Introduce new async-def coroutine syntax (#1657)

esphome/__main__.py

@@ -18,7 +18,7 @@ from esphome.const import (
     CONF_ESPHOME,
     CONF_PLATFORMIO_OPTIONS,
 )
-from esphome.core import CORE, EsphomeError, coroutine, coroutine_with_priority
+from esphome.core import CORE, EsphomeError, coroutine
 from esphome.helpers import indent
 from esphome.util import (
     run_external_command,
@@ -127,15 +127,16 @@ def wrap_to_code(name, comp):
     coro = coroutine(comp.to_code)
 
     @functools.wraps(comp.to_code)
-    @coroutine_with_priority(coro.priority)
+    async def wrapped(conf):
-    def wrapped(conf):
         cg.add(cg.LineComment(f"{name}:"))
         if comp.config_schema is not None:
             conf_str = yaml_util.dump(conf)
             conf_str = conf_str.replace("//", "")
             cg.add(cg.LineComment(indent(conf_str)))
-        yield coro(conf)
+        await coro(conf)
 
+    if hasattr(coro, "priority"):
+        wrapped.priority = coro.priority
     return wrapped
 
 
@@ -610,7 +611,7 @@ def run_esphome(argv):
         try:
             return PRE_CONFIG_ACTIONS[args.command](args)
         except EsphomeError as e:
-            _LOGGER.error(e)
+            _LOGGER.error(e, exc_info=args.verbose)
             return 1
 
     for conf_path in args.configuration:
@@ -628,7 +629,7 @@ def run_esphome(argv):
         try:
             rc = POST_CONFIG_ACTIONS[args.command](args, config)
         except EsphomeError as e:
-            _LOGGER.error(e)
+            _LOGGER.error(e, exc_info=args.verbose)
             return 1
         if rc != 0:
             return rc

esphome/automation.py

@@ -10,7 +10,6 @@ from esphome.const import (
     CONF_TYPE_ID,
     CONF_TIME,
 )
-from esphome.core import coroutine
 from esphome.jsonschema import jschema_extractor
 from esphome.util import Registry
 
@@ -142,27 +141,27 @@ NotCondition = cg.esphome_ns.class_("NotCondition", Condition)
 
 
 @register_condition("and", AndCondition, validate_condition_list)
-def and_condition_to_code(config, condition_id, template_arg, args):
+async def and_condition_to_code(config, condition_id, template_arg, args):
-    conditions = yield build_condition_list(config, template_arg, args)
+    conditions = await build_condition_list(config, template_arg, args)
-    yield cg.new_Pvariable(condition_id, template_arg, conditions)
+    return cg.new_Pvariable(condition_id, template_arg, conditions)
 
 
 @register_condition("or", OrCondition, validate_condition_list)
-def or_condition_to_code(config, condition_id, template_arg, args):
+async def or_condition_to_code(config, condition_id, template_arg, args):
-    conditions = yield build_condition_list(config, template_arg, args)
+    conditions = await build_condition_list(config, template_arg, args)
-    yield cg.new_Pvariable(condition_id, template_arg, conditions)
+    return cg.new_Pvariable(condition_id, template_arg, conditions)
 
 
 @register_condition("not", NotCondition, validate_potentially_and_condition)
-def not_condition_to_code(config, condition_id, template_arg, args):
+async def not_condition_to_code(config, condition_id, template_arg, args):
-    condition = yield build_condition(config, template_arg, args)
+    condition = await build_condition(config, template_arg, args)
-    yield cg.new_Pvariable(condition_id, template_arg, condition)
+    return cg.new_Pvariable(condition_id, template_arg, condition)
 
 
 @register_condition("lambda", LambdaCondition, cv.lambda_)
-def lambda_condition_to_code(config, condition_id, template_arg, args):
+async def lambda_condition_to_code(config, condition_id, template_arg, args):
-    lambda_ = yield cg.process_lambda(config, args, return_type=bool)
+    lambda_ = await cg.process_lambda(config, args, return_type=bool)
-    yield cg.new_Pvariable(condition_id, template_arg, lambda_)
+    return cg.new_Pvariable(condition_id, template_arg, lambda_)
 
 
 @register_condition(
@@ -177,26 +176,26 @@ def lambda_condition_to_code(config, condition_id, template_arg, args):
         }
     ).extend(cv.COMPONENT_SCHEMA),
 )
-def for_condition_to_code(config, condition_id, template_arg, args):
+async def for_condition_to_code(config, condition_id, template_arg, args):
-    condition = yield build_condition(
+    condition = await build_condition(
         config[CONF_CONDITION], cg.TemplateArguments(), []
     )
     var = cg.new_Pvariable(condition_id, template_arg, condition)
-    yield cg.register_component(var, config)
+    await cg.register_component(var, config)
-    templ = yield cg.templatable(config[CONF_TIME], args, cg.uint32)
+    templ = await cg.templatable(config[CONF_TIME], args, cg.uint32)
     cg.add(var.set_time(templ))
-    yield var
+    return var
 
