From ed69da6432f1ce63d871b643dc1672cca894794f Mon Sep 17 00:00:00 2001
From: Alex Waygood <Alex.Waygood@Gmail.com>
Date: Mon, 18 Oct 2021 16:44:43 +0100
Subject: [PATCH 1/2] bpo-39679: Add tests for classmethod and staticmethod
 singledispatchmethods

In Python 3.8 and 3.9, stacking `@functools.singledispatchmethod` on top of
`@classmethod` or `@staticmethod` caused an exception to be raised if the
method was registered using type-annotations rather than
`@method.register(int)`. This was not caught by unit tests, however, as the
tests only tested the `@method.register(int)` way of registering additional
implementations. The bug is no longer present in Python 3.10+, but
`test_functools.py` is still lacking regression tests for these cases. This
commit adds these test cases.
---
 Lib/test/test_functools.py                    | 42 +++++++++++++++++++
 .../2021-10-18-16-18-41.bpo-39679.F18qcE.rst  |  2 +
 2 files changed, 44 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Tests/2021-10-18-16-18-41.bpo-39679.F18qcE.rst

diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index fece8256a3e261..3b8379b43d56b8 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -2437,6 +2437,48 @@ def _(self, arg: str):
         self.assertEqual(a.t(''), "str")
         self.assertEqual(a.t(0.0), "base")
 
+    def test_staticmethod__type_ann_register(self):
+        class A:
+            @functools.singledispatchmethod
+            @staticmethod
+            def t(arg):
+                return arg
+            @t.register
+            @staticmethod
+            def _(arg: int):
+                return isinstance(arg, int)
+            @t.register
+            @staticmethod
+            def _(arg: str):
+                return isinstance(arg, str)
+        a = A()
+
+        self.assertTrue(A.t(0))
+        self.assertTrue(A.t(''))
+        self.assertEqual(A.t(0.0), 0.0)
+
+    def test_classmethod_type_ann_register(self):
+        class A:
+            def __init__(self, arg):
+                self.arg = arg
+
+            @functools.singledispatchmethod
+            @classmethod
+            def t(cls, arg):
+                return cls("base")
+            @t.register
+            @classmethod
+            def _(cls, arg: int):
+                return cls("int")
+            @t.register
+            @classmethod
+            def _(cls, arg: str):
+                return cls("str")
+
+        self.assertEqual(A.t(0).arg, "int")
+        self.assertEqual(A.t('').arg, "str")
+        self.assertEqual(A.t(0.0).arg, "base")
+
     def test_invalid_registrations(self):
         msg_prefix = "Invalid first argument to `register()`: "
         msg_suffix = (
diff --git a/Misc/NEWS.d/next/Tests/2021-10-18-16-18-41.bpo-39679.F18qcE.rst b/Misc/NEWS.d/next/Tests/2021-10-18-16-18-41.bpo-39679.F18qcE.rst
new file mode 100644
index 00000000000000..b0d1b686392ef8
--- /dev/null
+++ b/Misc/NEWS.d/next/Tests/2021-10-18-16-18-41.bpo-39679.F18qcE.rst
@@ -0,0 +1,2 @@
+Add more test cases for `@functools.singledispatchmethod` when combined with
+`@classmethod` or `@staticmethod`.

From 14e032c41248fa67039a6e5d909241872875c4c8 Mon Sep 17 00:00:00 2001
From: Alex Waygood <Alex.Waygood@Gmail.com>
Date: Tue, 19 Oct 2021 16:01:19 +0100
Subject: [PATCH 2/2] Correct typo

---
 Lib/test/test_functools.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 3b8379b43d56b8..bdb4ddcc60cac2 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -2437,7 +2437,7 @@ def _(self, arg: str):
         self.assertEqual(a.t(''), "str")
         self.assertEqual(a.t(0.0), "base")
 
-    def test_staticmethod__type_ann_register(self):
+    def test_staticmethod_type_ann_register(self):
         class A:
             @functools.singledispatchmethod
             @staticmethod