBindingStatus this_binding_status() const { return m_this_binding_status; }
Value get_this_binding(GlobalObject&) const;
void bind_this_value(GlobalObject&, Value this_value);
// Not a standard operation.
@ -90,12 +85,11 @@ public:
EnvironmentRecordType type() const { return m_environment_record_type; }
private:
virtual const char* class_name() const override { return "LexicalEnvironment"; }
virtual bool is_lexical_environment() const final { return true; }
virtual void visit_edges(Visitor&) override;
EnvironmentRecordType m_environment_record_type : 8 { EnvironmentRecordType::Declarative };
ThisBindingStatus m_this_binding_status : 8 { ThisBindingStatus::Uninitialized };
LexicalEnvironment* m_parent { nullptr };
HashMap<FlyString, Variable> m_variables;
Value m_home_object;
Value m_this_value;