 
 @register_action(
     "delay", DelayAction, cv.templatable(cv.positive_time_period_milliseconds)
 )
-def delay_action_to_code(config, action_id, template_arg, args):
+async def delay_action_to_code(config, action_id, template_arg, args):
     var = cg.new_Pvariable(action_id, template_arg)
-    yield cg.register_component(var, {})
+    await cg.register_component(var, {})
-    template_ = yield cg.templatable(config, args, cg.uint32)
+    template_ = await cg.templatable(config, args, cg.uint32)
     cg.add(var.set_delay(template_))
-    yield var
+    return var
 
 
 @register_action(
@@ -211,16 +210,16 @@ def delay_action_to_code(config, action_id, template_arg, args):
         cv.has_at_least_one_key(CONF_THEN, CONF_ELSE),
     ),
 )
-def if_action_to_code(config, action_id, template_arg, args):
+async def if_action_to_code(config, action_id, template_arg, args):
-    conditions = yield build_condition(config[CONF_CONDITION], template_arg, args)
+    conditions = await build_condition(config[CONF_CONDITION], template_arg, args)
     var = cg.new_Pvariable(action_id, template_arg, conditions)
     if CONF_THEN in config:
-        actions = yield build_action_list(config[CONF_THEN], template_arg, args)
+        actions = await build_action_list(config[CONF_THEN], template_arg, args)
         cg.add(var.add_then(actions))
     if CONF_ELSE in config:
-        actions = yield build_action_list(config[CONF_ELSE], template_arg, args)
+        actions = await build_action_list(config[CONF_ELSE], template_arg, args)
         cg.add(var.add_else(actions))
-    yield var
+    return var
 
 
 @register_action(
@@ -233,12 +232,12 @@ def if_action_to_code(config, action_id, template_arg, args):
         }
     ),
 )
-def while_action_to_code(config, action_id, template_arg, args):
+async def while_action_to_code(config, action_id, template_arg, args):
-    conditions = yield build_condition(config[CONF_CONDITION], template_arg, args)
+    conditions = await build_condition(config[CONF_CONDITION], template_arg, args)
     var = cg.new_Pvariable(action_id, template_arg, conditions)
-    actions = yield build_action_list(config[CONF_THEN], template_arg, args)
+    actions = await build_action_list(config[CONF_THEN], template_arg, args)
     cg.add(var.add_then(actions))
-    yield var
+    return var
 
 
 def validate_wait_until(value):
@@ -253,17 +252,17 @@ def validate_wait_until(value):
 
 
 @register_action("wait_until", WaitUntilAction, validate_wait_until)
-def wait_until_action_to_code(config, action_id, template_arg, args):
+async def wait_until_action_to_code(config, action_id, template_arg, args):
-    conditions = yield build_condition(config[CONF_CONDITION], template_arg, args)
+    conditions = await build_condition(config[CONF_CONDITION], template_arg, args)
     var = cg.new_Pvariable(action_id, template_arg, conditions)
-    yield cg.register_component(var, {})
+    await cg.register_component(var, {})
-    yield var
+    return var
 
 
 @register_action("lambda", LambdaAction, cv.lambda_)
-def lambda_action_to_code(config, action_id, template_arg, args):
+async def lambda_action_to_code(config, action_id, template_arg, args):
-    lambda_ = yield cg.process_lambda(config, args, return_type=cg.void)
+    lambda_ = await cg.process_lambda(config, args, return_type=cg.void)
-    yield cg.new_Pvariable(action_id, template_arg, lambda_)
+    return cg.new_Pvariable(action_id, template_arg, lambda_)
 
 
 @register_action(
@@ -275,54 +274,51 @@ def lambda_action_to_code(config, action_id, template_arg, args):
         }
     ),
 )
-def component_update_action_to_code(config, action_id, template_arg, args):
+async def component_update_action_to_code(config, action_id, template_arg, args):
-    comp = yield cg.get_variable(config[CONF_ID])
+    comp = await cg.get_variable(config[CONF_ID])
-    yield cg.new_Pvariable(action_id, template_arg, comp)
+    return cg.new_Pvariable(action_id, template_arg, comp)
 
