ladybird/Libraries/LibJS/Interpreter.cpp

/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <AK/Badge.h>
#include <AK/StringBuilder.h>
#include <LibJS/AST.h>
#include <LibJS/Interpreter.h>
#include <LibJS/Runtime/Error.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/LexicalEnvironment.h>
#include <LibJS/Runtime/MarkedValueList.h>
#include <LibJS/Runtime/NativeFunction.h>
#include <LibJS/Runtime/Object.h>
#include <LibJS/Runtime/Reference.h>
#include <LibJS/Runtime/ScriptFunction.h>
#include <LibJS/Runtime/Shape.h>
#include <LibJS/Runtime/SymbolObject.h>
#include <LibJS/Runtime/Value.h>

//#define INTERPRETER_DEBUG

namespace JS {

Interpreter::Interpreter()
    : m_heap(*this)
    , m_console(*this)
{
}

Interpreter::~Interpreter()
{
}

Value Interpreter::run(GlobalObject& global_object, const Statement& statement, ArgumentVector arguments, ScopeType scope_type)
{
    if (statement.is_program()) {
        if (m_call_stack.is_empty()) {
            CallFrame global_call_frame;
            global_call_frame.this_value = &global_object;
            global_call_frame.function_name = "(global execution context)";
            global_call_frame.environment = heap().allocate<LexicalEnvironment>(global_object, LexicalEnvironment::EnvironmentRecordType::Global);
            global_call_frame.environment->bind_this_value(&global_object);
            if (exception())
                return {};
            m_call_stack.append(move(global_call_frame));
        }
    }

    if (!statement.is_scope_node())
        return statement.execute(*this, global_object);

    auto& block = static_cast<const ScopeNode&>(statement);
    enter_scope(block, move(arguments), scope_type, global_object);

    if (block.children().is_empty())
        m_last_value = js_undefined();

    for (auto& node : block.children()) {
        m_last_value = node.execute(*this, global_object);
        if (should_unwind()) {
            if (should_unwind_until(ScopeType::Breakable, block.label()))
                stop_unwind();
            break;
        }
    }

    bool did_return = m_unwind_until == ScopeType::Function;

    if (m_unwind_until == scope_type)
        m_unwind_until = ScopeType::None;

    exit_scope(block);

    return did_return ? m_last_value : js_undefined();
}

void Interpreter::enter_scope(const ScopeNode& scope_node, ArgumentVector arguments, ScopeType scope_type, GlobalObject& global_object)
{
    for (auto& declaration : scope_node.functions()) {
        auto* function = ScriptFunction::create(global_object, declaration.name(), declaration.body(), declaration.parameters(), declaration.function_length(), current_environment());
        set_variable(declaration.name(), function, global_object);
    }

    if (scope_type == ScopeType::Function) {
        m_scope_stack.append({ scope_type, scope_node, false });
        return;
    }

    HashMap<FlyString, Variable> scope_variables_with_declaration_kind;
    scope_variables_with_declaration_kind.ensure_capacity(16);

    for (auto& declaration : scope_node.variables()) {
        for (auto& declarator : declaration.declarations()) {
            if (scope_node.is_program()) {
                global_object.put(declarator.id().string(), js_undefined());
                if (exception())
                    return;
            } else {
                scope_variables_with_declaration_kind.set(declarator.id().string(), { js_undefined(), declaration.declaration_kind() });
            }
        }
    }

    for (auto& argument : arguments) {
        scope_variables_with_declaration_kind.set(argument.name, { argument.value, DeclarationKind::Var });
    }

    bool pushed_lexical_environment = false;

    if (!scope_variables_with_declaration_kind.is_empty()) {
        auto* block_lexical_environment = heap().allocate<LexicalEnvironment>(global_object, move(scope_variables_with_declaration_kind), current_environment());
        m_call_stack.last().environment = block_lexical_environment;
        pushed_lexical_environment = true;
    }

    m_scope_stack.append({ scope_type, scope_node, pushed_lexical_environment });
}

void Interpreter::exit_scope(const ScopeNode& scope_node)
{
    while (!m_scope_stack.is_empty()) {
        auto popped_scope = m_scope_stack.take_last();
        if (popped_scope.pushed_environment)
            m_call_stack.last().environment = m_call_stack.last().environment->parent();
        if (popped_scope.scope_node.ptr() == &scope_node)
            break;
    }

    // If we unwind all the way, just reset m_unwind_until so that future "return" doesn't break.
    if (m_scope_stack.is_empty())
        m_unwind_until = ScopeType::None;
}

void Interpreter::set_variable(const FlyString& name, Value value, GlobalObject& global_object, bool first_assignment)
{
    if (m_call_stack.size()) {
        for (auto* environment = current_environment(); environment; environment = environment->parent()) {
            auto possible_match = environment->get(name);
            if (possible_match.has_value()) {
                if (!first_assignment && possible_match.value().declaration_kind == DeclarationKind::Const) {
                    throw_exception<TypeError>(ErrorType::InvalidAssignToConst);
                    return;
                }

                environment->set(name, { value, possible_match.value().declaration_kind });
                return;
            }
        }
    }

    global_object.put(move(name), move(value));
}

Value Interpreter::get_variable(const FlyString& name, GlobalObject& global_object)
{
    if (m_call_stack.size()) {
        for (auto* environment = current_environment(); environment; environment = environment->parent()) {
            auto possible_match = environment->get(name);
            if (possible_match.has_value())
                return possible_match.value().value;
        }
    }
    auto value = global_object.get(name);
    if (m_underscore_is_last_value && name == "_" && value.is_empty())
        return m_last_value;
    return value;
}

