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From: Junio C Hamano <gitster@pobox.com>
To: Taylor Blau <me@ttaylorr.com>
Cc: Thomas Guyot-Sionnest <tguyot@gmail.com>,
	git@vger.kernel.org, dermoth@aei.ca, peff@peff.net
Subject: Re: [PATCH v2] diff: Fix modified lines stats with --stat and --numstat
Date: Sun, 20 Sep 2020 13:36:27 -0700	[thread overview]
Message-ID: <xmqqd02ggp84.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <xmqqlfh4gt5z.fsf@gitster.c.googlers.com> (Junio C. Hamano's message of "Sun, 20 Sep 2020 12:11:20 -0700")

Junio C Hamano <gitster@pobox.com> writes:

> Summarizing the above, I think the second best fix is this (which
> means that the posted patch is the third best):
>
> 	/*
> 	 * diff_fill_oid_info() marked one/two->oid with null_oid
> 	 * for a path whose oid is not available.  Disable early
> 	 * return optimization for them.
> 	 */
> 	if (oideq(&one->oid, &null_oid) || oideq(&two->oid, &null_oid))
> 		same_contents = 0; /* could be different */
> 	else if (oideq(&one->oid, &two->oid))
> 		same_contents = 1; /* definitely the same */
> 	else
> 		same_contents = 0; /* definitely different */

A tangent.

There is this code in diff.c::fill_metainfo() that is used to
populate the "index" header element of "diff --patch" output:

	if (one && two && !oideq(&one->oid, &two->oid)) {
		const unsigned hexsz = the_hash_algo->hexsz;
		int abbrev = o->abbrev ? o->abbrev : DEFAULT_ABBREV;

		if (o->flags.full_index)
			abbrev = hexsz;

		if (o->flags.binary) {
			mmfile_t mf;
			if ((!fill_mmfile(o->repo, &mf, one) &&
			     diff_filespec_is_binary(o->repo, one)) ||
			    (!fill_mmfile(o->repo, &mf, two) &&
			     diff_filespec_is_binary(o->repo, two)))
				abbrev = hexsz;
		}
		strbuf_addf(msg, "%s%sindex %s..%s", line_prefix, set,
			    diff_abbrev_oid(&one->oid, abbrev),
			    diff_abbrev_oid(&two->oid, abbrev));
		if (one->mode == two->mode)
			strbuf_addf(msg, " %06o", one->mode);
		strbuf_addf(msg, "%s\n", reset);
	}

Currently it is OK because there can only be one side that
diff_fill_oid_info() would mark as "oid unavailable" (e.g. reading
standard input stream).  If a new feature is introducing a situation
where both ends have null_oid, which was so far been impossible,
we'd probably need to factor out the condition used in the above
into a helper function, e.g.

    static int cannot_be_the_same(struct diff_filespec *one, struct diff_filespec *two)
    {
	if ((oideq(&one->oid, &null_oid) || oideq(&two->oid, &null_oid))
		return 1;
	else if (oideq(&one->oid, &two->oid))
		return 0;
	else
		return 1;
    }

and rewrite the conditional in fill_metainfo() to

	if (one && two && cannot_be_the_same(one, two)) {
		...

The "second best fix" could then become a single liner:

	same_contents = !cannot_be_the_same(one, two);

using the helper.


  parent reply	other threads:[~2020-09-20 20:36 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 11:32 Allow passing pipes to diff --no-index + bugfix Thomas Guyot-Sionnest
2020-09-18 11:32 ` [PATCH 1/2] diff: Fix modified lines stats with --stat and --numstat Thomas Guyot-Sionnest
2020-09-18 14:46   ` Taylor Blau
2020-09-18 15:10     ` Thomas Guyot-Sionnest
2020-09-18 17:37       ` Jeff King
2020-09-18 18:00         ` Thomas Guyot-Sionnest
2020-09-20  4:53       ` Thomas Guyot
2020-09-18 17:27   ` Jeff King
2020-09-18 17:52     ` Thomas Guyot-Sionnest
2020-09-18 18:06       ` Junio C Hamano
2020-09-23 19:16         ` Johannes Schindelin
2020-09-23 19:23           ` Junio C Hamano
2020-09-23 20:44             ` Johannes Schindelin
2020-09-24  4:49               ` Thomas Guyot
2020-09-24  5:24                 ` [PATCH v3] " Thomas Guyot-Sionnest
2020-09-24  7:41                   ` [PATCH v4] " Thomas Guyot-Sionnest
2020-09-24  6:40                 ` [PATCH 1/2] " Junio C Hamano
2020-09-24  7:13                   ` Thomas Guyot
2020-09-24 17:19                     ` Junio C Hamano
2020-09-24 17:38                       ` Junio C Hamano
2020-09-23 15:05     ` Johannes Schindelin
2020-09-20 13:09   ` [PATCH v2] " Thomas Guyot-Sionnest
2020-09-20 15:39     ` Taylor Blau
2020-09-20 16:38       ` Thomas Guyot
2020-09-20 19:11       ` Junio C Hamano
2020-09-20 20:08         ` Junio C Hamano
2020-09-20 20:36         ` Junio C Hamano [this message]
2020-09-20 22:15           ` Junio C Hamano
2020-09-21 19:26         ` Jeff King
2020-09-21 21:51           ` Junio C Hamano
2020-09-21 22:20             ` Jeff King
2020-09-21 22:37               ` Junio C Hamano
2020-09-18 11:32 ` [PATCH 2/2] Allow passing pipes for input pipes to diff --no-index Thomas Guyot-Sionnest
2020-09-18 14:36   ` Taylor Blau
2020-09-18 16:34     ` Thomas Guyot-Sionnest
2020-09-18 17:19       ` Jeff King
2020-09-18 17:21         ` Jeff King
2020-09-18 17:39         ` Thomas Guyot-Sionnest
2020-09-18 17:48         ` Junio C Hamano
2020-09-18 18:02           ` Jeff King
2020-09-20 12:54             ` Thomas Guyot
2020-09-21 19:31               ` Jeff King
2020-09-21 20:14                 ` Junio C Hamano
2020-09-18 17:58       ` Taylor Blau
2020-09-18 18:05         ` Jeff King
2020-09-18 17:20     ` Jeff King
2020-09-18 18:00       ` Taylor Blau
2020-09-18 21:56   ` brian m. carlson
2020-09-18 17:51 ` Allow passing pipes to diff --no-index + bugfix Junio C Hamano
2020-09-18 18:24   ` Thomas Guyot-Sionnest

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