 
-@coroutine
+async def build_action(full_config, template_arg, args):
-def build_action(full_config, template_arg, args):
     registry_entry, config = cg.extract_registry_entry_config(
         ACTION_REGISTRY, full_config
     )
     action_id = full_config[CONF_TYPE_ID]
     builder = registry_entry.coroutine_fun
-    yield builder(config, action_id, template_arg, args)
+    ret = await builder(config, action_id, template_arg, args)
+    return ret
 
 
-@coroutine
+async def build_action_list(config, templ, arg_type):
-def build_action_list(config, templ, arg_type):
     actions = []
     for conf in config:
-        action = yield build_action(conf, templ, arg_type)
+        action = await build_action(conf, templ, arg_type)
         actions.append(action)
-    yield actions
+    return actions
 
 
-@coroutine
+async def build_condition(full_config, template_arg, args):
-def build_condition(full_config, template_arg, args):
     registry_entry, config = cg.extract_registry_entry_config(
         CONDITION_REGISTRY, full_config
     )
     action_id = full_config[CONF_TYPE_ID]
     builder = registry_entry.coroutine_fun
-    yield builder(config, action_id, template_arg, args)
+    ret = await builder(config, action_id, template_arg, args)
+    return ret
 
 
-@coroutine
+async def build_condition_list(config, templ, args):
-def build_condition_list(config, templ, args):
     conditions = []
     for conf in config:
-        condition = yield build_condition(conf, templ, args)
+        condition = await build_condition(conf, templ, args)
         conditions.append(condition)
-    yield conditions
+    return conditions
 
 
-@coroutine
+async def build_automation(trigger, args, config):
-def build_automation(trigger, args, config):
     arg_types = [arg[0] for arg in args]
     templ = cg.TemplateArguments(*arg_types)
     obj = cg.new_Pvariable(config[CONF_AUTOMATION_ID], templ, trigger)
-    actions = yield build_action_list(config[CONF_THEN], templ, args)
+    actions = await build_action_list(config[CONF_THEN], templ, args)
     cg.add(obj.add_actions(actions))
-    yield obj
+    return obj

esphome/components/ota/__init__.py

@@ -32,12 +32,12 @@ CONFIG_SCHEMA = cv.Schema(
 
 
 @coroutine_with_priority(50.0)
-def to_code(config):
+async def to_code(config):
     var = cg.new_Pvariable(config[CONF_ID])
     cg.add(var.set_port(config[CONF_PORT]))
     cg.add(var.set_auth_password(config[CONF_PASSWORD]))
 
-    yield cg.register_component(var, config)
+    await cg.register_component(var, config)
 
     if config[CONF_SAFE_MODE]:
         condition = var.should_enter_safe_mode(

esphome/core/__init__.py

@@ -1,24 +1,23 @@
-import functools
-import heapq
-import inspect
 import logging
-
 import math
 import os
 import re
-
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Set, Tuple
-# pylint: disable=unused-import, wrong-import-order
-from typing import Any, Dict, List, Optional, Set, TYPE_CHECKING  # noqa
 
 from esphome.const import (
     CONF_ARDUINO_VERSION,
-    SOURCE_FILE_EXTENSIONS,
     CONF_COMMENT,
     CONF_ESPHOME,
     CONF_USE_ADDRESS,
     CONF_ETHERNET,
     CONF_WIFI,
+    SOURCE_FILE_EXTENSIONS,
 )
+from esphome.coroutine import FakeAwaitable as _FakeAwaitable
+from esphome.coroutine import FakeEventLoop as _FakeEventLoop
+
+# pylint: disable=unused-import
+from esphome.coroutine import coroutine, coroutine_with_priority  # noqa
 from esphome.helpers import ensure_unique_string, is_hassio
 from esphome.util import OrderedDict
 
