LibJS: Add PutById bytecode instruction for object property assignment

Note that this is only used for non-computed accesses. Computed access
is not yet implemented. :^)

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -90,6 +90,20 @@ Optional<Bytecode::Register> AssignmentExpression::generate_bytecode(Bytecode::G
         return rhs_reg;
     }
 
+    if (is<MemberExpression>(*m_lhs)) {
+        auto& expression = static_cast<MemberExpression const&>(*m_lhs);
+        auto object_reg = expression.object().generate_bytecode(generator);
+
+        if (expression.is_computed()) {
+            TODO();
+        } else {
+            VERIFY(is<Identifier>(expression.property()));
+            auto rhs_reg = m_rhs->generate_bytecode(generator);
+            generator.emit<Bytecode::Op::PutById>(*object_reg, static_cast<Identifier const&>(expression.property()).string(), *rhs_reg);
+            return rhs_reg;
+        }
+    }
+
     TODO();
 }
 

Userland/Libraries/LibJS/Bytecode/Op.cpp

@@ -56,6 +56,12 @@ void SetVariable::execute(Bytecode::Interpreter& interpreter) const
     interpreter.vm().set_variable(m_identifier, interpreter.reg(m_src), interpreter.global_object());
 }
 
+void PutById::execute(Bytecode::Interpreter& interpreter) const
+{
+    if (auto* object = interpreter.reg(m_base).to_object(interpreter.global_object()))
+        object->put(m_property, interpreter.reg(m_src));
+}
+
 void Jump::execute(Bytecode::Interpreter& interpreter) const
 {
     interpreter.jump(m_target);
@@ -122,6 +128,11 @@ String SetVariable::to_string() const
     return String::formatted("SetVariable identifier:{}, src:{}", m_identifier, m_src);
 }
 
+String PutById::to_string() const
+{
+    return String::formatted("PutById base:{}, property:{}, src:{}", m_base, m_property, m_src);
+}
+
 String Jump::to_string() const
 {
     return String::formatted("Jump {}", m_target);

Userland/Libraries/LibJS/Bytecode/Op.h

@@ -174,6 +174,25 @@ private:
     FlyString m_identifier;
 };
 
+class PutById final : public Instruction {
+public:
+    PutById(Register base, FlyString property, Register src)
+        : m_base(base)
+        , m_property(move(property))
+        , m_src(src)
+    {
+    }
+
+    virtual ~PutById() override { }
+    virtual void execute(Bytecode::Interpreter&) const override;
+    virtual String to_string() const override;
+
+private:
+    Register m_base;
+    FlyString m_property;
+    Register m_src;
+};
+
 class Jump final : public Instruction {
 public:
     explicit Jump(Label target)