asyncio: Add Task methods to get tasks closer to CPython.

Adds methods that are in CPython, such as `exception`, `result`,
`get_coro`, `cancelled`, `add_done_callback`, and
`remove_done_callback`.

Also adds support for the unary hash so tasks may be collected in
a python set.

extmod/modasyncio.c

@@ -46,6 +46,12 @@
     (task)->state == TASK_STATE_DONE_NOT_WAITED_ON \
     || (task)->state == TASK_STATE_DONE_WAS_WAITED_ON)
 
+#define IS_CANCELLED_ERROR(error) ( \
+    mp_obj_is_subclass_fast( \
+    MP_OBJ_FROM_PTR(mp_obj_get_type(error)), \
+    mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_CancelledError)) \
+    ))
+
 typedef struct _mp_obj_task_t {
     mp_pairheap_t pairheap;
     mp_obj_t coro;
@@ -202,6 +208,114 @@ STATIC mp_obj_t task_done(mp_obj_t self_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(task_done_obj, task_done);
 
+STATIC mp_obj_t task_add_done_callback(mp_obj_t self_in, mp_obj_t callback) {
+    assert(mp_obj_is_callable(callback));
+    mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (TASK_IS_DONE(self)) {
+        // In CPython the callbacks are not immediately called and are instead
+        // called by the event loop.  However, MicroPython's event loop doesn't
+        // support `call_soon` to handle callback processing.
+        //
+        // Because of this, it's close enough to call the callback immediately.
+
+        mp_call_function_2(callback, self_in, self->data);
+        return mp_const_none;
+    }
+
+    if (self->state != mp_const_true) {
+        // Tasks SHOULD support more than one callback per CPython but to reduce
+        // the surface area of this change tasks can currently only support one.
+        mp_raise_msg(&mp_type_RuntimeError, MP_ERROR_TEXT(">1 callback unsupported"));
+    }
+
+    self->state = callback;
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(task_add_done_callback_obj, task_add_done_callback);
+
+STATIC mp_obj_t task_remove_done_callback(mp_obj_t self_in, mp_obj_t callback) {
+    mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (callback != self->state) {
+        // If the callback isn't a match we can count this as removing 0 callbacks
+        return mp_obj_new_int(0);
+    }
+
+    self->state = mp_const_true;
+    return mp_obj_new_int(1);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(task_remove_done_callback_obj, task_remove_done_callback);
+
+STATIC mp_obj_t task_get_coro(mp_obj_t self_in) {
+    mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
+    return MP_OBJ_FROM_PTR(self->coro);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(task_get_coro_obj, task_get_coro);
+
+STATIC mp_obj_t task_exception(mp_obj_t self_in) {
+    mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (!TASK_IS_DONE(self)) {
+        mp_obj_t error_type = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_InvalidStateError));
+        nlr_raise(mp_make_raise_obj(error_type));
+    }
+
+    // If the exception is a cancelled error then we should raise it
+    if (IS_CANCELLED_ERROR(self->data)) {
+        nlr_raise(mp_make_raise_obj(self->data));
+    }
+
+    // If it's a StopIteration we should should return none
+    if (mp_obj_is_subclass_fast(MP_OBJ_FROM_PTR(mp_obj_get_type(self->data)), MP_OBJ_FROM_PTR(&mp_type_StopIteration))) {
+        return mp_const_none;
+    }
+
+    if (!mp_obj_is_exception_instance(self->data)) {
+        return mp_const_none;
+    }
+
+    return self->data;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(task_exception_obj, task_exception);
+
+STATIC mp_obj_t task_result(mp_obj_t self_in) {
+    mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (!TASK_IS_DONE(self)) {
+        mp_obj_t error_type = mp_obj_dict_get(asyncio_context, MP_OBJ_NEW_QSTR(MP_QSTR_InvalidStateError));
+        nlr_raise(mp_make_raise_obj(error_type));
+    }
+
+    // If `exception()` returns anything we raise that
+    mp_obj_t exception_obj = task_exception(self_in);
+    if (exception_obj != mp_const_none) {
+        nlr_raise(mp_make_raise_obj(exception_obj));
+    }
+
+    // If not StopIteration, bail early
+    if (!mp_obj_is_subclass_fast(MP_OBJ_FROM_PTR(mp_obj_get_type(self->data)), MP_OBJ_FROM_PTR(&mp_type_StopIteration))) {
+        return mp_const_none;
+    }
+
+    return mp_obj_exception_get_value(self->data);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(task_result_obj, task_result);
+
+STATIC mp_obj_t task_cancelled(mp_obj_t self_in) {
+    mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
+
+    if (!TASK_IS_DONE(self)) {
+        // If task isn't done it can't possibly be cancelled, and would instead
+        // be considered "cancelling" even if a cancel was requested until it
+        // has fully completed.
+        return mp_obj_new_bool(false);
+    }
+
+    return mp_obj_new_bool(IS_CANCELLED_ERROR(self->data));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(task_cancelled_obj, task_cancelled);
+
 STATIC mp_obj_t task_cancel(mp_obj_t self_in) {
     mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
     // Check if task is already finished.
@@ -276,6 +390,24 @@ STATIC void task_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
         } else if (attr == MP_QSTR___await__) {
             dest[0] = MP_OBJ_FROM_PTR(&task_await_obj);
             dest[1] = self_in;
+        } else if (attr == MP_QSTR_add_done_callback) {
+            dest[0] = MP_OBJ_FROM_PTR(&task_add_done_callback_obj);
+            dest[1] = self_in;
+        } else if (attr == MP_QSTR_remove_done_callback) {
+            dest[0] = MP_OBJ_FROM_PTR(&task_remove_done_callback_obj);
+            dest[1] = self_in;
+        } else if (attr == MP_QSTR_get_coro) {
+            dest[0] = MP_OBJ_FROM_PTR(&task_get_coro_obj);
+            dest[1] = self_in;
+        } else if (attr == MP_QSTR_result) {
+            dest[0] = MP_OBJ_FROM_PTR(&task_result_obj);
+            dest[1] = self_in;
+        } else if (attr == MP_QSTR_exception) {
+            dest[0] = MP_OBJ_FROM_PTR(&task_exception_obj);
+            dest[1] = self_in;
+        } else if (attr == MP_QSTR_cancelled) {
+            dest[0] = MP_OBJ_FROM_PTR(&task_cancelled_obj);
+            dest[1] = self_in;
         }
     } else if (dest[1] != MP_OBJ_NULL) {
         // Store
@@ -289,6 +421,15 @@ STATIC void task_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     }
 }
 
+STATIC mp_obj_t task_unary_op(mp_unary_op_t op, mp_obj_t o_in) {
+    switch (op) {
+        case MP_UNARY_OP_HASH:
+            return MP_OBJ_NEW_SMALL_INT((mp_uint_t)o_in);
+        default:
+            return MP_OBJ_NULL;      // op not supported
+    }
+}
+
 STATIC mp_obj_t task_getiter(mp_obj_t self_in, mp_obj_iter_buf_t *iter_buf) {
     (void)iter_buf;
     mp_obj_task_t *self = MP_OBJ_TO_PTR(self_in);
@@ -337,7 +478,8 @@ STATIC MP_DEFINE_CONST_OBJ_TYPE(
     MP_TYPE_FLAG_ITER_IS_CUSTOM,
     make_new, task_make_new,
     attr, task_attr,
-    iter, &task_getiter_iternext
+    iter, &task_getiter_iternext,
+    unary_op, task_unary_op
     );
 
 /******************************************************************************/