@@ -431,64 +430,6 @@ class Library:
         return NotImplemented
 
 
-def coroutine(func):
-    return coroutine_with_priority(0.0)(func)
-
-
-def coroutine_with_priority(priority):
-    def decorator(func):
-        if getattr(func, "_esphome_coroutine", False):
-            # If func is already a coroutine, do not re-wrap it (performance)
-            return func
-
-        @functools.wraps(func)
-        def _wrapper_generator(*args, **kwargs):
-            instance_id = kwargs.pop("__esphome_coroutine_instance__")
-            if not inspect.isgeneratorfunction(func):
-                # If func is not a generator, return result immediately
-                yield func(*args, **kwargs)
-                # pylint: disable=protected-access
-                CORE._remove_coroutine(instance_id)
-                return
-            gen = func(*args, **kwargs)
-            var = None
-            try:
-                while True:
-                    var = gen.send(var)
-                    if inspect.isgenerator(var):
-                        # Yielded generator, equivalent to 'yield from'
-                        x = None
-                        for x in var:
-                            yield None
-                        # Last yield value is the result
-                        var = x
-                    else:
-                        yield var
-            except StopIteration:
-                # Stopping iteration
-                yield var
-            # pylint: disable=protected-access
-            CORE._remove_coroutine(instance_id)
-
-        @functools.wraps(func)
-        def wrapper(*args, **kwargs):
-            import random
-
-            instance_id = random.randint(0, 2 ** 32)
-            kwargs["__esphome_coroutine_instance__"] = instance_id
-            gen = _wrapper_generator(*args, **kwargs)
-            # pylint: disable=protected-access
-            CORE._add_active_coroutine(instance_id, gen)
-            return gen
-
-        # pylint: disable=protected-access
-        wrapper._esphome_coroutine = True
-        wrapper.priority = priority
-        return wrapper
-
-    return decorator
-
-
 def find_source_files(file):
     files = set()
     directory = os.path.abspath(os.path.dirname(file))
@@ -527,7 +468,7 @@ class EsphomeCore:
         # The pending tasks in the task queue (mostly for C++ generation)
         # This is a priority queue (with heapq)
         # Each item is a tuple of form: (-priority, unique number, task)
-        self.pending_tasks = []
+        self.event_loop = _FakeEventLoop()
         # Task counter for pending tasks
         self.task_counter = 0
         # The variable cache, for each ID this holds a MockObj of the variable obj
@@ -542,9 +483,6 @@ class EsphomeCore:
         self.build_flags: Set[str] = set()
         # A set of defines to set for the compile process in esphome/core/defines.h
         self.defines: Set["Define"] = set()
-        # A dictionary of started coroutines, used to warn when a coroutine was not
-        # awaited.
-        self.active_coroutines: Dict[int, Any] = {}
         # A set of strings of names of loaded integrations, used to find namespace ID conflicts
         self.loaded_integrations = set()
         # A set of component IDs to track what Component subclasses are declared
@@ -561,7 +499,7 @@ class EsphomeCore:
         self.board = None
         self.raw_config = None
         self.config = None
-        self.pending_tasks = []
+        self.event_loop = _FakeEventLoop()
         self.task_counter = 0
         self.variables = {}
         self.main_statements = []
@@ -569,7 +507,6 @@ class EsphomeCore:
         self.libraries = []
         self.build_flags = set()
         self.defines = set()
-        self.active_coroutines = {}
         self.loaded_integrations = set()
         self.component_ids = set()
 
@@ -596,12 +533,6 @@ class EsphomeCore:
 
         return None
 
-    def _add_active_coroutine(self, instance_id, obj):
-        self.active_coroutines[instance_id] = obj
-
-    def _remove_coroutine(self, instance_id):
-        self.active_coroutines.pop(instance_id)
-
     @property
     def arduino_version(self) -> str:
         if self.config is None:
@@ -657,50 +588,13 @@ class EsphomeCore:
         return self.esp_platform == "ESP32"
 
     def add_job(self, func, *args, **kwargs):
-        coro = coroutine(func)
+        self.event_loop.add_job(func, *args, **kwargs)
-        task = coro(*args, **kwargs)
-        item = (-coro.priority, self.task_counter, task)
-        self.task_counter += 1
-        heapq.heappush(self.pending_tasks, item)
-        return task
 
     def flush_tasks(self):
-        i = 0
-        while self.pending_tasks:
-            i += 1
-            if i > 1000000:
-                raise EsphomeError("Circular dependency detected!")
-
-            inv_priority, num, task = heapq.heappop(self.pending_tasks)
-            priority = -inv_priority
-            _LOGGER.debug("Running %s (num %s)", task, num)
         try:
-                next(task)
+            self.event_loop.flush_tasks()
-                # Decrease priority over time, so that if this task is blocked
+        except RuntimeError as e:
-                # due to a dependency others will clear the dependency
+            raise EsphomeError(str(e)) from e
-                # This could be improved with a less naive approach
-                priority -= 1
-                item = (-priority, num, task)
-                heapq.heappush(self.pending_tasks, item)
-            except StopIteration:
-                _LOGGER.debug(" -> finished")
-
-        # Print not-awaited coroutines
-        for obj in self.active_coroutines.values():
-            _LOGGER.warning(
-                "Coroutine '%s' %s was never awaited with 'yield'.", obj.__name__, obj
-            )
-            _LOGGER.warning("Please file a bug report with your configuration.")
-        if self.active_coroutines:
-            raise EsphomeError()
-        if self.component_ids:
-            comps = ", ".join(f"'{x}'" for x in self.component_ids)
-            _LOGGER.warning(
-                "Components %s were never registered. Please create a bug report", comps
-            )
-            _LOGGER.warning("with your configuration.")
-            raise EsphomeError()
-        self.active_coroutines.clear()
 
     def add(self, expression):
         from esphome.cpp_generator import Expression, Statement, statement
@@ -779,25 +673,35 @@ class EsphomeCore:
         _LOGGER.debug("Adding define: %s", define)
         return define
 
