Hi Junio,
On Mon, 12 Oct 2020, Junio C Hamano wrote:
> Johannes Schindelin <Johannes.Schindelin@xxxxxx> writes:
>
> > Hi Michał,
> >
> > On Mon, 12 Oct 2020, Michał Kępień wrote:
> >
> >> @@ -5203,6 +5207,22 @@ static int diff_opt_patience(const struct option *opt,
> >> return 0;
> >> }
> >>
> >> +static int diff_opt_ignore_regex(const struct option *opt,
> >> + const char *arg, int unset)
> >> +{
> >> + struct diff_options *options = opt->value;
> >> + regex_t *regex;
> >> +
> >> + BUG_ON_OPT_NEG(unset);
> >> + regex = xcalloc(1, sizeof(*regex));
> >> + if (regcomp(regex, arg, REG_EXTENDED | REG_NEWLINE))
> >> + die("invalid regex: %s", arg);
> >> + ALLOC_GROW(options->ignore_regex, options->ignore_regex_nr + 1,
> >> + options->ignore_regex_alloc);
> >> + options->ignore_regex[options->ignore_regex_nr++] = regex;
> >
> > A slightly more elegant way would be to have `ignore_regex` have the type
> > `regex_t *` and use `ALLOC_GROW_BY()` (which zeroes the newly-added
> > elements automagically).
>
> It may be "elegant", but we we know if it is "correct" on
> everybody's implementation of regex_t?
>
> A struct like
>
> struct foo {
> char *str;
> char in_place_buffer[10];
> };
>
> where str points at in_place_buffer[] only when it needs to point at
> a very short string, and points at an allocated memory on heap, can
> not be safely copied and used, and an array of such a struct breaks
> when ALLOC_GROW_BY() needs to call realloc(). Keeping an array of
> pointers to regex_t and growing it would not break even for such a
> structure type.
>
> Since we cannot rely on the implementation detail of regex_t on a
> single platform, I'd rather not to see anybody suggest such an
> "elegant" approach.
True, such an implementation detail is totally conceivable.
Thanks for the sanity check.
Having said that, my suggestion to use `ALLOC_GROW_BY()` was triggered by
the use of `xcalloc()`, and now that I think further about it, an
`xmalloc()` should be plenty enough: `regcomp()` does not need that struct
to be initialized to all zero.
Ciao,
Dscho
