ladybird/Libraries/LibJS/SourceTextModule.cpp

/*
 * Copyright (c) 2021-2023, Andreas Kling <andreas@ladybird.org>
 * Copyright (c) 2022, David Tuin <davidot@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Debug.h>
#include <AK/QuickSort.h>
#include <LibJS/Bytecode/Executable.h>
#include <LibJS/Bytecode/Interpreter.h>
#include <LibJS/Runtime/AsyncFunctionDriverWrapper.h>
#include <LibJS/Runtime/ECMAScriptFunctionObject.h>
#include <LibJS/Runtime/GlobalEnvironment.h>
#include <LibJS/Runtime/ModuleEnvironment.h>
#include <LibJS/Runtime/PromiseCapability.h>
#include <LibJS/Runtime/SharedFunctionInstanceData.h>
#include <LibJS/RustIntegration.h>
#include <LibJS/Script.h>
#include <LibJS/SourceCode.h>
#include <LibJS/SourceTextModule.h>

namespace JS {

GC_DEFINE_ALLOCATOR(SourceTextModule);

SourceTextModule::SourceTextModule(Realm& realm, StringView filename, Script::HostDefined* host_defined, bool has_top_level_await,
    Vector<ModuleRequest> requested_modules, Vector<ImportEntry> import_entries,
    Vector<ExportEntry> local_export_entries, Vector<ExportEntry> indirect_export_entries,
    Vector<ExportEntry> star_export_entries, Optional<Utf16FlyString> default_export_binding_name,
    Vector<Utf16FlyString> var_declared_names, Vector<LexicalBinding> lexical_bindings,
    Vector<FunctionToInitialize> functions_to_initialize,
    GC::Ptr<Bytecode::Executable> executable,
    GC::Ptr<SharedFunctionInstanceData> tla_shared_data)
    : CyclicModule(realm, filename, has_top_level_await, move(requested_modules), host_defined)
    , m_execution_context(ExecutionContext::create(0, ReadonlySpan<Value> {}, 0))
    , m_import_entries(move(import_entries))
    , m_local_export_entries(move(local_export_entries))
    , m_indirect_export_entries(move(indirect_export_entries))
    , m_star_export_entries(move(star_export_entries))
    , m_var_declared_names(move(var_declared_names))
    , m_lexical_bindings(move(lexical_bindings))
    , m_functions_to_initialize(move(functions_to_initialize))
    , m_default_export_binding_name(move(default_export_binding_name))
    , m_executable(executable)
    , m_tla_shared_data(tla_shared_data)
{
}

SourceTextModule::~SourceTextModule() = default;

void SourceTextModule::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    visitor.visit(m_import_meta);
    m_execution_context->visit_edges(visitor);
    for (auto const& function : m_functions_to_initialize)
        visitor.visit(function.shared_data);
    visitor.visit(m_executable);
    visitor.visit(m_tla_shared_data);
}

Result<GC::Ref<SourceTextModule>, Vector<ParserError>> SourceTextModule::parse_from_pre_parsed(FFI::ParsedProgram* parsed, NonnullRefPtr<SourceCode const> source_code, Realm& realm, Script::HostDefined* host_defined)
{
    auto filename = source_code->filename();
    auto rust_result = RustIntegration::compile_parsed_module(parsed, move(source_code), realm);
    // Always from the Rust pipeline, so the Optional must have a value.
    VERIFY(rust_result.has_value());
    if (rust_result->is_error())
        return rust_result->release_error();
    auto& module_result = rust_result->value();
    Vector<FunctionToInitialize> functions_to_initialize;
    functions_to_initialize.ensure_capacity(module_result.functions_to_initialize.size());
    for (auto& f : module_result.functions_to_initialize)
        functions_to_initialize.append({ *f.shared_data, move(f.name) });
    return realm.heap().allocate<SourceTextModule>(
        realm, filename, host_defined, module_result.has_top_level_await,
        move(module_result.requested_modules), move(module_result.import_entries),
        move(module_result.local_export_entries), move(module_result.indirect_export_entries),
        move(module_result.star_export_entries), move(module_result.default_export_binding_name),
        move(module_result.var_declared_names), move(module_result.lexical_bindings),
        move(functions_to_initialize),
        module_result.executable.ptr(), module_result.tla_shared_data.ptr());
}

