LibJS: More properly implement scoping rules in bytecode codegen

Now we emit CreateVariable and SetVariable with the appropriate
initialization/environment modes, much closer to the spec.
This makes a whole lot of things like let/const variables, function
and variable hoisting and some other things work :^)

5 files changed, 21 insertions, 12 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp
index 214f1a28c6..17e126ffd0 100644
--- a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp
@@ -196,15 +196,21 @@ ThrowCompletionOr<bool> DeclarativeEnvironment::delete_binding(GlobalObject&, Fl
     return true;
 }
 
-void DeclarativeEnvironment::initialize_or_set_mutable_binding(Badge<ScopeNode>, GlobalObject& global_object, FlyString const& name, Value value)
+ThrowCompletionOr<void> DeclarativeEnvironment::initialize_or_set_mutable_binding(GlobalObject& global_object, FlyString const& name, Value value)
 {
     auto it = m_names.find(name);
     VERIFY(it != m_names.end());
     auto& binding = m_bindings[it->value];
     if (!binding.initialized)
-        MUST(initialize_binding(global_object, name, value));
+        TRY(initialize_binding(global_object, name, value));
     else
-        MUST(set_mutable_binding(global_object, name, value, false));
+        TRY(set_mutable_binding(global_object, name, value, false));
+    return {};
+}
+
+void DeclarativeEnvironment::initialize_or_set_mutable_binding(Badge<ScopeNode>, GlobalObject& global_object, FlyString const& name, Value value)
+{
+    MUST(initialize_or_set_mutable_binding(global_object, name, value));
 }
 
 Vector<String> DeclarativeEnvironment::bindings() const
diff --git a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h
index 934c14400d..4da324a0d8 100644
--- a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h
+++ b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h
@@ -31,6 +31,7 @@ public:
     virtual ThrowCompletionOr<bool> delete_binding(GlobalObject&, FlyString const& name) override;
 
     void initialize_or_set_mutable_binding(Badge<ScopeNode>, GlobalObject& global_object, FlyString const& name, Value value);
+    ThrowCompletionOr<void> initialize_or_set_mutable_binding(GlobalObject& global_object, FlyString const& name, Value value);
 
     // This is not a method defined in the spec! Do not use this in any LibJS (or other spec related) code.
     [[nodiscard]] Vector<String> bindings() const;
diff --git a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
index 65e29633a0..17423a6cae 100644
--- a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
@@ -542,14 +542,16 @@ ThrowCompletionOr<void> ECMAScriptFunctionObject::function_declaration_instantia
     if (!scope_body)
         return {};
 
-    scope_body->for_each_lexically_scoped_declaration([&](Declaration const& declaration) {
-        declaration.for_each_bound_name([&](auto const& name) {
-            if (declaration.is_constant_declaration())
-                MUST(lex_environment->create_immutable_binding(global_object(), name, true));
-            else
-                MUST(lex_environment->create_mutable_binding(global_object(), name, false));
+    if (!Bytecode::Interpreter::current()) {
+        scope_body->for_each_lexically_scoped_declaration([&](Declaration const& declaration) {
+            declaration.for_each_bound_name([&](auto const& name) {
+                if (declaration.is_constant_declaration())
+                    MUST(lex_environment->create_immutable_binding(global_object(), name, true));
+                else
+                    MUST(lex_environment->create_mutable_binding(global_object(), name, false));
+            });
         });
-    });
+    }
 
     auto* private_environment = callee_context.private_environment;
     for (auto& declaration : functions_to_initialize) {
diff --git a/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp b/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp
index 78d35700cd..6644e0092d 100644
--- a/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp
@@ -97,7 +97,7 @@ ThrowCompletionOr<Value> GeneratorObject::next_impl(VM& vm, GlobalObject& global
     VERIFY(!m_generating_function->bytecode_executable()->basic_blocks.find_if([next_block](auto& block) { return block == next_block; }).is_end());
 
     // Restore the snapshot registers
-    bytecode_interpreter->enter_frame(m_frame);
+    bytecode_interpreter->enter_frame(*m_frame);
 
     // Temporarily switch to the captured execution context
     TRY(vm.push_execution_context(m_execution_context, global_object));
diff --git a/Userland/Libraries/LibJS/Runtime/GeneratorObject.h b/Userland/Libraries/LibJS/Runtime/GeneratorObject.h
index 29ea61ff4d..dd84506528 100644
--- a/Userland/Libraries/LibJS/Runtime/GeneratorObject.h
+++ b/Userland/Libraries/LibJS/Runtime/GeneratorObject.h
@@ -29,7 +29,7 @@ private:
     ExecutionContext m_execution_context;
     ECMAScriptFunctionObject* m_generating_function { nullptr };
     Value m_previous_value;
-    Bytecode::RegisterWindow m_frame;
+    Optional<Bytecode::RegisterWindow> m_frame;
     bool m_done { false };
 };