gh-107810: Improve DeprecationWarning for metaclasses with custom tp_new (GH-107834)

Co-authored-by: Kirill Podoprigora <kirill.bast9@mail.ru>

3 files changed, 5 insertions, 4 deletions

diff --git a/Lib/test/test_capi/test_misc.py b/Lib/test/test_capi/test_misc.py
index 001d37d..c812122 100644
--- a/Lib/test/test_capi/test_misc.py
+++ b/Lib/test/test_capi/test_misc.py
@@ -611,7 +611,7 @@ class CAPITest(unittest.TestCase):
 
         # Class creation from C
         with warnings_helper.check_warnings(
-                ('.*custom tp_new.*in Python 3.14.*', DeprecationWarning),
+                ('.* _testcapi.Subclass .* custom tp_new.*in Python 3.14.*', DeprecationWarning),
                 ):
             sub = _testcapi.make_type_with_base(Base)
         self.assertTrue(issubclass(sub, Base))
diff --git a/Misc/NEWS.d/next/C API/2023-08-10-11-12-25.gh-issue-107810.oJ40Qx.rst b/Misc/NEWS.d/next/C API/2023-08-10-11-12-25.gh-issue-107810.oJ40Qx.rst
new file mode 100644
index 0000000..c8a1f6d
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2023-08-10-11-12-25.gh-issue-107810.oJ40Qx.rst
@@ -0,0 +1 @@
+Improve :exc:`DeprecationWarning` for uses of :c:type:`PyType_Spec` with metaclasses that have custom ``tp_new``.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 71e96f5..aca14e7 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -4264,9 +4264,9 @@ _PyType_FromMetaclass_impl(
         if (_allow_tp_new) {
             if (PyErr_WarnFormat(
                     PyExc_DeprecationWarning, 1,
-                    "Using PyType_Spec with metaclasses that have custom "
-                    "tp_new is deprecated and will no longer be allowed in "
-                    "Python 3.14.") < 0) {
+                    "Type %s uses PyType_Spec with a metaclass that has custom "
+                    "tp_new. This is deprecated and will no longer be allowed in "
+                    "Python 3.14.", spec->name) < 0) {
                 goto finally;
             }
         }