// 16.2.1.7.1 ParseModule ( sourceText, realm, hostDefined ), https://tc39.es/ecma262/#sec-parsemodule
Result<GC::Ref<SourceTextModule>, Vector<ParserError>> SourceTextModule::parse(StringView source_text, Realm& realm, StringView filename, Script::HostDefined* host_defined)
{
    auto rust_result = RustIntegration::compile_module(source_text, realm, filename);
    if (!rust_result.has_value())
        return Vector<ParserError> {};
    if (rust_result->is_error())
        return rust_result->release_error();

    auto& module_result = rust_result->value();
    Vector<FunctionToInitialize> functions_to_initialize;
    functions_to_initialize.ensure_capacity(module_result.functions_to_initialize.size());
    for (auto& f : module_result.functions_to_initialize)
        functions_to_initialize.append({ *f.shared_data, move(f.name) });
    return realm.heap().allocate<SourceTextModule>(
        realm, filename, host_defined, module_result.has_top_level_await,
        move(module_result.requested_modules), move(module_result.import_entries),
        move(module_result.local_export_entries), move(module_result.indirect_export_entries),
        move(module_result.star_export_entries), move(module_result.default_export_binding_name),
        move(module_result.var_declared_names), move(module_result.lexical_bindings),
        move(functions_to_initialize),
        module_result.executable.ptr(), module_result.tla_shared_data.ptr());
}

// 16.2.1.7.2.1 GetExportedNames ( [ exportStarSet ] ), https://tc39.es/ecma262/#sec-getexportednames
Vector<Utf16FlyString> SourceTextModule::get_exported_names(VM& vm, HashTable<Module const*>& export_star_set)
{
    dbgln_if(JS_MODULE_DEBUG, "[JS MODULE] get_export_names of {}", filename());

    // 1. Assert: module.[[Status]] is not NEW.
    VERIFY(m_status != ModuleStatus::New);

    // 2. If exportStarSet is not present, set exportStarSet to a new empty List.
    // NOTE: This is done by Module.

    // 3. If exportStarSet contains module, then
    if (export_star_set.contains(this)) {
        // a. Assert: We've reached the starting point of an export * circularity.
        // FIXME: How do we check that?

        // b. Return a new empty List.
        return {};
    }

    // 4. Append module to exportStarSet.
    export_star_set.set(this);

    // 5. Let exportedNames be a new empty List.
    Vector<Utf16FlyString> exported_names;

    // 6. For each ExportEntry Record e of module.[[LocalExportEntries]], do
    for (auto const& entry : m_local_export_entries) {
        // a. Assert: module provides the direct binding for this export.
        // FIXME: How do we check that?

        // b. Assert: e.[[ExportName]] is not null.
        VERIFY(entry.export_name.has_value());

        // c. Append e.[[ExportName]] to exportedNames.
        exported_names.empend(entry.export_name.value());
    }

    // 7. For each ExportEntry Record e of module.[[IndirectExportEntries]], do
    for (auto const& entry : m_indirect_export_entries) {
        // a. a. Assert: module imports a specific binding for this export.
        // FIXME: How do we check that?

