Allow for ignoring some arguments when caching. (#12189)

* `@cached` can now take an `uncached_args` which is an iterable of names to not use in the cache key.
* Requires `@cached`, @cachedList` and `@lru_cache` to use keyword arguments for clarity.
* Asserts that keyword-only arguments in cached functions are not accepted. (I tested this briefly and I don't believe this works properly.)

tests/util/caches/test_descriptors.py

@@ -141,6 +141,84 @@ class DescriptorTestCase(unittest.TestCase):
         self.assertEqual(r, "chips")
         obj.mock.assert_not_called()
 
+    @defer.inlineCallbacks
+    def test_cache_uncached_args(self):
+        """
+        Only the arguments not named in uncached_args should matter to the cache
+
+        Note that this is identical to test_cache_num_args, but provides the
+        arguments differently.
+        """
+
+        class Cls:
+            # Note that it is important that this is not the last argument to
+            # test behaviour of skipping arguments properly.
+            @descriptors.cached(uncached_args=("arg2",))
+            def fn(self, arg1, arg2, arg3):
+                return self.mock(arg1, arg2, arg3)
+
+            def __init__(self):
+                self.mock = mock.Mock()
+
+        obj = Cls()
+        obj.mock.return_value = "fish"
+        r = yield obj.fn(1, 2, 3)
+        self.assertEqual(r, "fish")
+        obj.mock.assert_called_once_with(1, 2, 3)
+        obj.mock.reset_mock()
+
+        # a call with different params should call the mock again
+        obj.mock.return_value = "chips"
+        r = yield obj.fn(2, 3, 4)
+        self.assertEqual(r, "chips")
+        obj.mock.assert_called_once_with(2, 3, 4)
+        obj.mock.reset_mock()
+
+        # the two values should now be cached; we should be able to vary
+        # the second argument and still get the cached result.
+        r = yield obj.fn(1, 4, 3)
+        self.assertEqual(r, "fish")
+        r = yield obj.fn(2, 5, 4)
+        self.assertEqual(r, "chips")
+        obj.mock.assert_not_called()
+
+    @defer.inlineCallbacks
+    def test_cache_kwargs(self):
+        """Test that keyword arguments are treated properly"""
+
+        class Cls:
+            def __init__(self):
+                self.mock = mock.Mock()
+
+            @descriptors.cached()
+            def fn(self, arg1, kwarg1=2):
+                return self.mock(arg1, kwarg1=kwarg1)
+
+        obj = Cls()
+        obj.mock.return_value = "fish"
+        r = yield obj.fn(1, kwarg1=2)
+        self.assertEqual(r, "fish")
+        obj.mock.assert_called_once_with(1, kwarg1=2)
+        obj.mock.reset_mock()
+
+        # a call with different params should call the mock again
+        obj.mock.return_value = "chips"
+        r = yield obj.fn(1, kwarg1=3)
+        self.assertEqual(r, "chips")
+        obj.mock.assert_called_once_with(1, kwarg1=3)
+        obj.mock.reset_mock()
+
+        # the values should now be cached.
+        r = yield obj.fn(1, kwarg1=2)
+        self.assertEqual(r, "fish")
+        # We should be able to not provide kwarg1 and get the cached value back.
+        r = yield obj.fn(1)
+        self.assertEqual(r, "fish")
+        # Keyword arguments can be in any order.
+        r = yield obj.fn(kwarg1=2, arg1=1)
+        self.assertEqual(r, "fish")
+        obj.mock.assert_not_called()
+
     def test_cache_with_sync_exception(self):
         """If the wrapped function throws synchronously, things should continue to work"""
 
@@ -656,7 +734,7 @@ class CachedListDescriptorTestCase(unittest.TestCase):
             def fn(self, arg1, arg2):
                 pass
 
-            @descriptors.cachedList("fn", "args1")
+            @descriptors.cachedList(cached_method_name="fn", list_name="args1")
             async def list_fn(self, args1, arg2):
                 assert current_context().name == "c1"
                 # we want this to behave like an asynchronous function
@@ -715,7 +793,7 @@ class CachedListDescriptorTestCase(unittest.TestCase):
             def fn(self, arg1):
                 pass
 
-            @descriptors.cachedList("fn", "args1")
+            @descriptors.cachedList(cached_method_name="fn", list_name="args1")
             def list_fn(self, args1) -> "Deferred[dict]":
                 return self.mock(args1)
 
@@ -758,7 +836,7 @@ class CachedListDescriptorTestCase(unittest.TestCase):
             def fn(self, arg1, arg2):
                 pass
 
-            @descriptors.cachedList("fn", "args1")
+            @descriptors.cachedList(cached_method_name="fn", list_name="args1")
             async def list_fn(self, args1, arg2):
                 # we want this to behave like an asynchronous function
                 await run_on_reactor()