Re: [RFC v5 6/7] sprintf: Add [v]sprintf_array()

[Linus Torvalds <torvalds@linux-foundation.org>]

On Thu, 10 Jul 2025 at 14:31, Alejandro Colomar <alx@kernel.org> wrote:
>
> These macros are essentially the same as the 2-argument version of
> strscpy(), but with a formatted string, and returning a pointer to the
> terminating '\0' (or NULL, on error).

No.

Stop this garbage.

You took my suggestion, and then you messed it up.

Your version of sprintf_array() is broken. It evaluates 'a' twice.
Because unlike ARRAY_SIZE(), your broken ENDOF() macro evaluates the
argument.

And you did it for no reason I can see. You said that you wanted to
return the end of the resulting string, but the fact is, not a single
user seems to care, and honestly, I think it would be wrong to care.
The size of the result is likely the more useful thing, or you could
even make these 'void' or something.

But instead you made the macro be dangerous to use.

This kind of churn is WRONG. It _looks_ like a cleanup that doesn't
change anything, but then it has subtle bugs that will come and bite
us later because you did things wrong.

I'm NAK'ing all of this. This is BAD. Cleanup patches had better be
fundamentally correct, not introduce broken "helpers" that will make
for really subtle bugs.

Maybe nobody ever ends up having that first argument with a side
effect. MAYBE. It's still very very wrong.

                Linus