        // b. Assert: e.[[ExportName]] is not null.
        VERIFY(entry.export_name.has_value());

        // c. Append e.[[ExportName]] to exportedNames.
        exported_names.empend(entry.export_name.value());
    }

    // 8. For each ExportEntry Record e of module.[[StarExportEntries]], do
    for (auto const& entry : m_star_export_entries) {
        // a. Assert: e.[[ModuleRequest]] is not null.
        // b. Let requestedModule be GetImportedModule(module, e.[[ModuleRequest]]).
        auto requested_module = get_imported_module(entry.module_request());

        // c. Let starNames be requestedModule.GetExportedNames(exportStarSet).
        auto star_names = requested_module->get_exported_names(vm, export_star_set);

        // d. For each element n of starNames, do
        for (auto const& name : star_names) {
            // i. If n is not "default", then
            if (name != "default"sv) {
                // 1. If exportedNames does not contain n, then
                if (!exported_names.contains_slow(name)) {
                    // a. Append n to exportedNames.
                    exported_names.empend(name);
                }
            }
        }
    }

    // 9. Return exportedNames.
    return exported_names;
}

// 16.2.1.7.3.1 InitializeEnvironment ( ), https://tc39.es/ecma262/#sec-source-text-module-record-initialize-environment
ThrowCompletionOr<void> SourceTextModule::initialize_environment(VM& vm)
{
    // 1. For each ExportEntry Record e of module.[[IndirectExportEntries]], do
    for (auto const& entry : m_indirect_export_entries) {
        // a. Assert: e.[[ExportName]] is not null.
        VERIFY(entry.export_name.has_value());

        // a. Let resolution be module.ResolveExport(e.[[ExportName]]).
        auto resolution = resolve_export(vm, entry.export_name.value());

        // b. If resolution is either null or AMBIGUOUS, throw a SyntaxError exception.
        if (!resolution.is_valid())
            return vm.throw_completion<SyntaxError>(ErrorType::InvalidOrAmbiguousExportEntry, entry.export_name);

        // c. Assert: resolution is a ResolvedBinding Record.
        VERIFY(resolution.is_valid());
    }

    // 2. Assert: All named exports from module are resolvable.
    // NOTE: We check all the indirect export entries above in step 1 and all the local named exports are resolvable by construction.

    // 3. Let realm be module.[[Realm]].
    // 4. Assert: realm is not undefined.
    auto& realm = this->realm();

    // 5. Let env be NewModuleEnvironment(realm.[[GlobalEnv]]).
    auto environment = vm.heap().allocate<ModuleEnvironment>(&realm.global_environment());

    // 6. Set module.[[Environment]] to env.
    set_environment(environment);

    // 7. For each ImportEntry Record in of module.[[ImportEntries]], do
    for (auto const& import_entry : m_import_entries) {
        // a. Let importedModule be GetImportedModule(module, in.[[ModuleRequest]]).
        auto imported_module = get_imported_module(import_entry.module_request());

        // b. If in.[[ImportName]] is NAMESPACE-OBJECT, then
        if (import_entry.is_namespace()) {
            // i. Let namespace be GetModuleNamespace(importedModule).
            auto namespace_ = imported_module->get_module_namespace(vm);

            // ii. Perform ! env.CreateImmutableBinding(in.[[LocalName]], true).
            MUST(environment->create_immutable_binding(vm, import_entry.local_name, true));

            // iii. Perform ! env.InitializeBinding(in.[[LocalName]], namespace, normal).
            MUST(environment->initialize_binding(vm, import_entry.local_name, namespace_, Environment::InitializeBindingHint::Normal));
        }
        // c. Else,
        else {
            auto const& import_name = import_entry.import_name.value();

            // i. Let resolution be importedModule.ResolveExport(in.[[ImportName]]).
            auto resolution = imported_module->resolve_export(vm, import_name);

            // ii. If resolution is either null or AMBIGUOUS, throw a SyntaxError exception.
            if (!resolution.is_valid())
                return vm.throw_completion<SyntaxError>(ErrorType::InvalidOrAmbiguousExportEntry, import_name);

            // iii. If resolution.[[BindingName]] is NAMESPACE, then
            if (resolution.is_namespace()) {
                // 1. Let namespace be GetModuleNamespace(resolution.[[Module]]).
                auto namespace_ = resolution.module->get_module_namespace(vm);

