Remove _get_async_param from compat

`_get_async_param()` was added in Twisted 18.9.0 to mitigate an issue
where Python 3.7 introduced the `async` keyword which caused problems
where variables were trying to use that name also.

There is no need to maintain backwards compatability for Python 3.6 and
older, which may have been using the 'async' kwargs argument. Twisted
today only supports Python 3.8+ and we can rely on the 'isAsync'
function argument instead.

Supplying 'async' argument to `_get_async_param` has been deprecated
since 18.9.0 and is now removed with this commit.

src/twisted/conch/manhole.py

@@ -23,7 +23,6 @@
 
 from twisted.conch import recvline
 from twisted.internet import defer
-from twisted.python.compat import _get_async_param
 from twisted.python.htmlizer import TokenPrinter
 from twisted.python.monkey import MonkeyPatcher
 
@@ -161,8 +160,7 @@ def _ebDisplayDeferred(self, failure, k, obj):
         del self._pendingDeferreds[id(obj)]
         return failure
 
-    def write(self, data, isAsync=None, **kwargs):
-        isAsync = _get_async_param(isAsync, **kwargs)
+    def write(self, data, isAsync=None):
         self.handler.addOutput(data, isAsync)
 
 
@@ -239,8 +237,7 @@ def _needsNewline(self):
         w = self.terminal.lastWrite
         return not w.endswith(b"\n") and not w.endswith(b"\x1bE")
 
-    def addOutput(self, data, isAsync=None, **kwargs):
-        isAsync = _get_async_param(isAsync, **kwargs)
+    def addOutput(self, data, isAsync=None):
         if isAsync:
             self.terminal.eraseLine()
             self.terminal.cursorBackward(len(self.lineBuffer) + len(self.ps[self.pn]))

src/twisted/mail/imap4.py

@@ -80,7 +80,6 @@
 from twisted.protocols import basic, policies
 from twisted.python import log, text
 from twisted.python.compat import (
-    _get_async_param,
     _matchingString,
     iterbytes,
     nativeString,
@@ -1076,8 +1075,7 @@ def sendPositiveResponse(self, tag=None, message=b""):
     def sendNegativeResponse(self, tag=None, message=b""):
         self._respond(b"NO", tag, message)
 
-    def sendUntaggedResponse(self, message, isAsync=None, **kwargs):
-        isAsync = _get_async_param(isAsync, **kwargs)
+    def sendUntaggedResponse(self, message, isAsync=None):
         if not isAsync or (self.blocked is None):
             self._respond(message, None, None)
         else:

src/twisted/newsfragments/12130.removal

@@ -0,0 +1 @@
+twisted.conch.manhole.ManholeInterpreter.write, twisted.conch.manhole.ManholeInterpreter.addOutput, twisted.mail.imap4.IMAP4Server.sendUntaggedResponse `async` argument, deprecated since 18.9.0, has been removed.

src/twisted/python/compat.py

@@ -27,7 +27,6 @@
 import platform
 import socket
 import urllib.parse as urllib_parse
-import warnings
 from collections.abc import Sequence
 from functools import reduce
 from html import escape
@@ -497,35 +496,6 @@ def _constructMethod(cls, name, self):
     return _MethodType(func, self)
 
 
-def _get_async_param(isAsync=None, **kwargs):
-    """
-    Provide a backwards-compatible way to get async param value that does not
-    cause a syntax error under Python 3.7.
-
-    @param isAsync: isAsync param value (should default to None)
-    @type isAsync: L{bool}
-
-    @param kwargs: keyword arguments of the caller (only async is allowed)
-    @type kwargs: L{dict}
-
-    @raise TypeError: Both isAsync and async specified.
-
-    @return: Final isAsync param value
-    @rtype: L{bool}
-    """
-    if "async" in kwargs:
-        warnings.warn(
-            "'async' keyword argument is deprecated, please use isAsync",
-            DeprecationWarning,
-            stacklevel=2,
-        )
-    if isAsync is None and "async" in kwargs:
-        isAsync = kwargs.pop("async")
-    if kwargs:
-        raise TypeError
-    return bool(isAsync)
-
-
 def _pypy3BlockingHack():
     """
     Work around U{https://foss.heptapod.net/pypy/pypy/-/issues/3051}
@@ -645,6 +615,5 @@ def fromFDWithoutModifyingFlags(fd, family, type, proto=None):
     "intern",
     "unichr",
     "raw_input",
-    "_get_async_param",
     "Sequence",
 ]

src/twisted/test/test_compat.py

@@ -15,7 +15,6 @@
 
 from twisted.python.compat import (
     _PYPY,
-    _get_async_param,
     bytesEnviron,
     cmp,
     comparable,
@@ -547,34 +546,3 @@ def test_alwaysBytes(self):
             types.add(type(val))
 
         self.assertEqual(list(types), [bytes])
-
-
-class GetAsyncParamTests(SynchronousTestCase):
-    """
-    Tests for L{twisted.python.compat._get_async_param}
-    """
-
-    def test_get_async_param(self):
-        """
-        L{twisted.python.compat._get_async_param} uses isAsync by default,
-        or deprecated async keyword argument if isAsync is None.
-        """
-        self.assertEqual(_get_async_param(isAsync=False), False)
-        self.assertEqual(_get_async_param(isAsync=True), True)
-        self.assertEqual(_get_async_param(isAsync=None, **{"async": False}), False)
-        self.assertEqual(_get_async_param(isAsync=None, **{"async": True}), True)
-        self.assertRaises(TypeError, _get_async_param, False, {"async": False})
-
-    def test_get_async_param_deprecation(self):
-        """
-        L{twisted.python.compat._get_async_param} raises a deprecation
-        warning if async keyword argument is passed.
-        """
-        self.assertEqual(_get_async_param(isAsync=None, **{"async": False}), False)
-        currentWarnings = self.flushWarnings(
-            offendingFunctions=[self.test_get_async_param_deprecation]
-        )
-        self.assertEqual(
-            currentWarnings[0]["message"],
-            "'async' keyword argument is deprecated, please use isAsync",
-        )