Reference Interpreter::get_reference(const FlyString& name)
{
    if (m_call_stack.size()) {
        for (auto* environment = current_environment(); environment; environment = environment->parent()) {
            auto possible_match = environment->get(name);
            if (possible_match.has_value())
                return { Reference::LocalVariable, name };
        }
    }
    return { Reference::GlobalVariable, name };
}

void Interpreter::gather_roots(Badge<Heap>, HashTable<Cell*>& roots)
{
    roots.set(m_global_object);
    roots.set(m_exception);

    if (m_last_value.is_cell())
        roots.set(m_last_value.as_cell());

    for (auto& call_frame : m_call_stack) {
        if (call_frame.this_value.is_cell())
            roots.set(call_frame.this_value.as_cell());
        for (auto& argument : call_frame.arguments) {
            if (argument.is_cell())
                roots.set(argument.as_cell());
        }
        roots.set(call_frame.environment);
    }

    SymbolObject::gather_symbol_roots(roots);
}

Value Interpreter::call(Function& function, Value this_value, Optional<MarkedValueList> arguments)
{
    auto& call_frame = push_call_frame();
    call_frame.function_name = function.name();
    call_frame.this_value = function.bound_this().value_or(this_value);
    call_frame.arguments = function.bound_arguments();
    if (arguments.has_value())
        call_frame.arguments.append(arguments.value().values());
    call_frame.environment = function.create_environment();

    ASSERT(call_frame.environment->this_binding_status() == LexicalEnvironment::ThisBindingStatus::Uninitialized);
    call_frame.environment->bind_this_value(call_frame.this_value);

    auto result = function.call(*this);
    pop_call_frame();
    return result;
}

Value Interpreter::construct(Function& function, Function& new_target, Optional<MarkedValueList> arguments, GlobalObject& global_object)
{
    auto& call_frame = push_call_frame();
    call_frame.function_name = function.name();
    call_frame.arguments = function.bound_arguments();
    if (arguments.has_value())
        call_frame.arguments.append(arguments.value().values());
    call_frame.environment = function.create_environment();

    current_environment()->set_new_target(&new_target);

    Object* new_object = nullptr;
    if (function.constructor_kind() == Function::ConstructorKind::Base) {
        new_object = Object::create_empty(*this, global_object);
        current_environment()->bind_this_value(new_object);
        if (exception())
            return {};
        auto prototype = new_target.get("prototype");
        if (exception())
            return {};
        if (prototype.is_object()) {
            new_object->set_prototype(&prototype.as_object());
            if (exception())
                return {};
        }
    }

    // If we are a Derived constructor, |this| has not been constructed before super is called.
    Value this_value = function.constructor_kind() == Function::ConstructorKind::Base ? new_object : Value {};
    call_frame.this_value = this_value;
    auto result = function.construct(*this, new_target);

    this_value = current_environment()->get_this_binding();
    pop_call_frame();

    // If we are constructing an instance of a derived class,
    // set the prototype on objects created by constructors that return an object (i.e. NativeFunction subclasses).
    if (function.constructor_kind() == Function::ConstructorKind::Base && new_target.constructor_kind() == Function::ConstructorKind::Derived && result.is_object()) {
        current_environment()->replace_this_binding(result);
        auto prototype = new_target.get("prototype");
        if (exception())
            return {};
        if (prototype.is_object()) {
            result.as_object().set_prototype(&prototype.as_object());
            if (exception())
                return {};
        }
        return result;
    }

    if (exception())
        return {};

    if (result.is_object())
        return result;

    return this_value;
}

Value Interpreter::throw_exception(Exception* exception)
{
#ifdef INTERPRETER_DEBUG
    if (exception->value().is_object() && exception->value().as_object().is_error()) {
        auto& error = static_cast<Error&>(exception->value().as_object());
        dbg() << "Throwing JavaScript Error: " << error.name() << ", " << error.message();

        for (ssize_t i = m_call_stack.size() - 1; i >= 0; --i) {
            auto function_name = m_call_stack[i].function_name;
            if (function_name.is_empty())
                function_name = "<anonymous>";
            dbg() << "  " << function_name;
        }
    }
#endif
    m_exception = exception;
    unwind(ScopeType::Try);
    return {};
}

GlobalObject& Interpreter::global_object()
{
    return static_cast<GlobalObject&>(*m_global_object);
}

const GlobalObject& Interpreter::global_object() const
{
    return static_cast<const GlobalObject&>(*m_global_object);
}

String Interpreter::join_arguments() const
{
    StringBuilder joined_arguments;
    for (size_t i = 0; i < argument_count(); ++i) {
        joined_arguments.append(argument(i).to_string_without_side_effects().characters());
        if (i != argument_count() - 1)
            joined_arguments.append(' ');
    }
    return joined_arguments.build();
}

Value Interpreter::resolve_this_binding() const
{
    return get_this_environment()->get_this_binding();
}

const LexicalEnvironment* Interpreter::get_this_environment() const
{
    // We will always return because the Global environment will always be reached, which has a |this| binding.
    for (const LexicalEnvironment* environment = current_environment(); environment; environment = environment->parent()) {
        if (environment->has_this_binding())
            return environment;
    }
    ASSERT_NOT_REACHED();
}

Value Interpreter::get_new_target() const
{
    return get_this_environment()->new_target();
}

}