Re: [Tinycc-devel] Variable declaration as first statement in a 'case' block gives error.

[Herman ten Brugge]

On 1/20/24 09:30, grischka wrote:
> On 19.01.2024 07:18, Herman ten Brugge via Tinycc-devel wrote:
> > I wanted to avoid an extra check for ';' because I found code like:
> >
> >      case xxx: ; }
> >
> > Instead of writing 'break;' they used ';'.
> > Without checking for ';' a warning was printed:
>
> Always same problem: we want something and do something else.
>
> Anyway, what you told tcc is to accept declarations instead of
> an expression, alternatively:
>
> -                } else {
> +                } else if (!decl(VT_JMP)) {
>                      gexpr();
>                      vpop();
>
>
> Which is what happens.  Current tcc accepts:
>
>     if (x)
>         int y;
>     else
>         int z;
>
> > So how about the next patch:
> > C23: Implement declaration after label (see attached patch)
>
>     block_after_label:
>             ...
>             if (tok != ':')
>                 decl(VT_LOCAL);
>             if (tok != '}')
>                 goto again;
>             /* we accept this, but it is a mistake */
>             tcc_warning_c(warn_all)("deprecated use of label...
>
> Yes, I'd read this as "accept declarations after a label", too.
> So it might be what you want, but is it C23?
>
> Because then, to have a declaration where it was not possible
> previously, we'd now just need to put a label in front:
>
> Not accepted
>       if (x)
>           int n;
>           for (n = 0; n < x; ++n)
>                ;
>       else ...
>
> Accepted:
>       if (x)
>           decl_please: int n;
>           for (n = 0; n < x; ++n)
>                ;
>        else ...
>
> I'd think that feels a bit strange, because the label would not
> serve any purpose other than to support the declaration.
>
> And of course, if that is C23, then people then will start to
> write this.

Thanks for this long mail.

The first patch I made was clearly not correct,
The second patch was more correct but allowed too much.
I hope the third patch is more acceptable. I now only allow
declaration after label if it is inside a '{...}'.
C23: Implement declaration after label (see attached patch)

I now see another problem between gcc and clang.
The code:

   if (x) int a;
   if (x) label: int a;

Is now accepted by clang 18.0.0(pre release)
gcc >= 13.2.1 (and now tcc) and clang 17.0.6 do not allow this.

    Herman

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