# [Q] Determing if a commit is reachable from the HEAD ? 12 messages from 2012-01-20 to 2012-01-24. Participants: Brian Foster, Andreas Schwab, David Brown, Junio C Hamano, Sitaram Chamarty. Thread: https://gitlist.dev/t/29408 ## Brian Foster, 2012-01-20 13:33 Subject: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <201201201433.30267.brian.foster@maxim-ic.com> URL: https://gitlist.dev/e/201201201433.30267.brian.foster%40maxim-ic.com ``` Hello, Whilst I have found answers to my question on the Web, only one seems to do exactly what I want .... x---Y---y---y---y HEAD / ...--o---o---C---o---S \ n---n---N---*---* other In a script, how can I determine commit Y is reachable from the current HEAD ? And, much more importantly for my purposes, that commit N is _not_-reachable from the current HEAD ? "A is reachable from B" meaning B is an ancestor of A (B could possibly part of a merge (not shown in the above diagram)): ✓ Commits o(all), C, S, x, y(all), and Y: YES (reachable). ✗ Commits n(all), N, and *(all): NO (not-reachable). The only readily script-able answer I've found is to use `git branch --contains=Y' and check to see if the current branch (conveniently marked `*') is/isn't included in the output. That is probably Ok, but I'm wondering if there is some "better" method (with the IMPORTANT caveat it must work with GIT 1.5.x or later ;-\ ). git-rev-list(1) may be a answer (see script below), but .... `git rev-list ^Y HEAD' lists all the y commits, which is Ok (correct for my purposes). However, `git rev-list ^N HEAD' lists commits x, Y, and y(all) on branch "other", which is not-Ok: As per above, the answer I want is "NO". Apologies if I've overlooked something totally obvious ! cheers, -blf- =====(cut here and below)=====reach02.sh===== #!/bin/bash # # x---Y---y---y---y HEAD # / # ...--o---o---C---o---S # \ # n---n---N---*---* other # : ${GIT:=git} # Allow use of different installed GIT versions. update_file() { date +"%c: $*" >>file $GIT add file && $GIT commit -m "$*" file } set -e # Terminate if problem creating diagrammed situation. rm -rf -- reachable mkdir -- reachable cd reachable $GIT version $GIT init update_file o1 update_file o2 update_file "C (o3)"; $GIT tag C update_file o4 update_file "S (o5)"; $GIT tag S $GIT checkout -b other update_file n1 update_file n2 update_file "N (n3)"; $GIT tag N update_file "*1" update_file "*2" $GIT checkout master update_file x update_file "Y (y1)"; $GIT tag Y update_file y2 update_file y3 update_file y4 declare -i wrong=0 echo "Is Y reachable from HEAD? Wanted answer: Yes." $GIT log --oneline ^Y HEAD if $GIT rev-list --quiet ^Y HEAD; then echo "rev-list: YES (wanted answer)!" else echo "rev-list: No! *** not-wanted, oops... ***" wrong=$(( wrong + 1 )) fi if $GIT branch --contains=Y | grep -q -e '^\*'; then echo "contains: YES (wanted answer)!" else echo "contains: No! *** not-wanted, oops... ***" wrong=$(( wrong + 1 )) fi echo "Is N reachable from HEAD? Wanted answer: No." $GIT log --oneline ^N HEAD if $GIT rev-list --quiet ^N HEAD; then echo "rev-list: YES? *** not-wanted, oops... ***" wrong=$(( wrong + 1 )) else echo "rev-list: No (wanted answer)!" fi if $GIT branch --contains=N | grep -q -e '^\*'; then echo "contains: YES? *** not-wanted, oops... ***" wrong=$(( wrong + 1 )) else echo "contains: No (wanted answer)!" fi exit $wrong =====(cut here and above)=====reach02.sh===== -- Brian Foster Principal MTS, Software | La Ciotat, France Maxim Integrated Products | Web: http://www.maxim-ic.com/ ``` ## Andreas Schwab, 2012-01-20 14:13 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: URL: https://gitlist.dev/e/m2ehuu8nrt.fsf%40igel.home In-Reply-To: <201201201433.30267.brian.foster@maxim-ic.com> ``` Brian Foster writes: > In a script, how can I determine commit Y is reachable > from the current HEAD ? test $(git merge-base HEAD Y) = $(git rev-parse Y) > And, much more importantly > for my purposes, that commit N is _not_-reachable from > the current HEAD ? test $(git merge-base HEAD N) != $(git rev-parse N) Andreas. -- Andreas Schwab, schwab@linux-m68k.org GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." ``` ## David Brown, 2012-01-20 18:06 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <20120120180620.GA8504@codeaurora.org> URL: https://gitlist.dev/e/20120120180620.GA8504%40codeaurora.org In-Reply-To: ``` On Fri, Jan 20, 2012 at 03:13:58PM +0100, Andreas Schwab wrote: > Brian Foster writes: > > > In a script, how can I determine commit Y is reachable > > from the current HEAD ? > > test $(git merge-base HEAD Y) = $(git rev-parse Y) Almost. It works as long as there