                // 2. Perform ! env.CreateImmutableBinding(in.[[LocalName]], true).
                MUST(environment->create_immutable_binding(vm, import_entry.local_name, true));

                // 3. Perform ! env.InitializeBinding(in.[[LocalName]], namespace, normal).
                MUST(environment->initialize_binding(vm, import_entry.local_name, namespace_, Environment::InitializeBindingHint::Normal));
            }
            // iv. Else,
            else {
                // 1. Perform env.CreateImportBinding(in.[[LocalName]], resolution.[[Module]], resolution.[[BindingName]]).
                MUST(environment->create_import_binding(import_entry.local_name, resolution.module, resolution.export_name));
            }
        }
    }

    // 8. Let moduleContext be a new ECMAScript code execution context.
    // NOTE: this has already been created during the construction of this object.

    // 9. Set the Function of moduleContext to null.

    // 10. Assert: module.[[Realm]] is not undefined.
    // NOTE: This must be true because we use a reference.

    // 11. Set the Realm of moduleContext to module.[[Realm]].
    m_execution_context->realm = &this->realm();

    // 12. Set the ScriptOrModule of moduleContext to module.
    m_execution_context->script_or_module = GC::Ref<Module>(*this);

    // 13. Set the VariableEnvironment of moduleContext to module.[[Environment]].
    m_execution_context->variable_environment = environment;

    // 14. Set the LexicalEnvironment of moduleContext to module.[[Environment]].
    m_execution_context->lexical_environment = environment;

    // 15. Set the PrivateEnvironment of moduleContext to null.

    // 16. Set module.[[Context]] to moduleContext.
    // NOTE: We're already working on that one.

    // 17. Push moduleContext onto the execution context stack; moduleContext is now the running execution context.
    TRY(vm.push_execution_context(*m_execution_context, {}));

    // 18. Let code be module.[[ECMAScriptCode]].

    // 19. Let varDeclarations be the VarScopedDeclarations of code.
    // 20. Let declaredVarNames be a new empty List.
    Vector<Utf16FlyString> declared_var_names;

    // 21. For each element d of varDeclarations, do
    // a. For each element dn of the BoundNames of d, do
    for (auto const& name : m_var_declared_names) {
        // i. If dn is not an element of declaredVarNames, then
        if (!declared_var_names.contains_slow(name)) {
            // 1. Perform ! env.CreateMutableBinding(dn, false).
            MUST(environment->create_mutable_binding(vm, name, false));

            // 2. Perform ! env.InitializeBinding(dn, undefined, normal).
            MUST(environment->initialize_binding(vm, name, js_undefined(), Environment::InitializeBindingHint::Normal));

            // 3. Append dn to declaredVarNames.
            declared_var_names.empend(name);
        }
    }

    // 22. Let lexDeclarations be the LexicallyScopedDeclarations of code.
    // 23. Let privateEnv be null.
    PrivateEnvironment* private_environment = nullptr;

    // 24. For each element d of lexDeclarations, do
    for (auto const& binding : m_lexical_bindings) {
        // a. For each element dn of the BoundNames of d, do
        // i. If IsConstantDeclaration of d is true, then
        if (binding.is_constant) {
            // 1. Perform ! env.CreateImmutableBinding(dn, true).
            MUST(environment->create_immutable_binding(vm, binding.name, true));
        }
        // ii. Else,
        else {
            // 1. Perform ! env.CreateMutableBinding(dn, false).
            MUST(environment->create_mutable_binding(vm, binding.name, false));
        }

        // iii. If d is a FunctionDeclaration, a GeneratorDeclaration, an AsyncFunctionDeclaration, or an AsyncGeneratorDeclaration, then
        if (binding.function_index >= 0) {
            auto const& function_to_initialize = m_functions_to_initialize[binding.function_index];

