Re: [PATCH] diff.c: increment buffer pointer in all code path

> On Thu, Oct 19, 2017 at 01:04:59AM -0400, Jeff King wrote:
>
>> So. That leaves me with:
>>
>>   - I'm unclear on whether next_byte() is meant to return that trailing
>>     NUL or not. I don't think it causes any bugs, but it certainly
>>     confused me for a function to take a cp/endp pair of pointers, and
>>     then dereference endp. It might be worth either fixing or clarifying
>>     with a comment.
>>
>>   - Those loops to eat trailing whitespace are doing nothing. I'm not
>>     sure if that all works out because next_byte() eats whitespaces or
>>     not (I think not, because it doesn't eat whitespace for the
>>     IGNORE_WHITESPACE_AT_EOL case). But I'm not quite sure what a test
>>     would look like.
>
> I had trouble constructing a test at first, but I think my test lines
> just weren't long enough to trigger the movement heuristics. If I switch
> to something besides seq, I can do:
>
>   # any input that has reasonably sized lines
>   look e | head -50 >file
>   git add file
>
>   perl -i -ne '
>     # pick up lines 20-25 to move to line 40, and
>     # add some trailing whitespace to them
>     if ($. >= 20 && $. <= 25) {
>       s/$/     /;
>       $hold .= $_;
>     } else {
>       print $hold if ($. == 40);
>       print;
>     }
>   ' file
>
>   git diff --color-moved --ignore-space-at-eol
>
> I think that _should_ show the block as moved, but it doesn't. But if I
> apply this patch:
>
> diff --git a/diff.c b/diff.c
> index 93dccd1817..375d9cf447 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -743,8 +743,8 @@ static int moved_entry_cmp(const struct diff_options *diffopt,
>                            const struct moved_entry *b,
>                            const void *keydata)
>  {
> -       const char *ap = a->es->line, *ae = a->es->line + a->es->len;
> -       const char *bp = b->es->line, *be = b->es->line + b->es->len;
> +       const char *ap = a->es->line, *ae = a->es->line + a->es->len - 1;
> +       const char *bp = b->es->line, *be = b->es->line + b->es->len - 1;
>
>         if (!(diffopt->xdl_opts & XDF_WHITESPACE_FLAGS))
>                 return a->es->len != b->es->len  || memcmp(ap, bp, a->es->len);
> @@ -771,7 +771,7 @@ static unsigned get_string_hash(struct emitted_diff_symbol *es, struct diff_opti
>  {
>         if (o->xdl_opts & XDF_WHITESPACE_FLAGS) {
>                 static struct strbuf sb = STRBUF_INIT;
> -               const char *ap = es->line, *ae = es->line + es->len;
> +               const char *ap = es->line, *ae = es->line + es->len - 1;
>                 int c;
>
>                 strbuf_reset(&sb);
>
> it does. It just adjusts our "end pointer" to point to the last valid
> character in the string (rather than one past),