is only one merge base. You really need to check if $(git rev-parse Y) is one of $(git merge-base --all HEAD Y) if HEAD is a named branch, you can do git name-rev --refs=refs/heads/branchname Y which will give you Y relative to branchname if it is contained within it. David -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. ``` ## Junio C Hamano, 2012-01-20 19:18 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <7v7h0mfahx.fsf@alter.siamese.dyndns.org> URL: https://gitlist.dev/e/7v7h0mfahx.fsf%40alter.siamese.dyndns.org In-Reply-To: <20120120180620.GA8504@codeaurora.org> ``` David Brown writes: > On Fri, Jan 20, 2012 at 03:13:58PM +0100, Andreas Schwab wrote: >> Brian Foster writes: >> >> > In a script, how can I determine commit Y is reachable >> > from the current HEAD ? >> >> test $(git merge-base HEAD Y) = $(git rev-parse Y) > > Almost. It works as long as there is only one merge base. You really > need to check if $(git rev-parse Y) is one of $(git merge-base --all > HEAD Y) Can you give us an example of a topology to which "merge-base --all HEAD Y" gives more than one output and Y is still reachable from HEAD? It is my understanding that merge-base computation will give only Y and nothing else when Y is reachable from HEAD. I also think this assumption is used by some of the internal code in Git, and that is why I care. ``` ## Sitaram Chamarty, 2012-01-20 22:50 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: URL: https://gitlist.dev/e/CAMK1S_gkZYpK3nrNMsnmFzi%3DtzjyEjVwOo_j4Z%3Dd0hqjdF7r_w%40mail.gmail.com In-Reply-To: <201201201433.30267.brian.foster@maxim-ic.com> ``` On Fri, Jan 20, 2012 at 7:03 PM, Brian Foster wrote: > > Hello, > >  Whilst I have found answers to my question on the Web, >  only one seems to do exactly what I want .... > >                         x---Y---y---y---y  HEAD >                        / >  ...--o---o---C---o---S >                        \ >                         n---n---N---*---*  other > >  In a script, how can I determine commit Y is reachable >  from the current HEAD ?   And, much more importantly I've been using 'git rev-list HEAD..Y'. If it produces any output, Y is not reachable from HEAD (there is something in Y that is not in HEAD). ``` ## David Brown, 2012-01-20 23:33 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <20120120233335.GA20302@codeaurora.org> URL: https://gitlist.dev/e/20120120233335.GA20302%40codeaurora.org In-Reply-To: <7v7h0mfahx.fsf@alter.siamese.dyndns.org> ``` On Fri, Jan 20, 2012 at 11:18:50AM -0800, Junio C Hamano wrote: > David Brown writes: > > > On Fri, Jan 20, 2012 at 03:13:58PM +0100, Andreas Schwab wrote: > >> Brian Foster writes: > >> > >> > In a script, how can I determine commit Y is reachable > >> > from the current HEAD ? > >> > >> test $(git merge-base HEAD Y) = $(git rev-parse Y) > > > > Almost. It works as long as there is only one merge base. You really > > need to check if $(git rev-parse Y) is one of $(git merge-base --all > > HEAD Y) > > Can you give us an example of a topology to which "merge-base --all HEAD Y" > gives more than one output and Y is still reachable from HEAD? > > It is my understanding that merge-base computation will give only Y and > nothing else when Y is reachable from HEAD. I also think this assumption > is used by some of the internal code in Git, and that is why I care. Hmm, I thought I'd convinced myself that this was possible. Now, I can't come up with a way of doing it that doesn't involve improper commits with earlier timestamps than their parents. Sorry about that, David -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. ``` ## Junio C Hamano, 2012-01-21 00:04 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <7vzkdhdiot.fsf@alter.siamese.dyndns.org> URL: https://gitlist.dev/e/7vzkdhdiot.fsf%40alter.siamese.dyndns.org In-Reply-To: <20120120233335.GA20302@codeaurora.org> ``` David Brown writes: > Hmm, I thought I'd convinced myself that this was possible. Now, I > can't come up with a way of doing it that doesn't involve improper > commits with earlier timestamps than their parents. I'd actually want to see a way to do so that *does* involve timestamp skew. ``` ## David Brown, 2012-01-21 04:58 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <20120121045803.GA29328@codeaurora.org> URL: https://gitlist.dev/e/20120121045803.GA29328%40codeaurora.org In-Reply-To: <7vzkdhdiot.fsf@alter.siamese.dyndns.org> ``` On Fri, Jan 20, 2012 at 04:04:50PM -0800, Junio C Hamano wrote: > David Brown writes: > > > Hmm, I thought I'd convinced myself that this was possible. Now, I > > can't come up with a way