            // 1. Let fo be InstantiateFunctionObject of d with arguments env and privateEnv.
            auto function = ECMAScriptFunctionObject::create_from_function_data(
                realm,
                function_to_initialize.shared_data,
                environment,
                private_environment);

            // 2. Perform ! env.InitializeBinding(dn, fo, normal).
            MUST(environment->initialize_binding(vm, binding.name, function, Environment::InitializeBindingHint::Normal));
        }
    }

    // NOTE: The default export name is also part of the local lexical declarations but instead of making that a special
    //       case in the parser we just check it here. This is only needed for things which are not declarations. For more
    //       info check Parser::parse_export_statement. Furthermore, that declaration is not constant. so we take 24.a.ii.
    if (m_default_export_binding_name.has_value())
        MUST(environment->create_mutable_binding(vm, *m_default_export_binding_name, false));

    // 25. Remove moduleContext from the execution context stack.
    vm.pop_execution_context();

    // 26. Return unused.
    return {};
}

// 16.2.1.7.2.2 ResolveExport ( exportName [ , resolveSet ] ), https://tc39.es/ecma262/#sec-resolveexport
ResolvedBinding SourceTextModule::resolve_export(VM& vm, Utf16FlyString const& export_name, Vector<ResolvedBinding> resolve_set)
{
    // 1. Assert: module.[[Status]] is not NEW.
    VERIFY(m_status != ModuleStatus::New);

    // 2. If resolveSet is not present, set resolveSet to a new empty List.
    // NOTE: This is done by the default argument.

    // 3. For each Record { [[Module]], [[ExportName]] } r of resolveSet, do
    for (auto const& [type, module, exported_name] : resolve_set) {
        // a. If module and r.[[Module]] are the same Module Record and exportName is r.[[ExportName]], then
        if (module == this && exported_name == export_name) {
            // i. Assert: This is a circular import request.

            // ii. Return null.
            return ResolvedBinding::null();
        }
    }

    // 4. Append the Record { [[Module]]: module, [[ExportName]]: exportName } to resolveSet.
    resolve_set.append({ ResolvedBinding::Type::BindingName, this, export_name });

    // 5. For each ExportEntry Record e of module.[[LocalExportEntries]], do
    for (auto const& entry : m_local_export_entries) {
        // a. If e.[[ExportName]] is exportName, then
        if (export_name != entry.export_name)
            continue;

        // i. Assert: module provides the direct binding for this export.
        // FIXME: What does this mean?

        // ii. Return ResolvedBinding Record { [[Module]]: module, [[BindingName]]: e.[[LocalName]] }.
        return ResolvedBinding {
            ResolvedBinding::Type::BindingName,
            this,
            entry.local_or_import_name.value(),
        };
    }

    // 5. For each ExportEntry Record e of module.[[IndirectExportEntries]], do
    for (auto const& entry : m_indirect_export_entries) {
        // a. If e.[[ExportName]] is exportName, then
        if (export_name != entry.export_name)
            continue;

        // i. Assert: e.[[ModuleRequest]] is not null.
        // ii. Let importedModule be GetImportedModule(module, e.[[ModuleRequest]]).
        auto imported_module = get_imported_module(entry.module_request());

        // iii. If e.[[ImportName]] is all, then
        if (entry.kind == ExportEntry::Kind::ModuleRequestAll) {
            // 1. Assert: module does not provide the direct binding for this export.
            // FIXME: What does this mean? / How do we check this

            // 2. Return ResolvedBinding Record { [[Module]]: importedModule, [[BindingName]]: NAMESPACE }.
            return ResolvedBinding {
                ResolvedBinding::Type::Namespace,
                imported_module.ptr(),
                {}
            };
        }
        // iv. Else,
        else {
            // 1. Assert: module imports a specific binding for this export.
            // FIXME: What does this mean? / How do we check this

