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//! Generator built-in methods
use crate::prelude::{Box, Rc, RefCell};
use crate::error::JsError;
use crate::gc::{Gc, Guard};
use crate::interpreter::Interpreter;
use crate::value::{
BytecodeGeneratorState, CheapClone, ExoticObject, GeneratorStatus, Guarded, JsObject, JsString,
JsSymbol, JsValue, PropertyKey,
};
/// Initialize Generator.prototype
pub fn init_generator_prototype(interp: &mut Interpreter) {
let proto = interp.generator_prototype.clone();
// Set Symbol.toStringTag
let tag_key = PropertyKey::String(interp.intern("@@toStringTag"));
proto
.borrow_mut()
.set_property(tag_key, JsValue::String(JsString::from("Generator")));
interp.register_method(&proto, "next", generator_next, 1);
interp.register_method(&proto, "return", generator_return, 1);
interp.register_method(&proto, "throw", generator_throw, 1);
let well_known = interp.well_known_symbols;
// Add Symbol.iterator - returns the generator itself
// This makes generators work with for-of loops
let sym_iterator = interp.intern("Symbol.iterator");
let iterator_symbol = JsSymbol::new(well_known.iterator, Some(sym_iterator));
let iterator_key = PropertyKey::Symbol(Box::new(iterator_symbol));
// Create the [Symbol.iterator]() method that returns `this`
let iterator_fn = interp.create_native_function("[Symbol.iterator]", generator_iterator, 0);
proto
.borrow_mut()
.set_property(iterator_key, JsValue::Object(iterator_fn));
// Add Symbol.asyncIterator - returns the generator itself
// This makes async generators work with for-await-of
let sym_async_iterator = interp.intern("Symbol.asyncIterator");
let async_iterator_symbol = JsSymbol::new(well_known.async_iterator, Some(sym_async_iterator));
let async_iterator_key = PropertyKey::Symbol(Box::new(async_iterator_symbol));
// Create the [Symbol.asyncIterator]() method that returns `this`
let async_iterator_fn =
interp.create_native_function("[Symbol.asyncIterator]", generator_async_iterator, 0);
proto
.borrow_mut()
.set_property(async_iterator_key, JsValue::Object(async_iterator_fn));
}
/// Generator.prototype[Symbol.iterator]() - returns the generator itself
fn generator_iterator(
_interp: &mut Interpreter,
this: JsValue,
_args: &[JsValue],
) -> Result<Guarded, JsError> {
// Simply return `this` - the generator is its own iterator
Ok(Guarded::unguarded(this))
}
/// Generator.prototype[Symbol.asyncIterator]() - returns the generator itself
fn generator_async_iterator(
_interp: &mut Interpreter,
this: JsValue,
_args: &[JsValue],
) -> Result<Guarded, JsError> {
// Simply return `this` - the generator is its own async iterator
Ok(Guarded::unguarded(this))
}
/// Create a generator result object { value, done }
pub fn create_generator_result(interp: &mut Interpreter, value: JsValue, done: bool) -> Guarded {
let value_key = PropertyKey::String(interp.intern("value"));
let done_key = PropertyKey::String(interp.intern("done"));
let guard = interp.heap.create_guard();
// Guard the value if it's an object to prevent GC
if let JsValue::Object(ref val_obj) = value {
guard.guard(val_obj.clone());
}
let obj = interp.create_object(&guard);
{
let mut o = obj.borrow_mut();
o.set_property(value_key, value);
o.set_property(done_key, JsValue::Boolean(done));
}
Guarded::with_guard(JsValue::Object(obj), guard)
}
/// Generator.prototype.next(value)
pub fn generator_next(
interp: &mut Interpreter,
this: JsValue,
args: &[JsValue],
) -> Result<Guarded, JsError> {
let JsValue::Object(obj) = this else {
return Err(JsError::type_error(
"Generator.prototype.next called on non-object",
));
};
// Get the bytecode generator state
let obj_ref = obj.borrow();
match &obj_ref.exotic {
ExoticObject::BytecodeGenerator(state) => {
let gen_state = state.clone();
let is_async = gen_state.borrow().is_async;
