LibJS: Add a new EnterScope bytecode instruction

This is intended to perform the same duties as enter_scope() does in
the AST tree-walk interpreter:

- Hoisted function declaration processing
- Hoisted variable declaration processing
- ... maybe more

This first cut only implements the function declaration processing.

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -20,6 +20,7 @@ Optional<Bytecode::Register> ASTNode::generate_bytecode(Bytecode::Generator&) co
 
 Optional<Bytecode::Register> ScopeNode::generate_bytecode(Bytecode::Generator& generator) const
 {
+    generator.emit<Bytecode::Op::EnterScope>(*this);
     for (auto& child : children()) {
         [[maybe_unused]] auto reg = child.generate_bytecode(generator);
     }

Userland/Libraries/LibJS/Bytecode/Op.cpp

@@ -4,9 +4,11 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibJS/AST.h>
 #include <LibJS/Bytecode/Interpreter.h>
 #include <LibJS/Bytecode/Op.h>
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/ScriptFunction.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS::Bytecode::Op {
@@ -89,6 +91,23 @@ void JumpIfTrue::execute(Bytecode::Interpreter& interpreter) const
         interpreter.jump(m_target.value());
 }
 
+void EnterScope::execute(Bytecode::Interpreter& interpreter) const
+{
+    auto& vm = interpreter.vm();
+    auto& global_object = interpreter.global_object();
+
+    for (auto& declaration : m_scope_node.functions())
+        vm.current_scope()->put_to_scope(declaration.name(), { js_undefined(), DeclarationKind::Var });
+
+    for (auto& declaration : m_scope_node.functions()) {
+        auto* function = ScriptFunction::create(global_object, declaration.name(), declaration.body(), declaration.parameters(), declaration.function_length(), vm.current_scope(), declaration.is_strict_mode());
+        vm.set_variable(declaration.name(), function, global_object);
+    }
+
+    // FIXME: Process variable declarations.
+    // FIXME: Whatever else JS::Interpreter::enter_scope() does.
+}
+
 String Load::to_string() const
 {
     return String::formatted("Load dst:{}, value:{}", m_dst, m_value.to_string_without_side_effects());
@@ -163,4 +182,9 @@ String JumpIfTrue::to_string() const
     return String::formatted("JumpIfTrue result:{}, target:<empty>", m_result);
 }
 
+String EnterScope::to_string() const
+{
+    return "EnterScope";
+}
+
 }

Userland/Libraries/LibJS/Bytecode/Op.h

@@ -265,4 +265,19 @@ private:
     Optional<Label> m_target;
 };
 
+class EnterScope final : public Instruction {
+public:
+    explicit EnterScope(ScopeNode const& scope_node)
+        : m_scope_node(scope_node)
+    {
+    }
+
+    virtual ~EnterScope() override { }
+    virtual void execute(Bytecode::Interpreter&) const override;
+    virtual String to_string() const override;
+
+private:
+    ScopeNode const& m_scope_node;
+};
+
 }