            // 2. Return importedModule.ResolveExport(e.[[ImportName]], resolveSet).
            return imported_module->resolve_export(vm, entry.local_or_import_name.value(), resolve_set);
        }
    }

    // 7. If exportName is "default", then
    if (export_name == "default"sv) {
        // a. Assert: A default export was not explicitly defined by this module.
        // FIXME: What does this mean? / How do we check this

        // b. Return null.
        return ResolvedBinding::null();

        // c. NOTE: A default export cannot be provided by an export * from "mod" declaration.
    }

    // 8. Let starResolution be null.
    auto star_resolution = ResolvedBinding::null();

    // 9. For each ExportEntry Record e of module.[[StarExportEntries]], do
    for (auto const& entry : m_star_export_entries) {
        // a. Assert: e.[[ModuleRequest]] is not null.
        // b. Let importedModule be GetImportedModule(module, e.[[ModuleRequest]]).
        auto imported_module = get_imported_module(entry.module_request());

        // c. Let resolution be importedModule.ResolveExport(exportName, resolveSet).
        auto resolution = imported_module->resolve_export(vm, export_name, resolve_set);

        // d. If resolution is AMBIGUOUS, return AMBIGUOUS.
        if (resolution.is_ambiguous())
            return ResolvedBinding::ambiguous();

        // e. If resolution is not null, then
        if (resolution.type == ResolvedBinding::Null)
            continue;

        // i. Assert: resolution is a ResolvedBinding Record.
        VERIFY(resolution.is_valid());

        // ii. If starResolution is null, set starResolution to resolution.
        if (star_resolution.type == ResolvedBinding::Null) {
            star_resolution = resolution;
        }
        // iii. Else,
        else {
            // 1. Assert: There is more than one * export that includes the requested name.
            // FIXME: Assert this

            // 2. If resolution.[[Module]] and starResolution.[[Module]] are not the same Module Record, return AMBIGUOUS.
            if (resolution.module != star_resolution.module)
                return ResolvedBinding::ambiguous();

            // 3. If resolution.[[BindingName]] is not starResolution.[[BindingName]] and either resolution.[[BindingName]]
            //    or starResolution.[[BindingName]] is NAMESPACE, return AMBIGUOUS.
            if (resolution.is_namespace() != star_resolution.is_namespace())
                return ResolvedBinding::ambiguous();

            // 4. If resolution.[[BindingName]] is a String, starResolution.[[BindingName]] is a String, and
            //    resolution.[[BindingName]] is not starResolution.[[BindingName]], return ambiguous.
            // NOTE: We know from the previous step that either both are namespaces or both are string, so we can check just one.
            if (!resolution.is_namespace() && resolution.export_name != star_resolution.export_name)
                return ResolvedBinding::ambiguous();
        }
    }

    // 10. Return starResolution.
    return star_resolution;
}

// 16.2.1.6.5 ExecuteModule ( [ capability ] ), https://tc39.es/ecma262/#sec-source-text-module-record-execute-module
// 9.1.1.1.2 ExecuteModule ( [ capability ] ), https://tc39.es/proposal-explicit-resource-management/#sec-source-text-module-record-execute-module
ThrowCompletionOr<void> SourceTextModule::execute_module(VM& vm, GC::Ptr<PromiseCapability> capability)
{
    dbgln_if(JS_MODULE_DEBUG, "[JS MODULE] SourceTextModule::execute_module({}, PromiseCapability @ {})", filename(), capability.ptr());

    VERIFY(m_has_top_level_await || m_executable);

    u32 registers_and_locals_count = 0;
    ReadonlySpan<Value> constants;
    if (m_executable) {
        registers_and_locals_count = m_executable->registers_and_locals_count;
        constants = m_executable->constants;
    }

    // 1. Let moduleContext be a new ECMAScript code execution context.
    auto& stack = vm.interpreter_stack();
    auto* stack_mark = stack.top();
    auto* module_context = stack.allocate(registers_and_locals_count, constants, 0);
    if (!module_context) [[unlikely]]
        return vm.throw_completion<InternalError>(ErrorType::CallStackSizeExceeded);
    ScopeGuard deallocate_guard = [&stack, stack_mark] { stack.deallocate(stack_mark); };

    // 2. Set the Function of moduleContext to null.