drop(obj_ref); // Release borrow before calling resume_bytecode_generator
// Check if generator is already completed
{
let state = gen_state.borrow();
if state.status == GeneratorStatus::Completed {
let result = create_generator_result(interp, JsValue::Undefined, true);
return if is_async {
wrap_in_fulfilled_promise(interp, result)
} else {
Ok(result)
};
}
}
// Check if we're delegating to another iterator (yield*)
let delegated = {
let state = gen_state.borrow();
state.delegated_iterator.clone()
};
if let Some((iter_obj, next_method)) = delegated {
// Guard the iterator object during the call to prevent GC collection
let iter_guard = interp.heap.create_guard();
iter_guard.guard(iter_obj.cheap_clone());
// Forward next() to the delegated iterator
let sent_value = args.first().cloned().unwrap_or(JsValue::Undefined);
let result = interp.call_function(
next_method.clone(),
JsValue::Object(iter_obj.cheap_clone()),
&[sent_value],
)?;
// Keep guard alive until after call_function returns
let _ = iter_guard;
// For async generators, the delegated iterator might also be async.
// In that case, result.value is a Promise. We need to check for this
// and return a Promise that resolves to the proper iterator result.
if is_async {
if let JsValue::Object(result_obj) = &result.value {
if matches!(result_obj.borrow().exotic, ExoticObject::Promise(_)) {
// The delegated iterator returned a Promise.
// We need to wrap this in handling that:
// 1. Awaits the promise
// 2. Checks if done
// 3. Either yields the value or resumes the outer generator
//
// For now, we return a Promise that resolves to the inner result
// and handle the done/value logic in continuation.
// This is complex, so we use a simpler approach:
// Store that we need to await and handle on next .next() call
//
// Actually, the cleanest fix is to return the inner promise
// wrapped with .then() to handle the done check.
// But that requires promise chaining infrastructure.
//
// Simplest fix: await the promise now using resolve_promise_sync
let promise_result =
super::promise::resolve_promise_sync(interp, result_obj)?;
let (value, done) = interp.extract_iterator_result(&promise_result);
if done {
// Clear delegation and resume outer generator with the return value
gen_state.borrow_mut().delegated_iterator = None;
gen_state.borrow_mut().sent_value = value;
let result = interp.resume_bytecode_generator(&gen_state)?;
wrap_in_fulfilled_promise(interp, result)
} else {
// Yield the delegated value
let result = create_generator_result(interp, value, false);
wrap_in_fulfilled_promise(interp, result)
}
} else {
// Result is not a Promise, extract value/done directly
let (value, done) = interp.extract_iterator_result(&result.value);
if done {
gen_state.borrow_mut().delegated_iterator = None;
gen_state.borrow_mut().sent_value = value;
let result = interp.resume_bytecode_generator(&gen_state)?;
wrap_in_fulfilled_promise(interp, result)
} else {
let result = create_generator_result(interp, value, false);
wrap_in_fulfilled_promise(interp, result)
}
}
} else {
// Result is not an object, treat as done
gen_state.borrow_mut().delegated_iterator = None;
gen_state.borrow_mut().sent_value = JsValue::Undefined;
let result = interp.resume_bytecode_generator(&gen_state)?;
wrap_in_fulfilled_promise(interp, result)
}
} else {
// Sync generator - extract value/done directly
let (value, done) = interp.extract_iterator_result(&result.value);
if done {
// Clear delegation and resume outer generator with the return value
gen_state.borrow_mut().delegated_iterator = None;
gen_state.borrow_mut().sent_value = value;
interp.resume_bytecode_generator(&gen_state)
} else {
// Yield the delegated value
Ok(create_generator_result(interp, value, false))
}
}
} else {
