[Bug fortran/99561] gfortran reports an error for a truncation that is permitted by the standard

["kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99561

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |kargl at gcc dot gnu.org

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Michal Paszta from comment #0)
> In this line of code:
> 
> INTEGER(KIND=1) :: var8 = 257_2
> 
> we try to cast an integer of kind 2 (16 bits) onto an integer of kind 1 (8
> bits, value up to 256). This will result in a truncation of the value and is
> allowed by the Fortran 2018 Standard, see Table 10.9, Fortran 2018 Standard.
> 

The sentence preceding Table 10.9 and the table tell you 
what conversions are allowed and how the conversion is
done via a built-in intrinsic subprogram.

It does tell you anything about an out-of-range value.
In fact, an INTEGER(KIND=1) entity has a range of
[-128,127], so the value of 256 is still out-of-range.

As you have found, gfortran offers a programmer a bullet
to shoot their foot (i.e, the -fno-range-check option).
On most (all?) targets supported by gfortran, you'll get 
two's complement wrap-around semantics.  You do not get
truncation, where I assume you mean that an out-of-range 
value is truncated to -128 or 127 as the situation would
merit (e.g., var8 = 257_2 <-- huge(var8) = 127).

As to the "no warning problem", you did not ask gfortran
to generate warnings.  You can use either the -Wall option
or the -Wconversion option to get a warning when using
the -fno-range-check option.

%gfcx -o z -fno-range-check -Wall a.f90
a.f90:2:33:

    2 |   integer(1), parameter :: var8 = 257_2
      |                                 1
Warning: Conversion from 'INTEGER(2)' to 'INTEGER(1)' at (1) [-Wconversion]