LibJS: Implement generator functions (only in bytecode mode)

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -293,6 +293,8 @@ struct CommonPropertyNames {
     FlyString catch_ { "catch" };
     FlyString delete_ { "delete" };
     FlyString for_ { "for" };
+    FlyString return_ { "return" };
+    FlyString throw_ { "throw" };
 #define __ENUMERATE(x) FlyString x { #x };
     ENUMERATE_STANDARD_PROPERTY_NAMES(__ENUMERATE)
 #undef __ENUMERATE

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));
+}
+
+}

Userland/Libraries/LibJS/Runtime/GeneratorObject.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/Object.h>
+#include <LibJS/Runtime/ScriptFunction.h>
+
+namespace JS {
+
+class GeneratorObject final : public Object {
+    JS_OBJECT(GeneratorObject, Object);
+
+public:
+    static GeneratorObject* create(GlobalObject&, Value, ScriptFunction*, ScopeObject*, Bytecode::RegisterWindow);
+    explicit GeneratorObject(GlobalObject&);
+    virtual void initialize(GlobalObject&) override;
+    virtual ~GeneratorObject() override;
+    void visit_edges(Cell::Visitor&) override;
+
+    static GeneratorObject* typed_this(VM&, GlobalObject&);
+
+private:
+    JS_DECLARE_NATIVE_FUNCTION(next);
+    JS_DECLARE_NATIVE_FUNCTION(return_);
+    JS_DECLARE_NATIVE_FUNCTION(throw_);
+
+    Value next_impl(VM&, GlobalObject&, Optional<Value> value_to_throw);
+
+    ScopeObject* m_scope { nullptr };
+    ScriptFunction* m_generating_function { nullptr };
+    Value m_previous_value;
+    Bytecode::RegisterWindow m_frame;
+    bool m_done { false };
+};
+
+}

Userland/Libraries/LibJS/Runtime/ScriptFunction.cpp

@@ -13,7 +13,9 @@
 #include <LibJS/Interpreter.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/Error.h>
+#include <LibJS/Runtime/GeneratorObject.h>
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/NativeFunction.h>
 #include <LibJS/Runtime/ScriptFunction.h>
 #include <LibJS/Runtime/Value.h>
 
@@ -31,18 +33,19 @@ static ScriptFunction* typed_this(VM& vm, GlobalObject& global_object)
     return static_cast<ScriptFunction*>(this_object);
 }
 
-ScriptFunction* ScriptFunction::create(GlobalObject& global_object, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, bool is_strict, bool is_arrow_function)
+ScriptFunction* ScriptFunction::create(GlobalObject& global_object, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, bool is_generator, bool is_strict, bool is_arrow_function)
 {
-    return global_object.heap().allocate<ScriptFunction>(global_object, global_object, name, body, move(parameters), m_function_length, parent_scope, *global_object.function_prototype(), is_strict, is_arrow_function);
+    return global_object.heap().allocate<ScriptFunction>(global_object, global_object, name, body, move(parameters), m_function_length, parent_scope, *global_object.function_prototype(), is_generator, is_strict, is_arrow_function);
 }
 
-ScriptFunction::ScriptFunction(GlobalObject& global_object, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, Object& prototype, bool is_strict, bool is_arrow_function)
+ScriptFunction::ScriptFunction(GlobalObject& global_object, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, Object& prototype, bool is_generator, bool is_strict, bool is_arrow_function)
     : Function(prototype, is_arrow_function ? vm().this_value(global_object) : Value(), {})
     , m_name(name)
     , m_body(body)
     , m_parameters(move(parameters))
     , m_parent_scope(parent_scope)
     , m_function_length(m_function_length)
+    , m_is_generator(is_generator)
     , m_is_strict(is_strict)
     , m_is_arrow_function(is_arrow_function)
 {
@@ -152,15 +155,20 @@ Value ScriptFunction::execute_function_body()
     if (bytecode_interpreter) {
         prepare_arguments();
         if (!m_bytecode_executable.has_value()) {
-            m_bytecode_executable = Bytecode::Generator::generate(m_body);
+            m_bytecode_executable = Bytecode::Generator::generate(m_body, m_is_generator);
             if constexpr (JS_BYTECODE_DEBUG) {
                 dbgln("Compiled Bytecode::Block for function '{}':", m_name);
                 for (auto& block : m_bytecode_executable->basic_blocks)
                     block.dump(*m_bytecode_executable);
             }
         }
-        return bytecode_interpreter->run(*m_bytecode_executable);
+        auto result = bytecode_interpreter->run(*m_bytecode_executable);
+        if (!m_is_generator)
+            return result;
+
+        return GeneratorObject::create(global_object(), result, this, vm.call_frame().scope, bytecode_interpreter->snapshot_frame());
     } else {
+        VERIFY(!m_is_generator);
         OwnPtr<Interpreter> local_interpreter;
         ast_interpreter = vm.interpreter_if_exists();
 

Userland/Libraries/LibJS/Runtime/ScriptFunction.h

@@ -16,9 +16,9 @@ class ScriptFunction final : public Function {
     JS_OBJECT(ScriptFunction, Function);
 
 public:
-    static ScriptFunction* create(GlobalObject&, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, bool is_strict, bool is_arrow_function = false);
+    static ScriptFunction* create(GlobalObject&, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, bool is_generator, bool is_strict, bool is_arrow_function = false);
 
-    ScriptFunction(GlobalObject&, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, Object& prototype, bool is_strict, bool is_arrow_function = false);
+    ScriptFunction(GlobalObject&, const FlyString& name, const Statement& body, Vector<FunctionNode::Parameter> parameters, i32 m_function_length, ScopeObject* parent_scope, Object& prototype, bool is_generator, bool is_strict, bool is_arrow_function = false);
     virtual void initialize(GlobalObject&) override;
     virtual ~ScriptFunction();
 
@@ -33,6 +33,8 @@ public:
 
     void set_is_class_constructor() { m_is_class_constructor = true; };
 
+    auto& bytecode_executable() const { return m_bytecode_executable; }
+
 protected:
     virtual bool is_strict_mode() const final { return m_is_strict; }
 
@@ -51,6 +53,7 @@ private:
     Optional<Bytecode::Executable> m_bytecode_executable;
     ScopeObject* m_parent_scope { nullptr };
     i32 m_function_length { 0 };
+    bool m_is_generator { false };
     bool m_is_strict { false };
     bool m_is_arrow_function { false };
     bool m_is_class_constructor { false };