[3.15] gh-149044: Avoid C++ warnings in PySlot_END macro (GH-158866) (#158965)

gh-149044: Avoid C++ warnings in PySlot_END macro (GH-158866)

Initialize all fields in the macro. Otherwise, g++ -Wall -Wextra
complains that some fields are not initialized
[-Werror=missing-field-initializers]:

  error: missing initializer for member ‘PySlot::sl_flags’
  error: missing initializer for member ‘PySlot::<anonymous>’
  error: missing initializer for member ‘PySlot::<anonymous>’
(cherry picked from commit ba9d96f)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: miss-islington

Include/slots.h

@@ -42,7 +42,7 @@ struct PySlot {
 #define PySlot_STATIC_DATA(NAME, VALUE) \
     {.sl_id=(NAME), .sl_flags=PySlot_STATIC, .sl_ptr=(VALUE)}
 
-#define PySlot_END {0}
+#define PySlot_END {0, 0, {0}, {_Py_NULL}}
 
 
 // Macros without designated initializers (for C++11 and below):

Misc/NEWS.d/next/C_API/2026-10-05-17-09-35.gh-issue-149044.1HUiag.rst

@@ -0,0 +1,2 @@
+Fix the :c:macro:`PySlot_END` macro for C++: initialize all members to avoid
+compiler warnings. Patch by Victor Stinner.