-    def get_variable(self, id):
+    def _get_variable_generator(self, id):
+        while True:
+            try:
+                return self.variables[id]
+            except KeyError:
+                _LOGGER.debug("Waiting for variable %s (%r)", id, id)
+                yield
+
+    async def get_variable(self, id) -> "MockObj":
         if not isinstance(id, ID):
             raise ValueError(f"ID {id!r} must be of type ID!")
-        while True:
+        # Fast path, check if already registered without awaiting
         if id in self.variables:
-                yield self.variables[id]
+            return self.variables[id]
-                return
+        return await _FakeAwaitable(self._get_variable_generator(id))
-            _LOGGER.debug("Waiting for variable %s (%r)", id, id)
-            yield None
 
-    def get_variable_with_full_id(self, id):
+    def _get_variable_with_full_id_generator(self, id):
         while True:
             if id in self.variables:
                 for k, v in self.variables.items():
                     if k == id:
-                        yield (k, v)
+                        return (k, v)
-                        return
             _LOGGER.debug("Waiting for variable %s", id)
-            yield None, None
+            yield
+
+    async def get_variable_with_full_id(self, id: ID) -> Tuple[ID, "MockObj"]:
+        if not isinstance(id, ID):
+            raise ValueError(f"ID {id!r} must be of type ID!")
+        return await _FakeAwaitable(self._get_variable_with_full_id_generator(id))
 
     def register_variable(self, id, obj):
         if id in self.variables:

esphome/core/config.py

@@ -233,7 +233,7 @@ def include_file(path, basename):
 
 
 @coroutine_with_priority(-1000.0)
-def add_includes(includes):
+async def add_includes(includes):
     # Add includes at the very end, so that the included files can access global variables
     for include in includes:
         path = CORE.relative_config_path(include)
@@ -249,7 +249,7 @@ def add_includes(includes):
 
 
 @coroutine_with_priority(-1000.0)
-def _esp8266_add_lwip_type():
+async def _esp8266_add_lwip_type():
     # If any component has already set this, do not change it
     if any(
         flag.startswith("-DPIO_FRAMEWORK_ARDUINO_LWIP2_") for flag in CORE.build_flags
@@ -271,25 +271,25 @@ def _esp8266_add_lwip_type():
 
 
 @coroutine_with_priority(30.0)
-def _add_automations(config):
+async def _add_automations(config):
     for conf in config.get(CONF_ON_BOOT, []):
         trigger = cg.new_Pvariable(conf[CONF_TRIGGER_ID], conf.get(CONF_PRIORITY))
-        yield cg.register_component(trigger, conf)
+        await cg.register_component(trigger, conf)
-        yield automation.build_automation(trigger, [], conf)
+        await automation.build_automation(trigger, [], conf)
 
     for conf in config.get(CONF_ON_SHUTDOWN, []):
         trigger = cg.new_Pvariable(conf[CONF_TRIGGER_ID])
-        yield cg.register_component(trigger, conf)
+        await cg.register_component(trigger, conf)
-        yield automation.build_automation(trigger, [], conf)
+        await automation.build_automation(trigger, [], conf)
 
     for conf in config.get(CONF_ON_LOOP, []):
         trigger = cg.new_Pvariable(conf[CONF_TRIGGER_ID])
-        yield cg.register_component(trigger, conf)
+        await cg.register_component(trigger, conf)
-        yield automation.build_automation(trigger, [], conf)
+        await automation.build_automation(trigger, [], conf)
 
 
 @coroutine_with_priority(100.0)
-def to_code(config):
+async def to_code(config):
     cg.add_global(cg.global_ns.namespace("esphome").using)
     cg.add(
         cg.App.pre_setup(

