Hi Ronald,

I have checked with gcc and clang on my computer (fedora 29)

This flag is defined in CLANG for the GNU and C++11 standard

See this table:

https://clang.llvm.org/docs/AttributeReference.html#deprecated

We could integrate it because the unused flag is also defined in GNU and
C++11 standard.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused

For gcc, there is this reference

https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#Common-Variable-Attributes

### CLANG
LC_ALL=C clang test.c -o test
test.c:14:13: warning: 'READONLY' is deprecated: use PY_READONLY
[-Wdeprecated-declarations]
    int i = READONLY;
            ^
test.c:8:27: note: 'READONLY' has been explicitly marked deprecated here
    READONLY __attribute((deprecated("use PY_READONLY"))) = PY_READONLY,
                          ^
1 warning generated.

LC_ALL=C clang --version test.c -o test
clang version 7.0.1 (Fedora 7.0.1-6.fc29)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

### GCC
LC_ALL=C gcc --version test.c -o test
gcc (GCC) 8.3.1 20190223 (Red Hat 8.3.1-2)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

LC_ALL=C gcc test.c -o test
test.c: In function 'main':
test.c:14:5: warning: 'READONLY' is deprecated: use PY_READONLY
[-Wdeprecated-declarations]
     int i = READONLY;
     ^~~
test.c:8:5: note: declared here
     READONLY __attribute((deprecated("use PY_READONLY"))) = PY_READONLY,
     ^~~~~~~~

But I need to know the required version of gcc and clang, in this case,
we need to know if these attributes are supported by the compiler, but
normally this is the case.

Maybe, I should ask on the python-dev mailing list.

Thank you for your advice,