[cfe-dev] ISO C3X proposal: nonnull qualifier

[Alejandro Colomar (man-pages) via cfe-dev]

Hi Joseph,

On 11/15/21 21:18, Joseph Myers wrote:
> lvalue-to-rvalue conversion loses qualifiers, which makes any rules based
> on whether the RHS of an assignment was nonnull-qualified very
> problematic.  (The specification of restrict is exceedingly tricky and
> very unlikely to be a good basis for specifying any other feature.)

Hmm.
restrict was the closest thing to a
const-like level of safety that I could think of.
It would allow a compiler to keep track of nullness
of every pointer,
and issue appropriate diagnostics
probably better than what -fanalyzer already does.

How is restrict handling that problem of lvalue-to-rvalue already?

Can you think of any other way nonnull-ness could be passed
to nested function calls with language enforcement?

The other option would be to propose plain [[gnu::nonnull]],
which couldn't be enforced across nested function calls
(or I could't think of how yet).
Well, the simplest cases (i.e., not pointer-to-pointer)
could be detected by the compiler,
but other than that, it's impossible.
But if that's the only way,
it's better than nothing.

> 
> I don't think a manpage is a good form for proposing a language feature.
> Actual proposed normative wording for the C standard, showing all relevant
> changes to all relevant subclauses, is better.
> 

My intention is that the final PDF to be sent to the committee
will have those diffs.
But I have no clue of how to do that kind of things,
so for an initial draft to discuss on,
before even presenting it to the committee,
I think my "native" language for writing technical documents
will be easier.

Also,
I'm curious,
do you do those diffs usually by hand?
I mean, you can't diff(1) a PDF, can you? :)

Considering that C moves at a 10-years pace,
and we're late for C2X,
I have until around 2030 to learn how to do that :-)


Thanks!
and kind regards,
Alex


-- 
Alejandro Colomar
Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/