From: Barret Rhoden <brho@google.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: "René Scharfe" <l.s.r@web.de>,
git@vger.kernel.org, "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"David Kastrup" <dak@gnu.org>, "Jeff King" <peff@peff.net>,
"Jeff Smith" <whydoubt@gmail.com>,
"Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
"Stefan Beller" <stefanbeller@gmail.com>
Subject: Re: [PATCH v2 2/3] blame: add the ability to ignore commits and their changes
Date: Tue, 22 Jan 2019 14:35:00 -0500 [thread overview]
Message-ID: <20190122143500.397abc8e@gnomeregan.cam.corp.google.com> (raw)
In-Reply-To: <xmqqlg3ch85x.fsf@gitster-ct.c.googlers.com>
On 2019-01-22 at 10:14 Junio C Hamano <gitster@pobox.com> wrote:
> René Scharfe <l.s.r@web.de> writes:
>
> > Am 17.01.2019 um 21:29 schrieb Barret Rhoden:
> >> The blame_entry will get passed up the tree until we find a commit that
> >> has a diff chunk that affects those lines. If an ignored commit added
> >> more lines than it removed, the blame will fall on a commit that made a
> >> change nearby. There is no general solution here, just a best-effort
> >> approach. For a trivial example, consider ignoring this commit:
> >>
> >> Z: "Adding Lines"
> >> foo
> >> +No commit
> >> +ever touched
> >> +these lines
> >> bar
> >
> > Wouldn't it make more sense to assign such lines to unknown, perhaps
> > represented by an all-zero commit ID, instead of blaming a semi-random
> > bystander?
>
> I share the sentiment.
>
> Isn't it, however, showing a bigger problem in the "feature"?
>
> Your "a change that adds lines without removing any" is an obvious
> case where these added lines have no corresponding lines in the
> preimage, but most of the time it is unclear what line corresponds
> to what previous line. If a commit being "ignored" brought a change
> like this:
>
> 1
> -four
> -three
> +3
> +4
> 5
>
> did "+3" come from "-three"?
>
> Or did "+4" (read: "added '4'") come from "-three" (read: "removed
> 'three'")? Did it come from "-four"? Or was it genuinely added by
> that ignored commit? Your suggestion deals with the case where we
> decide that "+4" had no corresponding lines in the preimage (and
> paint it as "no blame can be assigned"). But when we decide that
> "+4" came from "-four" or "-three", we continue drilling down from
> that ignored commit and assign the blame to either the commit that
> introduced "four" or the commit that introduced "three", which would
> obviously give us different result. Worse yet, if a reader expected
> us to consider "+4" came from "-four" at that ignored commit, but
> the algorithm decided that "+4" corresponded to "-three", when we
> show the commit that eventually gets blamed for that line that has
> "4" has no "four" (it has "three"), which I suspect would confuse
> the reader of the output.
>
> So... I dunno.
I guess if you swap the lines as well as change them, then we're not
going to be able to detect that. Just to be clear, if you did this:
Commit A:
---------
other_stuff
+one
other_stuff
Commit B:
---------
other_stuff
one
+two
other_stuff
Commit C:
---------
other_stuff
-one
-two
+1
+2
other_stuff
And ignore commit C, my change will properly identify commit A and B,
e.g.:
OTHER_HASH Author Date 11) other_stuff
*A_HASH Author Date 12) 1
*B_HASH Author Date 13) 2
OTHER_HASH Author Date 14) other_stuff
But if you swapped the lines in addition to change names to numbers:
Commit C-swap:
--------------
other_stuff
-one
-two
+2
+1
other_stuff
Then it won't have the semantic knowledge that "one" == "1". If a user
is ignoring a commit, we don't have an oracle that knows exactly what
that commit did to determine what commit the user wants blamed. The
current change attempts to find the last commit that touched a line.
Barret
next prev parent reply other threads:[~2019-01-22 19:35 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-07 21:30 [PATCH] blame: add the ability to ignore commits Barret Rhoden
2019-01-07 23:13 ` Junio C Hamano
2019-01-08 16:27 ` Barret Rhoden
2019-01-08 18:26 ` Junio C Hamano
2019-01-09 20:48 ` Barret Rhoden
2019-01-10 22:29 ` Junio C Hamano
2019-01-14 15:19 ` Barret Rhoden
2019-01-14 17:45 ` Junio C Hamano
2019-01-14 18:26 ` Randall S. Becker
2019-01-14 19:03 ` Barret Rhoden
2019-01-15 6:08 ` Junio C Hamano
2019-01-09 21:21 ` Stefan Beller
2019-01-08 13:12 ` Ævar Arnfjörð Bjarmason
2019-01-08 16:41 ` Barret Rhoden
2019-01-08 18:04 ` Barret Rhoden
2019-01-17 20:29 ` [PATCH v2 0/3] " Barret Rhoden
2019-01-17 20:29 ` [PATCH v2 1/3] Move init_skiplist() outside of fsck Barret Rhoden
2019-01-18 9:25 ` Johannes Schindelin
2019-01-18 9:45 ` Ævar Arnfjörð Bjarmason
2019-01-18 17:36 ` Junio C Hamano
2019-01-18 20:59 ` Johannes Schindelin
2019-01-18 21:30 ` Jeff King
2019-01-18 22:26 ` Ævar Arnfjörð Bjarmason
2019-01-22 7:12 ` Jeff King
2019-01-22 9:46 ` Ævar Arnfjörð Bjarmason
2019-01-22 17:54 ` Junio C Hamano
2019-01-22 18:28 ` Jeff King
2019-01-17 20:29 ` [PATCH v2 2/3] blame: add the ability to ignore commits and their changes Barret Rhoden
2019-01-18 9:47 ` Johannes Schindelin
2019-01-18 17:33 ` Barret Rhoden
2019-01-20 18:19 ` René Scharfe
2019-01-22 15:26 ` Barret Rhoden
2019-01-22 18:14 ` Junio C Hamano
2019-01-22 19:35 ` Barret Rhoden [this message]
2019-01-23 19:26 ` Junio C Hamano
2019-02-01 20:37 ` Barret Rhoden
2019-01-17 20:29 ` [PATCH v2 3/3] blame: add a config option to mark ignored lines Barret Rhoden
2019-01-18 10:03 ` Johannes Schindelin
2019-01-18 9:52 ` [PATCH v2 0/3] blame: add the ability to ignore commits Ævar Arnfjörð Bjarmason
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