surprising interactions: interface function can make enum value invisible

[pawosm-arm]

Following code:

program enum
  implicit none
  enum, bind(C)
    enumerator ::  SUCCESS = 0
    enumerator ::  FAILURE
  end enum

  interface
    function something()
      integer(kind(FAILURE)) :: something
    end function
  end interface

  print *, SUCCESS
  print *, FAILURE
end program enum

Can't be compiled due to an error:

F90-S-0038-Symbol, failure, has not been explicitly declared (enum.f08)
  0 inform,   0 warnings,   1 severes, 0 fatal for enum

Changing type of function in the interface (not to use enum value there) causes this program to build.
This is similar example of surprising interactions as in #367.

[nncarlson]

The interface block for something is a separate scoping unit; it inherits nothing from the surrounding scope. That includes FAILURE as well as the implicit none. Did you compile this with the "-u" flag (or whatever the flang equivalent of "no implicit typing" is)? The error you got would be consistent with "-u". However without that, the example should have compiled fine with one caveat -- but it is certainly not what you intended. FAILURE is a default real in the interface block under implicit typing rules in that scope. So its real kind is being used as an integer kind value. It's likely to be a valid integer kind, but not what was intended.

This is what you need:

interface
  function something()
    import FAILURE
    implicit none
    integer(kind(FAILURE)) :: something
  end function
end interface

If flang was giving the error without "-u" then that is a flang bug; it's apparently letting the implicit none leak into the interface block when it shouldn't

[pawosm-arm]

Hi,
I'm not building with -u flag and I forgot to mention that my first observation was that the problem goes away when I removed print *, FAILURE line which made me believe that this enum constant somehow became invisible.
Also note that gfortran builds that code without any changes.

[nncarlson]

Also note that gfortran builds that code without any changes.

which it should, however, the FAILURE in the interface block is a local real variable, and not the enum FAILURE as was surely intended.

[pawosm-arm]

How do you use -u flag with flang? It doesn't seem to be documented. Unfortunately, both -fimplicit-none and -fno-implicit-none are ignored by flang:

warning: argument unused during compilation: '-fno-implicit-none' [-Wunused-command-line-argument]

[sscalpone]

Neither -fimplicit-none nor -u is supported in flang. It's been reported as flang-compiler/clang#22.

[pawosm-arm]

Closing this ticket as contrary to gfortran, Flang compiler rejected wrong code. Such behaviour should be considered as an advantage rather than a bug.