Re: [PATCH] diffcore: add a filter to find a specific blob

[Stefan Beller <sbeller@google.com>]

On Thu, Dec 14, 2017 at 6:18 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Jonathan Nieder <jrnieder@gmail.com> writes:
>
>>> Regarding finding a better name, I would want to hear from others,
>>> I am happy with --find-object, though I can see --pickaxe-object
>>> or --object--filter to be a good narrative as well.
>>
>> Drat, I was hoping for an opinion.
>
> I think it would make it a better companion to --pickaxe but we need
> to align its behaviour a little bit so that it plays better with the
> "--pickaxe-all" option, and also needs to hide mode and name only
> changes just like pickaxe.

I looked into this, and the small changes needed led me to thinking
it could be integrated into the diffcore-pickaxe code completely,
roughly like (spaces mangled):

diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 9476bd2108..46f875a7b4 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -124,13 +124,21 @@ static int pickaxe_match(struct diff_filepair
*p, struct diff_options *o,
        mmfile_t mf1, mf2;
        int ret;

-       if (!o->pickaxe[0])
-               return 0;
-
        /* ignore unmerged */
        if (!DIFF_FILE_VALID(p->one) && !DIFF_FILE_VALID(p->two))
                return 0;

+       if (options->objfind) {
+               if ((DIFF_FILE_VALID(p->one) &&
+                    oidset_contains(options->objfind, &p->one->oid)) ||
+                   (DIFF_FILE_VALID(p->two) &&
+                    oidset_contains(options->objfind, &p->two->oid)))
+                       return 1;
+       }
+
+       if (!o->pickaxe[0])
+               return 0;
+
        if (o->flags.allow_textconv) {
                textconv_one = get_textconv(p->one);
                textconv_two = get_textconv(p->two);
---8<---

But then, it seems as if any pickaxe option is incompatible with
any other, i.e. from reading the code, you cannot combine -S
and -G, or even give one of them twice.

I guess that would be not a big deal for the --pickaxe-object,
but just want to point it out.

> After all, the diffcore-blobfind code was written while looking at
> the diffcore-pickaxe's code in another window shown in the pager,
> and I tend to agree with your earlier message that this is an
> extreme case of -S<contents> where the contents happens to be the
> whole file.

I disagree, as the user doesn't have the content, but the hash
over the content only and wants to know more about it. The new
option cannot be used to find a file whose partial content hashes to
the given sha1, either.

So with these considerations, I would keep the patch as currently\
queued at sb/diff-blobfind.

Thanks,
Stefan