From 4975a9eb773d0b9525315801f3e2ed3f79c432fb Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Wed, 8 Jul 2020 10:04:32 +0200
Subject: [PATCH] Revert "bpo-40170: PyType_HasFeature() now always calls
 PyType_GetFlags() (GH-19378)"

This partially reverts commit 45ec5b99aefa54552947049086e87ec01bc2fc9a.
---
 Include/object.h                                     | 12 ++++++++++--
 .../C API/2020-07-08-10-14-52.bpo-40170.N6Qx1i.rst   |  4 ++++
 2 files changed, 14 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/C API/2020-07-08-10-14-52.bpo-40170.N6Qx1i.rst

diff --git a/Include/object.h b/Include/object.h
index 537567040f9871..10f1d6a3dff2dd 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -637,8 +637,16 @@ times.
 
 
 static inline int
-PyType_HasFeature(PyTypeObject *type, unsigned long feature) {
-    return ((PyType_GetFlags(type) & feature) != 0);
+PyType_HasFeature(PyTypeObject *type, unsigned long feature)
+{
+    unsigned long flags;
+#ifdef Py_LIMITED_API
+    // PyTypeObject is opaque in the limited C API
+    flags = PyType_GetFlags(type);
+#else
+    flags = type->tp_flags;
+#endif
+    return ((flags & feature) != 0);
 }
 
 #define PyType_FastSubclass(type, flag) PyType_HasFeature(type, flag)
diff --git a/Misc/NEWS.d/next/C API/2020-07-08-10-14-52.bpo-40170.N6Qx1i.rst b/Misc/NEWS.d/next/C API/2020-07-08-10-14-52.bpo-40170.N6Qx1i.rst
new file mode 100644
index 00000000000000..760a3ff4d17b44
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2020-07-08-10-14-52.bpo-40170.N6Qx1i.rst	
@@ -0,0 +1,4 @@
+Revert :c:func:`PyType_HasFeature` change: it reads again directly the
+:c:member:`PyTypeObject.tp_flags` member when the limited C API is not used,
+rather than always calling :c:func:`PyType_GetFlags` which hides implementation
+details.