    // 3. Set the Realm of moduleContext to module.[[Realm]].
    module_context->realm = &realm();

    // 4. Set the ScriptOrModule of moduleContext to module.
    module_context->script_or_module = GC::Ref<Module>(*this);

    // 5. Assert: module has been linked and declarations in its module environment have been instantiated.
    VERIFY(m_status != ModuleStatus::New);
    VERIFY(m_status != ModuleStatus::Unlinked);
    VERIFY(m_status != ModuleStatus::Linking);
    VERIFY(environment());

    // 6. Set the VariableEnvironment of moduleContext to module.[[Environment]].
    module_context->variable_environment = environment();

    // 7. Set the LexicalEnvironment of moduleContext to module.[[Environment]].
    module_context->lexical_environment = environment();

    // 8. Suspend the currently running execution context.
    // NOTE: Done by the push of execution context in steps below.

    // 9. If module.[[HasTLA]] is false, then
    if (!m_has_top_level_await) {
        // a. Assert: capability is not present.
        VERIFY(capability == nullptr);

        // b. Push moduleContext onto the execution context stack; moduleContext is now the running execution context.
        TRY(vm.push_execution_context(*module_context, {}));

        // c. Let result be the result of evaluating module.[[ECMAScriptCode]].
        Completion result;

        auto result_or_error = vm.bytecode_interpreter().run_executable(*module_context, *m_executable, {});
        if (result_or_error.is_error()) {
            result = result_or_error.release_error();
        } else {
            result = result_or_error.value().is_special_empty_value() ? js_undefined() : result_or_error.release_value();
        }

        // d. Let env be moduleContext's LexicalEnvironment.
        auto& env = as<DeclarativeEnvironment>(*module_context->lexical_environment);

        // e. Set result to Completion(DisposeResources(env.[[DisposeCapability]], result)).
        result = dispose_resources(vm, env.dispose_capability(), result);

        // f. Suspend moduleContext and remove it from the execution context stack.
        vm.pop_execution_context();

        // g. Resume the context that is now on the top of the execution context stack as the running execution context.
        // FIXME: We don't have resume yet.

        // h. If result is an abrupt completion, then
        if (result.is_error()) {
            // i. Return ? result.
            return result.release_error();
        }
    }
    // 10. Else,
    else {
        // a. Assert: capability is a PromiseCapability Record.
        VERIFY(capability != nullptr);

        // b. Perform AsyncBlockStart(capability, module.[[ECMAScriptCode]], moduleContext).

        // AD-HOC: We implement asynchronous execution via synthetic generator functions,
        //         so we fake "AsyncBlockStart" here by creating an async function to wrap
        //         the top-level module code.
        // FIXME: Improve this situation, so we can match the spec better.

        // NOTE: Like AsyncBlockStart, we need to push/pop the moduleContext around the function construction to ensure that
        //       the async execution context captures the module execution context.
        vm.push_execution_context(*module_context);

        auto module_wrapper_function = ECMAScriptFunctionObject::create_from_function_data(
            realm(), *m_tla_shared_data, environment(), nullptr);

        vm.pop_execution_context();

        auto result = call(vm, Value { module_wrapper_function }, js_undefined(), ReadonlySpan<Value> {});

        // AD-HOC: This is basically analogous to what AsyncBlockStart would do.
        if (result.is_throw_completion()) {
            MUST(call(vm, *capability->reject(), js_undefined(), result.throw_completion().value()));
        } else {
            MUST(call(vm, *capability->resolve(), js_undefined(), result.value()));
        }
    }

    // 11. Return unused.
    return {};
}

}