[RFC] Support for nonzero attribute

[Miika <nykseli@protonmail.com>]

On Tuesday, June 7th, 2022 at 10:46 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> On Tue, 7 Jun 2022 at 20:44, Jonathan Wakely wrote:
>
> > On Tue, 7 Jun 2022 at 20:40, Miika via Gcc gcc@gcc.gnu.org wrote:
> >
> > > On Monday, June 6th, 2022 at 9:42 PM, Ben Boeckel ben.boeckel@kitware.com wrote:
> > >
> > > > > Based on Jakub's and Yair's comments I created a new attribute "inrange".
> > > > > Inrage takes three arguments, pos min and max.
> > > > > Pos being the argument position in the function, and min and max defines the
> > > > > range of valid integer. Both min and max are inclusive and work with enums.
> > > > > Warnings are enabled with the new flag: "-Winrange".
> > > >
> > > > Is this something that could be applied to variables or types (I've not
> > > > much experience with GCC attribute internal mechanisms, so maybe not)?
> > >
> > > I took a closer look at it and looks like it can be applied.
> > >
> > > So trying to compile this:
> > > `typedef int __attribute__((inrange(0, 100))) percentage_t; int main() { int percentage __attribute__((inrange(0, 100))) = -1; percentage_t per __attribute__((inrange(0, 100))) = -1; }`
> > >
> > > Would print out something like this:
> > >
> > > foo.c: In function 'main':
> > > foo.c:3:59: warning: inrange variable 'percentage' requires integer in rage of 0..100 [-Winrange]
> >
> > N.B. "rage" should be "range".
> >
> > From the diagnostic it's not clear to me whether this is an inclusive
> > range. Is 0 allowed? Is 100 allowed?
> >
> > Using [0,100] interval notation would imply both endpoints are valid,
> > which I think matches the semantics of your attribute. Is interval
> > notation sufficiently widely understood to use here?
>
>
> Oh, Wikipedia tells me that 0..100 already means that, as an integer interval:
> https://en.wikipedia.org/wiki/Interval_(mathematics)#Integer_intervals
>
> So maybe it's fine as-is (except for the "rage" typo).

Thanks for noticing the typo. I probably need more sleep.

And I'm open to any suggestions about the diagnostic message since I'm not sure
what's the best way to explain the error to the user.