[RFC] Support for nonzero attribute

[Miika <nykseli@protonmail.com>]

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]
    3 |         int percentage __attribute__((inrange(0, 100))) = -1;
      |                                                           ^
foo.c:4:61: warning: inrange variable 'per' requires integer in rage of 0..100 [-Winrange]
    4 |         percentage_t per __attribute__((inrange(0, 100))) = -1;
      |

Miika