Re: [patch, fortran] PR 47359 - warnings for constant conversion

[Thomas Koenig <tkoenig at netcologne dot de>]

Hi Steve,

>> The second part catches the case when the user supplies more
>> digits than appropriate for the number.  More often than not,
>> this is a KIND error.
>>
> 
> Does the above issue warnings for
> 
>   real(knd), parameter :: pi = 3.1415926535897932384626433832795029_knd
> 
> module foomod
> 
>   interface foo
>      module procedure foo4, foo8, foo10, foo16
>   end interface foo
> 
>   contains
> 
>   subroutine foo4()
>   integer, parameter :: knd = 4
>   include 'consts.def'
>   ! do something with pi
>   end subroutine 
> end module foomod

Yes, it does, if -Wconversion-extra is specified.

> If warnings occur, then IMHO the patch cannot be committed
> in its current form.

What would be the peferred alternative?

I can make this warning conditional on a new option, let's call it
-Wconversion-constant, and have this set by default by -Wsurprising
or by -Wconversion.  The new options machinery is nice enough to
specify the option name with the warning, so it is easy for a user
to turn this particular warning off.

It would also be possible to grade this warning for really fine-grained
control:

- Introduce -Wconversion-constant, enabled by -Wconversion, to warn
  about the most common error of a constant with excess precision
  without KIND, so print *,3.1415829535 would get a warning and
  print *,3.1415926535_4 would not.

- Introduce -Wconversion-constant-extra, enabled by -Wconversion-extra,
  to warn about any excess precision regardless whether a KIND number
  is present in the constant or not.

Comments?

	Thomas