[Bug c++/84127] New: pragmas to disable -Wexpansion-to-defined compiler warnings seems to be broken since 7.x

[davydden at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84127

            Bug ID: 84127
           Summary: pragmas to disable -Wexpansion-to-defined compiler
                    warnings seems to be broken since 7.x
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: davydden at gmail dot com
  Target Milestone: ---

Dear all,

Looks like GCC 7.x changed in the way pragmas are processed. Below is a small
example which still produces compiler warning -Wexpansion-to-defined:

#  define DISABLE_EXTRA_DIAGNOSTICS                                     \
_Pragma("GCC diagnostic push")                                    /*!*/ \
_Pragma("GCC diagnostic ignored \"-Wexpansion-to-defined\"")            \

#  define ENABLE_EXTRA_DIAGNOSTICS                                      \
_Pragma("GCC diagnostic pop")

DISABLE_EXTRA_DIAGNOSTICS

#define BLA defined(FOO)

#if BLA
int k=0;
#endif

ENABLE_EXTRA_DIAGNOSTICS

int z = 0;


the actual pragmas used in the open-source library are here
https://github.com/dealii/dealii/blob/master/include/deal.II/base/config.h.in#L336-L374
and the discussion of this issue in the context of the library is here
https://github.com/dealii/dealii/issues/5466#issuecomment-360076509

here's a link to the same example compiled online: https://godbolt.org/g/tAv4yd 

Regards,
Denis.