Re: Fwd: Re: fmtcheck() query

[Rin Okuyama <rokuyama%rk.phys.keio.ac.jp@localhost>]

On 2017/12/13 2:41, Robert Elz wrote:
> Missing, probably not, and I didn't know about file (hadn't looked to see
> where fmtcheck() was used - though I did see the fix installed) - the case
> I am think of is one that we typically handle with an "if" and two printf
> statements, but which could be done with one with some increased flexibility.
...
> And apart from all that, I just generally prefer flexibility over rigidity
> in interfaces - lots of rope with which to hang yourself, or to produce
> something of beauty.

Thank you so much for the thorough explanation. I become to think that
the previous behavior should be reasonable.

On 2017/12/13 7:58, Christos Zoulas wrote:
> Yes, at least the new behavior made file(1) break and I am sure it is going
> to break more 3rd party software that depend on this behavior. For example
> file(1) uses fmtcheck to make sure that the formats in the description field
> match the implicit type of the file entry line. Some description lines don't
> use the values so they don't have format entries. Of course it was easy to
> fix in this case by checking that the description contains a '%' and if it
> does not, to skip the fmt_check() alltogether. Having said that, I agree
> that the new behavior should be optional and since we are going to replace
> fmt_check() with a new function that handles positional arguments we can
> also add a flag to require exact matches or not.

Yes, I'm so sorry for this breakage of file(1). It clearly indicates
possible risks of changing the behavior of fmtcheck(3).

OK, I will revert fmtcheck.c, rev 1.11. Then, I will correct the manpage
in accordance with its actual behavior.

After that, I would like to replace fmtcheck(3) with new code based on
printf_fmtmatch() by uwe. The problem is how it should be:

(1) Introduce new function like

    const char *
    fmtmatch(const char *suspect, const char *default, int flag)

to libc. We can specify whether unused args are checked or not by flag.
fmtcheck(3) uses it internally.

Alternatively,

(2) Determine the behavior by a compile-time option. fmtcheck(3) in
libc does not complain about unused args. If someone need the rigorous
check, add fmtcheck.c to SRCS with a flag like, -DFMTCHECK_UNUSED_ARGS.

For (1), everyone can choose rigorous unused args checking. However,
at the same time, we carry in another non-standard function to our
libc. I'm worried about it, although I will carefully design its
interface and post it to tech-userlevel@ for review, of course...

Thanks,
rin