Support the deprecated_parameter decorator for asynchronous functions.

cirq-core/cirq/_compat.py

@@ -400,23 +400,36 @@ def deprecated_parameter(
     _validate_deadline(deadline)
 
     def decorator(func: Callable) -> Callable:
+        def deprecation_warning():
+            qualname = func.__qualname__ if func_name is None else func_name
+            _warn_or_error(
+                f'The {parameter_desc} parameter of {qualname} was '
+                f'used but is deprecated.\n'
+                f'It will be removed in cirq {deadline}.\n'
+                f'{fix}\n'
+            )
+
         @functools.wraps(func)
         def decorated_func(*args, **kwargs) -> Any:
             if match(args, kwargs):
                 if rewrite is not None:
                     args, kwargs = rewrite(args, kwargs)
+                deprecation_warning()
+            return func(*args, **kwargs)
 
-                qualname = func.__qualname__ if func_name is None else func_name
-                _warn_or_error(
-                    f'The {parameter_desc} parameter of {qualname} was '
-                    f'used but is deprecated.\n'
-                    f'It will be removed in cirq {deadline}.\n'
-                    f'{fix}\n'
-                )
+        @functools.wraps(func)
+        async def async_decorated_func(*args, **kwargs) -> Any:
+            if match(args, kwargs):
+                if rewrite is not None:
+                    args, kwargs = rewrite(args, kwargs)
+                deprecation_warning()
 
-            return func(*args, **kwargs)
+            return await func(*args, **kwargs)
 
-        return decorated_func
+        if inspect.iscoroutinefunction(func):
+            return async_decorated_func
+        else:
+            return decorated_func
 
     return decorator
 
@@ -436,13 +449,12 @@ def deprecate_attributes(module_name: str, deprecated_attributes: Dict[str, Tupl
         will cause a warning for these deprecated attributes.
     """
 
-    for (deadline, _) in deprecated_attributes.values():
+    for deadline, _ in deprecated_attributes.values():
         _validate_deadline(deadline)
 
     module = sys.modules[module_name]
 
     class Wrapped(ModuleType):
-
         __dict__ = module.__dict__
 
         # Workaround for: https://github.com/python/mypy/issues/8083

cirq-core/cirq/_compat_test.py

@@ -26,7 +26,7 @@
 from importlib.machinery import ModuleSpec
 from unittest import mock
 
-
+import duet
 import numpy as np
 import pandas as pd
 import pytest
@@ -263,6 +263,38 @@ def f_with_badly_deprecated_param(new_count):  # pragma: no cover
         # pylint: enable=unused-variable
 
 
+@duet.sync
+async def test_deprecated_parameter_async_function():
+    @deprecated_parameter(
+        deadline='v1.2',
+        fix='Double it yourself.',
+        func_name='test_func',
+        parameter_desc='double_count',
+        match=lambda args, kwargs: 'double_count' in kwargs,
+        rewrite=lambda args, kwargs: (args, {'new_count': kwargs['double_count'] * 2}),
+    )
+    async def f(new_count):
+        return new_count
+
+    # Does not warn on usual use.
+    with cirq.testing.assert_logs(count=0):
+        assert await f(1) == 1
+        assert await f(new_count=1) == 1
+
+    with cirq.testing.assert_deprecated(
+        '_compat_test.py:',
+        'double_count parameter of test_func was used',
+        'will be removed in cirq v1.2',
+        'Double it yourself.',
+        deadline='v1.2',
+    ):
+        # pylint: disable=unexpected-keyword-arg
+        # pylint: disable=no-value-for-parameter
+        assert await f(double_count=1) == 2
+        # pylint: enable=no-value-for-parameter
+        # pylint: enable=unexpected-keyword-arg
+
+
 def test_wrap_module():
     my_module = types.ModuleType('my_module', 'my doc string')
     my_module.foo = 'foo'