esphome/coroutine.py

@@ -0,0 +1,252 @@
+"""
+ESPHome's coroutine system.
+
+The Problem: When running the code generationg, components can depend on variables being registered.
+For example, an i2c-based sensor would need the i2c bus component to first be declared before the
+codegen can emit code using that variable (or otherwise the C++ won't compile).
+
+ESPHome's codegen system solves this by using coroutine-like methods. When a component depends on
+a variable, it waits for it to be registered using `await cg.get_variable()`. If the variable
+hasn't been registered yet, control will be yielded back to another component until the variable
+is registered. This leads to a topological sort, solving the dependency problem.
+
+Importantly, ESPHome only uses the coroutine *syntax*, no actual asyncio event loop is running in
+the background. This is so that we can ensure the order of execution is constant for the same
+YAML configuration, thus main.cpp only has to be recompiled if the configuration actually changes.
+
+There are two syntaxes for ESPHome coroutines ("old style" vs "new style" coroutines).
+
+"new style" - This is very much like coroutines you might be used to:
+
+```py
+async def my_coroutine(config):
+    var = await cg.get_variable(config[CONF_ID])
+    await some_other_coroutine(xyz)
+    return var
+```
+
+new style coroutines are `async def` methods that use `await` to await the result of another coroutine,
+and can return values using a `return` statement.
+
+"old style" - This was a hack for when ESPHome still had to run on python 2, but is still compatible
+
+```py
+@coroutine
+def my_coroutine(config):
+    var = yield cg.get_variable(config[CONF_ID])
+    yield some_other_coroutine(xyz)
+    yield var
+```
+
+Here everything is combined in `yield` expressions. You await other coroutines using `yield` and
+the last `yield` expression defines what is returned.
+"""
+
+import collections
+import functools
+import heapq
+import inspect
+import logging
+import types
+from typing import Any, Awaitable, Callable, Generator, Iterator, List, Tuple
+
+_LOGGER = logging.getLogger(__name__)
+
+
+def coroutine(func: Callable[..., Any]) -> Callable[..., Awaitable[Any]]:
+    """Decorator to apply to methods to convert them to ESPHome coroutines."""
+    if getattr(func, "_esphome_coroutine", False):
+        # If func is already a coroutine, do not re-wrap it (performance)
+        return func
+    if inspect.isasyncgenfunction(func):
+        # Trade-off: In ESPHome, there's not really a use-case for async generators.
+        # and during the transition to new-style syntax it will happen that a `yield`
+        # is not replaced properly, so don't accept async generators.
+        raise ValueError(
+            f"Async generator functions are not allowed. "
+            f"Please check whether you've replaced all yields with awaits/returns. "
+            f"See {func} in {func.__module__}"
+        )
+    if inspect.iscoroutinefunction(func):
+        # A new-style async-def coroutine function, no conversion needed.
+        return func
+
+    if inspect.isgeneratorfunction(func):
+
+        @functools.wraps(func)
+        def coro(*args, **kwargs):
+            gen = func(*args, **kwargs)
+            ret = yield from _flatten_generator(gen)
+            return ret
+
+    else:
+        # A "normal" function with no `yield` statements, convert to generator
+        # that includes a yield just so it's also a generator function
+        @functools.wraps(func)
+        def coro(*args, **kwargs):
+            res = func(*args, **kwargs)
+            yield
+            return res
+
+    # Add coroutine internal python flag so that it can be awaited from new-style coroutines.
+    coro = types.coroutine(coro)
+    # pylint: disable=protected-access
+    coro._esphome_coroutine = True
+    return coro
+
+
+def coroutine_with_priority(priority: float):
+    """Decorator to apply to functions to convert them to ESPHome coroutines.
+
+    :param priority: priority with which to schedule the coroutine, higher priorities run first.
+    """
+
+    def decorator(func):
+        coro = coroutine(func)
+        coro.priority = priority
+        return coro
+
+    return decorator
+
+
+def _flatten_generator(gen: Generator[Any, Any, Any]):
+    to_send = None
+    while True:
+        try:
+            # Run until next yield expression
+            val = gen.send(to_send)
+        except StopIteration as e:
+            # return statement or end of function
+
+            # From py3.3, return with a value is allowed in generators,
+            # and return value is transported in the value field of the exception.
+            # If we find a value in the exception, use that as the return value,
+            # otherwise use the value from the last yield statement ("old style")
+            ret = to_send if e.value is None else e.value
+            return ret
+
+        if isinstance(val, collections.abc.Awaitable):
+            # yielded object that is awaitable (like `yield some_new_style_method()`)
+            # yield from __await__() like actual coroutines would.
+            to_send = yield from val.__await__()
+        elif inspect.isgenerator(val):
+            # Old style, like `yield cg.get_variable()`
+            to_send = yield from _flatten_generator(val)
+        else:
+            # Could be the last expression from this generator, record this as the return value
+            to_send = val
+            # perform a yield so that expressions like `while some_condition(): yield None`
+            # do not run without yielding control back to the top
+            yield
+
+
+class FakeAwaitable:
+    """Convert a generator to an awaitable object.
+
+    Needed for internals of `cg.get_variable`. There we can't use @coroutine because
+    native coroutines await from types.coroutine() directly without yielding back control to the top
+    (likely as a performance enhancement).
+
+    If we instead wrap the generator in this FakeAwaitable, control is yielded back to the top
+    (reason unknown).
+    """
+
+    def __init__(self, gen: Generator[Any, Any, Any]) -> None:
+        self._gen = gen
+
+    def __await__(self):
+        ret = yield from self._gen
+        return ret
+
+
+@functools.total_ordering
+class _Task:
+    def __init__(
+        self,
+        priority: float,
+        id_number: int,
+        iterator: Iterator[None],
+        original_function: Any,
+    ):
+        self.priority = priority
+        self.id_number = id_number
+        self.iterator = iterator
+        self.original_function = original_function
+
+    def with_priority(self, priority: float) -> "_Task":
+        return _Task(priority, self.id_number, self.iterator, self.original_function)
+
+    @property
+    def _cmp_tuple(self) -> Tuple[float, int]:
+        return (-self.priority, self.id_number)
+
+    def __eq__(self, other):
+        return self._cmp_tuple == other._cmp_tuple
+
+    def __ne__(self, other):
+        return not (self == other)
+
+    def __lt__(self, other):
+        return self._cmp_tuple < other._cmp_tuple
+
+
+class FakeEventLoop:
+    """Emulate an asyncio EventLoop to run some registered coroutine jobs in sequence."""
+
+    def __init__(self):
+        self._pending_tasks: List[_Task] = []
+        self._task_counter = 0
+
+    def add_job(self, func, *args, **kwargs):
+        """Add a job to the task queue,
+
+        Optionally retrieves priority from the function object, and schedules according to that.
+        """
+        if inspect.iscoroutine(func):
+            raise ValueError("Can only add coroutine functions, not coroutine objects")
+        if inspect.iscoroutinefunction(func):
+            coro = func
+            gen = coro(*args, **kwargs).__await__()
+        else:
+            coro = coroutine(func)
+            gen = coro(*args, **kwargs)
+        prio = getattr(coro, "priority", 0.0)
+        task = _Task(prio, self._task_counter, gen, func)
+        self._task_counter += 1
+        heapq.heappush(self._pending_tasks, task)
+
+    def flush_tasks(self):
+        """Run until all tasks have been completed.
+
+        :raises RuntimeError: if a deadlock is detected.
+        """
+        i = 0
+        while self._pending_tasks:
+            i += 1
+            if i > 1000000:
+                # Detect deadlock/circular dependency by measuring how many times tasks have been
+                # executed. On the big tests/test1.yaml we only get to a fraction of this, so
+                # this shouldn't be a problem.
+                raise RuntimeError(
+                    "Circular dependency detected! "
+                    "Please run with -v option to see what functions failed to "
+                    "complete."
+                )
+
+            task: _Task = heapq.heappop(self._pending_tasks)
+            _LOGGER.debug(
+                "Running %s in %s (num %s)",
+                task.original_function.__qualname__,
+                task.original_function.__module__,
+                task.id_number,
+            )
+
+            try:
+                next(task.iterator)
+                # Decrease priority over time, so that if this task is blocked
+                # due to a dependency others will clear the dependency
+                # This could be improved with a less naive approach
+                new_task = task.with_priority(task.priority - 1)
+                heapq.heappush(self._pending_tasks, new_task)
+            except StopIteration:
+                _LOGGER.debug(" -> finished")

