Flag to warning about shape/alignment-change of explicit shape arrays arguments

[Thomas Koenig]

Hi Jonatan,

> If you could write bb(3,3,na) and know that unless the actual argument is exactly of shape (3,3,na) the compiler will complain, that would give very clear and safe code.

I have worked on some of the warnings, and what you
propose is somewhere between extremely hard and
impossible to do if na is anything other than
a constant.  And I have also some experience with
bug reports about false positives when something like
that is implemented less than perfectly and put it
into -Wextra.

If you really need this particular example, you can always do

type bb_t
   real :: a(3,3)
end bb_t

and then declare an array of type bb_t with what size you need.
Access to that type will not be any less efficient than a
normal array access.

What I would sometimes like in the language is some sort of
assert statement, so a user could write

   subroutine foo(a,b)
     real, dimension(:,:), intent(inout) :: a, b
     assert(size(a,1) == size(b,2))

The code could check for that condition statically
(where possible), use the information when not debugging
and thrown an error at run-time when debugging.

Of course,

     if (size(a,1) == size(b,2)) stop "Ooops!"

has half of that particular effect, but the compile-time
part is missing (it is perfectly legal to execute a stop
statement).

Regards

	Thomas