bpo-44363: Get test_capi passing with address sanitizer (pythonGH-26639)

Include/Python.h

@@ -63,13 +63,22 @@
 #include "pyport.h"
 #include "pymacro.h"
 
-/* A convenient way for code to know if clang's memory sanitizer is enabled. */
+/* A convenient way for code to know if sanitizers are enabled. */
 #if defined(__has_feature)
 #  if __has_feature(memory_sanitizer)
 #    if !defined(_Py_MEMORY_SANITIZER)
 #      define _Py_MEMORY_SANITIZER
 #    endif
 #  endif
+#  if __has_feature(address_sanitizer)
+#    if !defined(_Py_ADDRESS_SANITIZER)
+#      define _Py_ADDRESS_SANITIZER
+#    endif
+#  endif
+#elif defined(__GNUC__)
+#  if defined(__SANITIZE_ADDRESS__)
+#    define _Py_ADDRESS_SANITIZER
+#  endif
 #endif
 
 #include "pymath.h"

Misc/NEWS.d/next/Tests/2021-06-10-11-19-43.bpo-44363.-K9jD0.rst

@@ -0,0 +1,2 @@
+Account for address sanitizer in test_capi. test_capi now passes when run
+GCC address sanitizer.

Modules/_testcapimodule.c

@@ -4784,6 +4784,10 @@ check_pyobject_forbidden_bytes_is_freed(PyObject *self, PyObject *Py_UNUSED(args
 static PyObject*
 check_pyobject_freed_is_freed(PyObject *self, PyObject *Py_UNUSED(args))
 {
+    /* This test would fail if run with the address sanitizer */
+#ifdef _Py_ADDRESS_SANITIZER
+    Py_RETURN_NONE;
+#else
     PyObject *op = _PyObject_CallNoArg((PyObject *)&PyBaseObject_Type);
     if (op == NULL) {
         return NULL;
@@ -4793,6 +4797,7 @@ check_pyobject_freed_is_freed(PyObject *self, PyObject *Py_UNUSED(args))
     Py_SET_REFCNT(op, 1);
     /* object memory is freed! */
     return test_pyobject_is_freed("check_pyobject_freed_is_freed", op);
+#endif
 }