From: Junio C Hamano <gitster@pobox.com>
To: "Randall S. Becker" <rsbecker@nexbridge.com>
Cc: "'Barret Rhoden'" <brho@google.com>, <git@vger.kernel.org>,
"'Stefan Beller'" <stefanbeller@gmail.com>,
"'Jeff Smith'" <whydoubt@gmail.com>,
"'Jeff King'" <peff@peff.net>
Subject: Re: [PATCH] blame: add the ability to ignore commits
Date: Mon, 14 Jan 2019 22:08:17 -0800 [thread overview]
Message-ID: <xmqqd0oytpv2.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <003c01d4ac36$bdf29470$39d7bd50$@nexbridge.com> (Randall S. Becker's message of "Mon, 14 Jan 2019 13:26:56 -0500")
"Randall S. Becker" <rsbecker@nexbridge.com> writes:
> On January 14, 2019 12:46, Junio C Hamano wrote:
>> Barret Rhoden <brho@google.com> writes:
>>
>> > On 2019-01-10 at 14:29 Junio C Hamano <gitster@pobox.com> wrote:
>> >> > For instance, commit X does this:
>> >> >
>> >> > -foo(x,y);
>> >> > +foo(x,y,z);
>> >> >
>> >> > Then commit Y comes along to reformat it:
>> >> >
>> >> > -foo(x,y,z);
>> >> > +foo(x, y, z);
>> >> >
>> >> > And the history / rev-list for the file looks like:
>> >> >
>> >> > ---O---A---X---B---C---D---Y---E---F
>> >> >
>> >> > I want to ignore/skip Y and see X in the blame output.
>> >>
>> >> If you skip Y, the altered history would have "foo(x, y, z)" in E,
>> >> "foo(x,y,z)" in X, and "foo(x,y)" in A. If you start blaming from F,
>> >> you'd get E as the commit that explains the latest state. If you do
>> >> not skip Y, you'd get Y. I am not sure how you'd get X in either
>> >> case.
>> >
>> ...
>
> From my own community, this came up also. The intent was to show everyone
> who touched a particular line, throughout history, not just the current one.
> Perhaps that is what Barret is going for.
I think I now understand what is going on. In short, what Barret
wanted is way more ambitious than "blame in a hypothetical history
that lacks certain commits". There is no similiarity with existing
"-S <revs>" option that I asked about in my initial review. This is
quite a different beast (and I kind-a like it ;-).
Instead of "skipping" Y, Barret wants to pretend that the effect of
commit Y, in addition to the commit Y itself, never existed in the
history. Even when blaming back from F (where it has "foo(x, y,
z)", which is the same as E and down to Y), the algorithm wants to
pretend as if E and F had that line in "foo(x,y,z)" form, i.e.
before Y touched it, and also pretend that the user started blaming
a line in that shape.
As there is no general solution [*1*] to "how did this line looked
like before this commit", such a blame may not have a meaningful
answer. When Y added a block of text without removing anything
(i.e. "git show Y" has no line that begins with '-'), and when the
user asked to blame that block of text in F, there is no sensible
answer to the question: "what got replaced by Y in this text?", so a
blame that "ignores" Y would not be able to answer "where did these
lines come from?" question. But in some cases (e.g. when "git show
Y" has only one '-' line, immediately followed by '+' line, both
with quite a similar contents and no other change in the patch---it
is highly plausible that in such a change, the former became the
latter, like the example in Barret's message I was responding to),
we can say "this was how the line that was modified in Y looked like
before Y" and blaming while ignoring Y can have a reasonable answer.
[Footnote]
*1* Here, I use the word "solution" in the same sense as "solution
to a math equation", not in the sense to describe the steps to
derive that "solution".
next prev parent reply other threads:[~2019-01-15 6:08 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 [this message]
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
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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