Re: [Tinycc-devel] Scoping fix

[Elijah Stone]

On Thu, 21 Jan 2021, Elijah Stone wrote:

> On Thu, 21 Jan 2021, Michael Matz wrote:
>
> > You can't declare a struct in the declaration part of the for stmt 
> > (6.8.5p3), only objects of auto and register class.
>
> Hmmm.  I think the spec is somewhat ambiguous here.
>
> *snip*

FWIW Clang and 'The New C Standard: An Economic and Cultural Commentary' 
(https://people.ece.cornell.edu/land/courses/ece4760/cbook1_1.pdf) agree 
with GCC.  But ICC, MSVC, and CompCert take the opposite view.

Another expression of the inconsistency, which I think makes it even 
clearer: under this interpretation, the first two of the following forms 
are allowed but the third is not:

// 1, ok
int i; for (i = sizeof(struct foo { int m; });;)

// 2, ok
int i = sizeof(struct foo { int m; });

// 3, not ok; why not?
for (int i = sizeof(struct foo { int m; });;)

I suspect that no one ever intended for it to be possible to declare an 
identifier inside of an expression, and now we're dealing with the 
fallout.  I don't know if there's a _good_ solution, but I think that the 
most consistent option is to allow struct declarations there.

I've written a short paper on the topic outlining the problem and a few 
potential solutions for future versions of the spec; would appreciate any 
feedback: https://elronnd.net/sl.pdf

 -E