serenity/Userland/Libraries/LibJS/Interpreter.cpp

/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2020-2022, Linus Groh <linusg@serenityos.org>
 * Copyright (c) 2022, Luke Wilde <lukew@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/ScopeGuard.h>
#include <LibJS/AST.h>
#include <LibJS/Interpreter.h>
#include <LibJS/Runtime/AbstractOperations.h>
#include <LibJS/Runtime/ECMAScriptFunctionObject.h>
#include <LibJS/Runtime/FunctionEnvironment.h>
#include <LibJS/Runtime/GlobalEnvironment.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/Reference.h>
#include <LibJS/Runtime/Shape.h>
#include <LibJS/Runtime/Value.h>

namespace JS {

NonnullOwnPtr<Interpreter> Interpreter::create_with_existing_realm(Realm& realm)
{
    auto& vm = realm.vm();
    DeferGC defer_gc(vm.heap());
    auto interpreter = adopt_own(*new Interpreter(vm));
    interpreter->m_realm = make_handle(&realm);
    return interpreter;
}

Interpreter::Interpreter(VM& vm)
    : m_vm(vm)
{
}

// 16.1.6 ScriptEvaluation ( scriptRecord ), https://tc39.es/ecma262/#sec-runtime-semantics-scriptevaluation
ThrowCompletionOr<Value> Interpreter::run(Script& script_record, JS::GCPtr<Environment> lexical_environment_override)
{
    auto& vm = this->vm();

    VM::InterpreterExecutionScope scope(*this);

    // 1. Let globalEnv be scriptRecord.[[Realm]].[[GlobalEnv]].
    auto& global_environment = script_record.realm().global_environment();

    // 2. Let scriptContext be a new ECMAScript code execution context.
    ExecutionContext script_context(vm.heap());

    // 3. Set the Function of scriptContext to null.
    // NOTE: This was done during execution context construction.

    // 4. Set the Realm of scriptContext to scriptRecord.[[Realm]].
    script_context.realm = &script_record.realm();

    // 5. Set the ScriptOrModule of scriptContext to scriptRecord.
    script_context.script_or_module = NonnullGCPtr<Script>(script_record);

    // 6. Set the VariableEnvironment of scriptContext to globalEnv.
    script_context.variable_environment = &global_environment;

    // 7. Set the LexicalEnvironment of scriptContext to globalEnv.
    script_context.lexical_environment = &global_environment;

    // Non-standard: Override the lexical environment if requested.
    if (lexical_environment_override)
        script_context.lexical_environment = lexical_environment_override;

    // 8. Set the PrivateEnvironment of scriptContext to null.

    // NOTE: This isn't in the spec, but we require it.
    script_context.is_strict_mode = script_record.parse_node().is_strict_mode();

    // FIXME: 9. Suspend the currently running execution context.

    // 10. Push scriptContext onto the execution context stack; scriptContext is now the running execution context.
    TRY(vm.push_execution_context(script_context, {}));

    // 11. Let script be scriptRecord.[[ECMAScriptCode]].
    auto& script = script_record.parse_node();

    // 12. Let result be Completion(GlobalDeclarationInstantiation(script, globalEnv)).
    auto instantiation_result = script.global_declaration_instantiation(*this, global_environment);
    Completion result = instantiation_result.is_throw_completion() ? instantiation_result.throw_completion() : normal_completion({});

    // 13. If result.[[Type]] is normal, then
    if (result.type() == Completion::Type::Normal) {
        // a. Set result to the result of evaluating script.
        result = script.execute(*this);
    }

    // 14. If result.[[Type]] is normal and result.[[Value]] is empty, then
    if (result.type() == Completion::Type::Normal && !result.value().has_value()) {
        // a. Set result to NormalCompletion(undefined).
        result = normal_completion(js_undefined());
    }

    // FIXME: 15. Suspend scriptContext and remove it from the execution context stack.
    vm.pop_execution_context();

    // 16. Assert: The execution context stack is not empty.
    VERIFY(!vm.execution_context_stack().is_empty());

    // FIXME: 17. Resume the context that is now on the top of the execution context stack as the running execution context.

    // At this point we may have already run any queued promise jobs via on_call_stack_emptied,
    // in which case this is a no-op.
    // FIXME: These three should be moved out of Interpreter::run and give the host an option to run these, as it's up to the host when these get run.
    //        https://tc39.es/ecma262/#sec-jobs for jobs and https://tc39.es/ecma262/#_ref_3508 for ClearKeptObjects
    //        finish_execution_generation is particularly an issue for LibWeb, as the HTML spec wants to run it specifically after performing a microtask checkpoint.
    //        The promise and registry cleanup queues don't cause LibWeb an issue, as LibWeb overrides the hooks that push onto these queues.
    vm.run_queued_promise_jobs();

    vm.run_queued_finalization_registry_cleanup_jobs();

    vm.finish_execution_generation();

    // 18. Return ? result.
    if (result.is_abrupt()) {
        VERIFY(result.type() == Completion::Type::Throw);
        return result.release_error();
    }

    VERIFY(result.value().has_value());
    return *result.value();
}

ThrowCompletionOr<Value> Interpreter::run(SourceTextModule& module)
{
    // FIXME: This is not a entry point as defined in the spec, but is convenient.
    //        To avoid work we use link_and_eval_module however that can already be
    //        dangerous if the vm loaded other modules.
    auto& vm = this->vm();

    VM::InterpreterExecutionScope scope(*this);

    TRY(vm.link_and_eval_module({}, module));

    vm.run_queued_promise_jobs();

    vm.run_queued_finalization_registry_cleanup_jobs();

    return js_undefined();
}

Realm& Interpreter::realm()
{
    return static_cast<Realm&>(*m_realm.cell());
}

Realm const& Interpreter::realm() const
{
    return static_cast<Realm const&>(*m_realm.cell());
}

}