ladybird/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.cpp

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

#include <LibJS/AST.h>
#include <LibJS/Runtime/GlobalEnvironment.h>
#include <LibJS/Runtime/ModuleEnvironment.h>
#include <LibJS/Runtime/VM.h>

namespace JS {

// 9.1.2.6 NewModuleEnvironment ( E ), https://tc39.es/ecma262/#sec-newmoduleenvironment
ModuleEnvironment::ModuleEnvironment(Environment* outer_environment)
    : DeclarativeEnvironment(outer_environment)
{
}

// 9.1.1.5.1 GetBindingValue ( N, S ), https://tc39.es/ecma262/#sec-module-environment-records-getbindingvalue-n-s
ThrowCompletionOr<Value> ModuleEnvironment::get_binding_value(GlobalObject& global_object, FlyString const& name, bool strict)
{
    // 1. Assert: S is true.
    VERIFY(strict);

    // 2. Assert: envRec has a binding for N.
    auto* indirect_binding = get_indirect_binding(name);
    VERIFY(indirect_binding || !DeclarativeEnvironment::has_binding(name).is_error());

    // 3. If the binding for N is an indirect binding, then
    if (indirect_binding) {
        // a. Let M and N2 be the indirection values provided when this binding for N was created.

        // b. Let targetEnv be M.[[Environment]].
        auto* target_env = indirect_binding->module->environment();

        // c. If targetEnv is empty, throw a ReferenceError exception.
        if (!target_env)
            return vm().throw_completion<ReferenceError>(global_object, ErrorType::ModuleNoEnvironment);

        // d. Return ? targetEnv.GetBindingValue(N2, true).
        return target_env->get_binding_value(global_object, indirect_binding->binding_name, true);
    }

    // 4. If the binding for N in envRec is an uninitialized binding, throw a ReferenceError exception.
    // 5. Return the value currently bound to N in envRec.
    // Note: Step 4 & 5 are the steps performed by declarative environment GetBindingValue
    return DeclarativeEnvironment::get_binding_value(global_object, name, strict);
}

// Not defined in the spec, see comment in the header.
ThrowCompletionOr<bool> ModuleEnvironment::has_binding(FlyString const& name, Optional<size_t>* out_index) const
{
    // 1. If envRec has a binding for the name that is the value of N, return true.
    if (get_indirect_binding(name))
        return true;
    return DeclarativeEnvironment::has_binding(name, out_index);

    // 2. Return false.
}

// 9.1.1.5.2 DeleteBinding ( N ), https://tc39.es/ecma262/#sec-module-environment-records-deletebinding-n
ThrowCompletionOr<bool> ModuleEnvironment::delete_binding(GlobalObject&, FlyString const&)
{
    // The DeleteBinding concrete method of a module Environment Record is never used within this specification.
    VERIFY_NOT_REACHED();
}

// 9.1.1.5.4 GetThisBinding ( ), https://tc39.es/ecma262/#sec-module-environment-records-getthisbinding
ThrowCompletionOr<Value> ModuleEnvironment::get_this_binding(GlobalObject&) const
{
    // 1. Return undefined.
    return js_undefined();
}

// 9.1.1.5.5 CreateImportBinding ( N, M, N2 ), https://tc39.es/ecma262/#sec-createimportbinding
ThrowCompletionOr<void> ModuleEnvironment::create_import_binding(FlyString name, Module* module, FlyString binding_name)
{
    // 1. Assert: envRec does not already have a binding for N.
    VERIFY(!get_indirect_binding(name));
    // 2. Assert: When M.[[Environment]] is instantiated it will have a direct binding for N2.
    // FIXME: I don't know what this means or how to check it.

    // 3. Create an immutable indirect binding in envRec for N that references M and N2 as its target binding and record that the binding is initialized.
    // Note: We use the fact that the binding is in this list as it being initialized.
    m_indirect_bindings.append({ move(name),
        module,
        move(binding_name) });

    // 4. Return unused.
    return {};
}

ModuleEnvironment::IndirectBinding const* ModuleEnvironment::get_indirect_binding(FlyString const& name) const
{
    auto binding_or_end = m_indirect_bindings.find_if([&](IndirectBinding const& binding) {
        return binding.name == name;
    });
    if (binding_or_end.is_end())
        return nullptr;

    return &(*binding_or_end);
}

}