On Tue, Jun 27, 2017 at 10:06 PM, Junio C Hamano <gitster@xxxxxxxxx> wrote:
> Junio C Hamano <gitster@xxxxxxxxx> writes:
>
>> Looking at the implementation of get_ws_cleaned_string() that is the
>> workhorse of emitted_symbol_cmp_no_ws(), it seems to be doing wrong
>> things for various "ignore whitespace" options (i.e. there is only
>> one implementation, while "git diff" family takes things like
>> "ignore space change", "ignore all whitespace", etc.), though.
>
> This probably deserves a bit more illustration of how I envision the
> code should evolve.
>
> In the longer term, I would prefer to see emitted_symbol_cmp_no_ws()
> to go and instead emitted_symbol_cmp() to take the diff options so
> that it can change the behaviour of the comparison function based on
> the -w/-b/--ignore-space-at-eol/etc. settings. And compare two strings
> in place.
>
> For that, you may need a helper function that takes a pointer to a
> character pointer, picks the next byte that matters while advancing
> the pointer, and returns that byte. The emitted_symbol_cmp(a, b)
> which is not used for real comparison (i.e. ordering to see if a
> sorts earlier than b) but for equivalence (i.e. considering various
> whitespace-ignoring settings, does a and b matfch?) may become
> something like:
>
> int
> emitted_symbol_eqv(struct emitted_diff_symbol *a,
> struct emitted_diff_symbol *b,
> const void *keydata) {
> struct diff_options *diffopt = keydata;
> const char *ap = a->line;
> const char *bp = b->line;
>
> while (1) {
> int ca, cb;
> ca = next_byte(&ap, diffopt);
> cb = next_byte(&bp, diffopt);
> if (ca != cb)
> return 1; /* differs */
> if (!ca)
> return 0;
> };
> }
>
> where next_byte() may look like:
>
> static int
> next_byte(const char **cp, struct diff_options *diffopt)
> {
> int retval;
>
> again:
> retval = **cp;
> if (!retval)
> return retval; /* end of string */
> if (!isspace(retval)) {
> (*cp)++; /* advance */
> return retval;
> }
>
> switch (ignore_space_type(diffopt)) {
> case NOT_IGNORING:
> (*cp)++; /* advance */
> return retval;
> case IGNORE_SPACE_CHANGE:
> while (**cp && isspace(**cp))
> (*cp)++; /* squash consecutive spaces */
> return ' '; /* normalize spaces with a SP */
> case IGNORE_ALL_SPACE:
> (*cp)++; /* advance */
> goto again;
> ... other cases here ...
> }
> }
>
>
I just rebased the diff series on top of the hashmap series and now
I want to implement the compare function based on the new data
feature. So I thought I might start off this proposal, as you seem to
have good taste for how to approach problems.
It turns out that the code here is rather a very loose proposal,
not to be copied literally, because of these constraints:
* When dealing with user content, we do not have C-strings,
but memory + length, such that next_byte also needs to be
aware of the end pointer.
* The ignore_space_type() as well as these constants do not exist
as-is, I think the cleanest for now is to parse diffopt->xdl_opts via
DIFF_XDL_TST
Thanks,
Stefan