esphome/cpp_generator.py

@@ -549,8 +549,7 @@ def add_define(name: str, value: SafeExpType = None):
         CORE.add_define(Define(name, safe_exp(value)))
 
 
-@coroutine
+async def get_variable(id_: ID) -> "MockObj":
-def get_variable(id_: ID) -> Generator["MockObj", None, None]:
     """
     Wait for the given ID to be defined in the code generation and
     return it as a MockObj.
@@ -560,12 +559,10 @@ def get_variable(id_: ID) -> Generator["MockObj", None, None]:
     :param id_: The ID to retrieve
     :return: The variable as a MockObj.
     """
-    var = yield CORE.get_variable(id_)
+    return await CORE.get_variable(id_)
-    yield var
 
 
-@coroutine
+async def get_variable_with_full_id(id_: ID) -> Tuple[ID, "MockObj"]:
-def get_variable_with_full_id(id_: ID) -> Generator[Tuple[ID, "MockObj"], None, None]:
     """
     Wait for the given ID to be defined in the code generation and
     return it as a MockObj.
@@ -575,8 +572,7 @@ def get_variable_with_full_id(id_: ID) -> Generator[Tuple[ID, "MockObj"], None,
     :param id_: The ID to retrieve
     :return: The variable as a MockObj.
     """
-    full_id, var = yield CORE.get_variable_with_full_id(id_)
+    return await CORE.get_variable_with_full_id(id_)
-    yield full_id, var
 
