# Strange behaviour of git diff branch1 ... branch2 5 messages from 2012-10-26 to 2012-11-12. Participants: Aaron Schrab, Nguyen Thai Ngoc Duy, Junio C Hamano. Thread: https://gitlist.dev/t/31953 ## Aaron Schrab, 2012-10-26 21:26 Subject: Strange behaviour of git diff branch1 ... branch2 Message-ID: <20121026212650.GB2612@pug.qqx.org> URL: https://gitlist.dev/e/20121026212650.GB2612%40pug.qqx.org ``` I came across this odd question on stackoverflow: http://stackoverflow.com/q/13092854/1507392 If git diff is run with "..." as a separate argument between two commit-ish arguments causes it to produce strange output. The differences seem to be the same as if "..." was left out, but change lines begin with 4 + or - characters rather than just 1. Can anybody explain what is happening here? I don't have any reason to want to use that form myself, but I'm very curious about why it produces this odd output. Thanks. ``` ## Nguyen Thai Ngoc Duy, 2012-10-27 03:51 Subject: Re: Strange behaviour of git diff branch1 ... branch2 Message-ID: URL: https://gitlist.dev/e/CACsJy8CX4Wbf3Bqez2kcQ7NGYMkqXC8MK%2B%3DhrH4iaev%2B0ZrQ8Q%40mail.gmail.com In-Reply-To: <20121026212650.GB2612@pug.qqx.org> ``` On Sat, Oct 27, 2012 at 4:26 AM, Aaron Schrab wrote: > I came across this odd question on stackoverflow: > http://stackoverflow.com/q/13092854/1507392 > > > If git diff is run with "..." as a separate argument between two commit-ish > arguments causes it to produce strange output. The differences seem to be > the same as if "..." was left out, but change lines begin with 4 + or - > characters rather than just 1. > > Can anybody explain what is happening here? I don't have any reason to want > to use that form myself, but I'm very curious about why it produces this odd > output. I'm curious too. It shows this to me diff --cc .gitignore index a188a82,a188a82,a188a82,a188a82..d4473d8 --- a/.gitignore +++ b/.gitignore @@@@@ -2,9 -2,9 -2,9 -2,9 +2,6 @@@@@ /GIT-CFLAGS /GIT-LDFLAGS /GIT-GUI-VARS ----/GIT-PREFIX ----/GIT-SCRIPT-DEFINES ----/GIT-USER-AGENT /GIT-VERSION-FILE /bin-wrappers/ /git Notice the --cc in the first line, which is combined diff. Usually combined-diff is between two points and one parent. Though somehow git passes 4 parents down combined-diff.c:show_combined_header, as you can see in the "index" line. I think we should fix rev parsing code as it does not make sense to pass 4 identical parents this way. -- Duy ``` ## Junio C Hamano, 2012-10-27 12:33 Subject: Re: Strange behaviour of git diff branch1 ... branch2 Message-ID: <4ecbe65e-4b56-4a49-96c3-1ea8b3f0c473@email.android.com> URL: https://gitlist.dev/e/4ecbe65e-4b56-4a49-96c3-1ea8b3f0c473%40email.android.com In-Reply-To: ``` Nguyen Thai Ngoc Duy wrote: > >Notice the --cc in the first line, which is combined diff. Usually >combined-diff is between two points and one parent. Though somehow git >passes 4 parents down combined-diff.c:show_combined_header, as you can >see in the "index" line. I think we should fix rev parsing code as it >does not make sense to pass 4 identical parents this way. The two heads home from HEAD...HEAD the user has on the command line. The user is getting exactly what she asked; there is nothing to fix. ``` ## Nguyen Thai Ngoc Duy, 2012-10-27 13:32 Subject: Re: Strange behaviour of git diff branch1 ... branch2 Message-ID: URL: https://gitlist.dev/e/CACsJy8BkKRxp9AQW0M0vDSL8Mb16VGSrZ1OnQpwCrERWKVLSyA%40mail.gmail.com In-Reply-To: <4ecbe65e-4b56-4a49-96c3-1ea8b3f0c473@email.android.com> ``` On Sat, Oct 27, 2012 at 7:33 PM, Junio C Hamano wrote: > > > Nguyen Thai Ngoc Duy wrote: >> >>Notice the --cc in the first line, which is combined diff. Usually >>combined-diff is between two points and one parent. Though somehow git >>passes 4 parents down combined-diff.c:show_combined_header, as you can >>see in the "index" line. I think we should fix rev parsing code as it >>does not make sense to pass 4 identical parents this way. > > The two heads home from HEAD...HEAD the user has on the command line. > > The user is getting exactly what she asked; there is nothing to fix. Is there any use case where HEAD...HEAD (or "..." alone) is actually useful? I have re-read the git-diff man page and I don't think it explains "git diff foo ... bar" syntax (from a user's point of view, not a git guru's). We could improve the documentation if "git diff foo ... bar" is useful, or reject it with an error to avoid confusion. -- Duy ``` ## Junio C Hamano, 2012-11-12 17:46 Subject: Re: Strange behaviour of git diff branch1 ... branch2 Message-ID: <7vbof2iuic.fsf@alter.siamese.dyndns.org> URL: https://gitlist.dev/e/7vbof2iuic.fsf%40alter.siamese.dyndns.org In-Reply-To: ``` Nguyen Thai Ngoc Duy writes: > On Sat, Oct 27, 2012 at 7:33 PM, Junio C Hamano wrote: >> >> Nguyen Thai Ngoc Duy wrote: >>> >>>Notice the --cc in the first line, which is combined diff. Usually >>>combined-diff is between two points and one parent. Though somehow git >>>passes 4 parents down combined-diff.c:show_combined_header, as you can >>>see in the "index" line. I think we should fix rev parsing code as it >>>does not make sense to pass 4 identical parents this way. >> >> The two heads home from HEAD...HEAD the user has on the command line. >> >> The user is getting exactly what she asked; there is nothing to fix. > > Is there any use case where HEAD...HEAD (or "..." alone) is actually useful? That is an invalid question, implying a proposal that will introduce more confusion to the users while hurting the code. There is no use case where "cat A >>A" is actually useful, either, but it does not mean "cat A >>A" should be special cased to do something different from what it happens to do in line with the case where "cat A >>B" does. I think "diff ..." or "diff HEAD...HEAD" are the same as that example. ```