// Set the sent value
{
let mut state = gen_state.borrow_mut();
state.sent_value = args.first().cloned().unwrap_or(JsValue::Undefined);
}
// Resume the bytecode generator
let result = interp.resume_bytecode_generator(&gen_state)?;
if is_async {
wrap_in_fulfilled_promise(interp, result)
} else {
Ok(result)
}
}
}
_ => Err(JsError::type_error(
"Generator.prototype.next called on non-generator",
)),
}
}
/// Generator.prototype.return(value)
pub fn generator_return(
interp: &mut Interpreter,
this: JsValue,
args: &[JsValue],
) -> Result<Guarded, JsError> {
let JsValue::Object(obj) = this else {
return Err(JsError::type_error(
"Generator.prototype.return called on non-object",
));
};
let value = args.first().cloned().unwrap_or(JsValue::Undefined);
// Get the bytecode generator state
let obj_ref = obj.borrow();
match &obj_ref.exotic {
ExoticObject::BytecodeGenerator(state) => {
let is_async = state.borrow().is_async;
state.borrow_mut().status = GeneratorStatus::Completed;
drop(obj_ref);
let result = create_generator_result(interp, value, true);
if is_async {
wrap_in_fulfilled_promise(interp, result)
} else {
Ok(result)
}
}
_ => Err(JsError::type_error(
"Generator.prototype.return called on non-generator",
)),
}
}
/// Generator.prototype.throw(exception)
pub fn generator_throw(
interp: &mut Interpreter,
this: JsValue,
args: &[JsValue],
) -> Result<Guarded, JsError> {
let JsValue::Object(obj) = this else {
return Err(JsError::type_error(
"Generator.prototype.throw called on non-object",
));
};
let exception = args.first().cloned().unwrap_or(JsValue::Undefined);
// Get the bytecode generator state
let obj_ref = obj.borrow();
match &obj_ref.exotic {
ExoticObject::BytecodeGenerator(state) => {
let gen_state = state.clone();
let is_async = gen_state.borrow().is_async;
drop(obj_ref); // Release borrow before resuming
// Check if generator is completed or not started
{
let state_ref = gen_state.borrow();
if state_ref.status == GeneratorStatus::Completed {
let guarded = Guarded::from_value(exception, &interp.heap);
return Err(JsError::ThrownValue { guarded });
}
if !state_ref.started {
// Generator hasn't started, just throw
drop(state_ref);
gen_state.borrow_mut().status = GeneratorStatus::Completed;
let guarded = Guarded::from_value(exception, &interp.heap);
return Err(JsError::ThrownValue { guarded });
}
}
// Set the throw value and resume the generator
// The generator will throw this exception at the current yield point
gen_state.borrow_mut().throw_value = Some(exception);
// Resume the generator - it will throw the exception inside
let result = interp.resume_bytecode_generator(&gen_state)?;
if is_async {
wrap_in_fulfilled_promise(interp, result)
} else {
Ok(result)
}
}
_ => Err(JsError::type_error(
"Generator.prototype.throw called on non-generator",
)),
}
}
/// Create a new bytecode generator object
pub fn create_bytecode_generator_object(
interp: &mut Interpreter,
guard: &Guard<JsObject>,
state: BytecodeGeneratorState,
) -> Gc<JsObject> {
let obj = guard.alloc();
{
let mut o = obj.borrow_mut();
o.exotic = ExoticObject::BytecodeGenerator(Rc::new(RefCell::new(state)));
o.prototype = Some(interp.generator_prototype.clone());
}
obj
}
/// Wrap a generator result (Guarded) in a fulfilled Promise.
/// Used by async generators to return Promise<{value, done}>.
fn wrap_in_fulfilled_promise(
interp: &mut Interpreter,
result: Guarded,
) -> Result<Guarded, JsError> {
use super::promise::create_fulfilled_promise;
let guard = interp.heap.create_guard();
// Guard the result value before allocating the promise
if let JsValue::Object(ref obj) = result.value {
guard.guard(obj.cheap_clone());
}
let promise = create_fulfilled_promise(interp, &guard, result.value);
Ok(Guarded::with_guard(JsValue::Object(promise), guard))
}