 
 @coroutine
@@ -604,7 +600,7 @@ def process_lambda(
         return
     parts = value.parts[:]
     for i, id in enumerate(value.requires_ids):
-        full_id, var = yield CORE.get_variable_with_full_id(id)
+        full_id, var = yield get_variable_with_full_id(id)
         if (
             full_id is not None
             and isinstance(full_id.type, MockObjClass)
@@ -675,6 +671,9 @@ class MockObj(Expression):
         self.op = op
 
     def __getattr__(self, attr: str) -> "MockObj":
+        # prevent python dunder methods being replaced by mock objects
+        if attr.startswith("__"):
+            raise AttributeError()
         next_op = "."
         if attr.startswith("P") and self.op not in ["::", ""]:
             attr = attr[1:]

requirements_test.txt

@@ -10,5 +10,6 @@ pre-commit
 pytest==6.2.4
 pytest-cov==2.11.1
 pytest-mock==3.5.1
+pytest-asyncio==0.14.0
 asyncmock==0.4.2
 hypothesis==5.21.0

tests/unit_tests/test_core.py

@@ -490,11 +490,15 @@ class TestEsphomeCore:
 
     def test_reset(self, target):
         """Call reset on target and compare to new instance"""
-        other = core.EsphomeCore()
+        other = core.EsphomeCore().__dict__
 
         target.reset()
+        t = target.__dict__
+        # ignore event loop
+        del other["event_loop"]
+        del t["event_loop"]
 
-        assert target.__dict__ == other.__dict__
+        assert t == other
 
     def test_address__none(self, target):
         target.config = {}

tests/unit_tests/test_cpp_helpers.py

@@ -6,25 +6,24 @@ from esphome import const
 from esphome.cpp_generator import MockObj
 
 
-def test_gpio_pin_expression__conf_is_none(monkeypatch):
+@pytest.mark.asyncio
-    target = ch.gpio_pin_expression(None)
+async def test_gpio_pin_expression__conf_is_none(monkeypatch):
-
+    actual = await ch.gpio_pin_expression(None)
-    actual = next(target)
 
     assert actual is None
 
 
-def test_gpio_pin_expression__new_pin(monkeypatch):
+@pytest.mark.asyncio
-    target = ch.gpio_pin_expression(
+async def test_gpio_pin_expression__new_pin(monkeypatch):
+    actual = await ch.gpio_pin_expression(
         {const.CONF_NUMBER: 42, const.CONF_MODE: "input", const.CONF_INVERTED: False}
     )
 
-    actual = next(target)
-
     assert isinstance(actual, MockObj)
 
 
-def test_register_component(monkeypatch):
+@pytest.mark.asyncio
+async def test_register_component(monkeypatch):
     var = Mock(base="foo.bar")
 
     app_mock = Mock(register_component=Mock(return_value=var))
@@ -36,9 +35,7 @@ def test_register_component(monkeypatch):
     add_mock = Mock()
     monkeypatch.setattr(ch, "add", add_mock)
 
-    target = ch.register_component(var, {})
+    actual = await ch.register_component(var, {})
-
-    actual = next(target)
 
     assert actual is var
     add_mock.assert_called_once()
@@ -46,18 +43,19 @@ def test_register_component(monkeypatch):
     assert core_mock.component_ids == []
 
 
-def test_register_component__no_component_id(monkeypatch):
+@pytest.mark.asyncio
+async def test_register_component__no_component_id(monkeypatch):
     var = Mock(base="foo.eek")
 
     core_mock = Mock(component_ids=["foo.bar"])
     monkeypatch.setattr(ch, "CORE", core_mock)
 
     with pytest.raises(ValueError, match="Component ID foo.eek was not declared to"):
-        target = ch.register_component(var, {})
+        await ch.register_component(var, {})
-        next(target)
 
 
-def test_register_component__with_setup_priority(monkeypatch):
+@pytest.mark.asyncio
+async def test_register_component__with_setup_priority(monkeypatch):
     var = Mock(base="foo.bar")
 
     app_mock = Mock(register_component=Mock(return_value=var))
@@ -69,7 +67,7 @@ def test_register_component__with_setup_priority(monkeypatch):
     add_mock = Mock()
     monkeypatch.setattr(ch, "add", add_mock)
 
-    target = ch.register_component(
+    actual = await ch.register_component(
         var,
         {
             const.CONF_SETUP_PRIORITY: "123",
@@ -77,8 +75,6 @@ def test_register_component__with_setup_priority(monkeypatch):
         },
     )
 
-    actual = next(target)
-
     assert actual is var
     add_mock.assert_called()
     assert add_mock.call_count == 3