RE: [RFC] string: Allow 2-argument strscpy()

[David Laight <David.Laight@ACULAB.COM>]

From: Pavel Machek
> Sent: 07 February 2024 17:52
> 
> > > Using sizeof(dst) is the overwhelmingly common case for strscpy().
> > > Instead of requiring this everywhere, allow a 2-argument version to be
> > > used that will use the sizeof() internally.
> >
> > Yeah, this is definitely the case. I have a ton of patches replacing
> > strncpy with strscpy [1] and many of them match the pattern of:
> > | strscpy(dest, src, sizeof(dest))
> >
> > BTW, this hack for function overloading is insane. Never really looked into
> > it before.
> 
> This hack is insane, but this is also highly confusing, please don't
> do this.

An alternative would be to convert xxx(tgt, src, 0) to
xxx(tgt, src, sizeof (tgt) - that is when the specified
length is a compile-time constant zero.

Either with:
	(__builtin_constat_p(len) && (len) == 0 ? sizeof (dst) : (len))
Or, leveraging is_constexpr() and doing (I've probably got the syntax wrong):
	__Generic(0 ? (void *)(len) : (int *)0,
		void *: len,
		int *: sizeof (dst))

That probably needs a helper:
	is_constzero(value, if_zero, if_non_zero)
to make it more generally useful.

	David

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