LibJS: Implement generator functions (only in bytecode mode)

Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp

@@ -0,0 +1,163 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/TemporaryChange.h>
+#include <LibJS/Bytecode/Generator.h>
+#include <LibJS/Bytecode/Interpreter.h>
+#include <LibJS/Runtime/GeneratorObject.h>
+#include <LibJS/Runtime/GlobalObject.h>
+
+namespace JS {
+
+GeneratorObject* GeneratorObject::create(GlobalObject& global_object, Value initial_value, ScriptFunction* generating_function, ScopeObject* generating_scope, Bytecode::RegisterWindow frame)
+{
+    auto object = global_object.heap().allocate<GeneratorObject>(global_object, global_object);
+    object->m_generating_function = generating_function;
+    object->m_scope = generating_scope;
+    object->m_frame = move(frame);
+    object->m_previous_value = initial_value;
+    return object;
+}
+
+GeneratorObject::GeneratorObject(GlobalObject& global_object)
+    : Object(*global_object.object_prototype())
+{
+}
+
+void GeneratorObject::initialize(GlobalObject& global_object)
+{
+    auto& vm = this->vm();
+    Object::initialize(global_object);
+    define_native_function(vm.names.next, next);
+    define_native_function(vm.names.return_, return_);
+    define_native_function(vm.names.throw_, throw_);
+}
+
+GeneratorObject::~GeneratorObject()
+{
+}
+
+void GeneratorObject::visit_edges(Cell::Visitor& visitor)
+{
+    Object::visit_edges(visitor);
+    visitor.visit(m_scope);
+    visitor.visit(m_generating_function);
+    if (m_previous_value.is_object())
+        visitor.visit(&m_previous_value.as_object());
+}
+
+GeneratorObject* GeneratorObject::typed_this(VM& vm, GlobalObject& global_object)
+{
+    auto* this_object = vm.this_value(global_object).to_object(global_object);
+    if (!this_object)
+        return {};
+    if (!is<GeneratorObject>(this_object)) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::NotA, "Generator");
+        return nullptr;
+    }
+    return static_cast<GeneratorObject*>(this_object);
+}
+
+Value GeneratorObject::next_impl(VM& vm, GlobalObject& global_object, Optional<Value> value_to_throw)
+{
+    auto bytecode_interpreter = Bytecode::Interpreter::current();
+    VERIFY(bytecode_interpreter);
+
+    auto generated_value = [](Value value) {
+        if (value.is_object())
+            return value.as_object().get("result");
+        return value.is_empty() ? js_undefined() : value;
+    };
+
+    auto generated_continuation = [&](Value value) -> Bytecode::BasicBlock const* {
+        if (value.is_object())
+            return reinterpret_cast<Bytecode::BasicBlock const*>(static_cast<u64>(value.as_object().get("continuation").to_double(global_object)));
+        return nullptr;
+    };
+
+    Value previous_generated_value { generated_value(m_previous_value) };
+
+    if (vm.exception())
+        return {};
+
+    auto result = Object::create_empty(global_object);
+    result->put("value", previous_generated_value);
+
+    if (m_done) {
+        result->put("done", Value(true));
+        return result;
+    }
+
+    // Extract the continuation
+    auto next_block = generated_continuation(m_previous_value);
+    if (vm.exception())
+        return {};
+
+    if (!next_block) {
+        // The generator has terminated, now we can simply return done=true.
+        m_done = true;
+        result->put("done", Value(true));
+        return result;
+    }
+
+    // Make sure it's an actual block
+    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);
+
+    // Pretend that 'yield' returned the passed value, or threw
+    if (value_to_throw.has_value()) {
+        vm.throw_exception(global_object, value_to_throw.release_value());
+        bytecode_interpreter->accumulator() = js_undefined();
+    } else {
+        bytecode_interpreter->accumulator() = vm.argument(0);
+    }
+
+    // Temporarily switch to the captured scope
+    TemporaryChange change { vm.call_frame().scope, m_scope };
+
+    m_previous_value = bytecode_interpreter->run(*m_generating_function->bytecode_executable(), next_block);
+
+    bytecode_interpreter->leave_frame();
+
+    m_done = generated_continuation(m_previous_value) == nullptr;
+
+    result->put("value", generated_value(m_previous_value));
+    result->put("done", Value(m_done));
+
+    if (vm.exception())
+        return {};
+
+    return result;
+}
+
+JS_DEFINE_NATIVE_FUNCTION(GeneratorObject::next)
+{
+    auto object = typed_this(vm, global_object);
+    if (!object)
+        return {};
+    return object->next_impl(vm, global_object, {});
+}
+
+JS_DEFINE_NATIVE_FUNCTION(GeneratorObject::return_)
+{
+    auto object = typed_this(vm, global_object);
+    if (!object)
+        return {};
+    object->m_done = true;
+    return object->next_impl(vm, global_object, {});
+}
+
+JS_DEFINE_NATIVE_FUNCTION(GeneratorObject::throw_)
+{
+    auto object = typed_this(vm, global_object);
+    if (!object)
+        return {};
+    return object->next_impl(vm, global_object, vm.argument(0));
+}
+
+}