of doing it that doesn't involve improper > > commits with earlier timestamps than their parents. > > I'd actually want to see a way to do so that *does* involve timestamp > skew. Sorry, I guess I shouldn't tried this with a recent version of git. I can't cause this, and it looks like there's some pretty sophisticated stuff in there to deal with this. David -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. ``` ## Brian Foster, 2012-01-23 09:20 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <201201231020.04041.brian.foster@maxim-ic.com> URL: https://gitlist.dev/e/201201231020.04041.brian.foster%40maxim-ic.com In-Reply-To: ``` On Friday 20 January 2012 23:50:23 Sitaram Chamarty wrote: > On Fri, Jan 20, 2012 at 7:03 PM, Brian Foster wrote: >[ ... ] > > x---Y---y---y---y HEAD > > / > > ...--o---o---C---o---S > > \ > > n---n---N---*---* other > > > > In a script, how can I determine commit Y is reachable > > from the current HEAD ? [ ... ] > > I've been using 'git rev-list HEAD..Y'. If it produces any output, > Y is not reachable from HEAD (there is something in Y that is not > in HEAD). What's interesting about this solution, at least with GIT v1.7.6.1 (I haven't tried other versions), is ‘git rev-list HEAD..Y’ does seem to work (if there is any output, then Y is not reachable from HEAD), but ‘git rev-list --quiet HEAD..Y’ does _not_ work (it seems to always(?) exit status 0). I am probably misunderstanding ‘--quiet’, which the man page cryptically describes as “... allow the caller to test the exit status to see if a range of objects is fully connected (or not).” What is meant here by “fully connected” ? cheers! -blf- -- Brian Foster Principal MTS, Software | La Ciotat, France Maxim Integrated Products | Web: http://www.maxim-ic.com/ ``` ## Junio C Hamano, 2012-01-23 16:09 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <7vk44i9z99.fsf@alter.siamese.dyndns.org> URL: https://gitlist.dev/e/7vk44i9z99.fsf%40alter.siamese.dyndns.org In-Reply-To: <201201231020.04041.brian.foster@maxim-ic.com> ``` Brian Foster writes: > I am probably misunderstanding ‘--quiet’, which the > man page cryptically describes as “... allow the > caller to test the exit status to see if a range > of objects is fully connected (or not).” What is > meant here by “fully connected” ? If the real history looks like this: ---Y---x---HEAD i.e. the commit at HEAD says "parent x" in it, and your lacks "x" for whatever reason, Y..HEAD is not fully connected. ``` ## Brian Foster, 2012-01-24 08:16 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <201201240916.15630.brian.foster@maxim-ic.com> URL: https://gitlist.dev/e/201201240916.15630.brian.foster%40maxim-ic.com In-Reply-To: <7vk44i9z99.fsf@alter.siamese.dyndns.org> ``` On Monday 23 January 2012 17:09:38 Junio C Hamano wrote: > Brian Foster writes: > > I am probably misunderstanding ‘--quiet’, which the > > man page cryptically describes as “... allow the > > caller to test the exit status to see if a range > > of objects is fully connected (or not).” What is > > meant here by “fully connected” ? > > If the real history looks like this: > > ---Y---x---HEAD > > i.e. the commit at HEAD says "parent x" in it, and your lacks "x" > for whatever reason, Y..HEAD is not fully connected. Junio, and my _what_ lacks "x"? Sorry, it looks like you typo'ed, but I cannot decipher what you meant. cheers! -blf- -- Brian Foster Principal MTS, Software | La Ciotat, France Maxim Integrated Products | Web: http://www.maxim-ic.com/ ``` ## Brian Foster, 2012-01-24 08:56 Subject: Re: [Q] Determing if a commit is reachable from the HEAD ? Message-ID: <201201240956.15624.brian.foster@maxim-ic.com> URL: https://gitlist.dev/e/201201240956.15624.brian.foster%40maxim-ic.com In-Reply-To: <7vk44i9z99.fsf@alter.siamese.dyndns.org> ``` On Monday 23 January 2012 17:09:38 Junio C Hamano wrote: > Brian Foster writes: > > I am probably misunderstanding ‘--quiet’, which the > > man page cryptically describes as “... allow the > > caller to test the exit status to see if a range > > of objects is fully connected (or not).” What is > > meant here by “fully connected” ? > > If the real history looks like this: > > ---Y---x---HEAD > > i.e. the commit at HEAD says "parent x" in it, and your [repository] > lacks "x" for whatever reason, Y..HEAD is not fully connected. Ah, Ok. Thanks! Then YES, I misunderstood ‘--quiet’. The man page caused me to think it was functionally equivalent to ‘git rev-list STUFF >/dev/null’. cheers! -blf- -- Brian Foster Principal MTS, Software | La Ciotat, France Maxim Integrated Products | Web: http://www.maxim-ic.com/ ```