cherry-pick / pre-commit hook?

cherry-pick / pre-commit hook?

[Dave Abrahams]

Is there a good reason that git cherry-pick (without --no-commit)
doesn't run my pre-commit hook?  Is there a hook that cherry-pick
/will/ run instead?

Thanks!

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com

Re: cherry-pick / pre-commit hook?

[Jonathan Nieder]

Dave Abrahams wrote:

> Is there a good reason that git cherry-pick (without --no-commit)
> doesn't run my pre-commit hook?

Interesting question.

 $ git grep -F -e '"cherry-pick"'
 [...]
 git.c:          { "cherry-pick", cmd_cherry_pick, RUN_SETUP | NEED_WORK_TREE },
 $ git grep -F -e cmd_cherry_pick
 builtin.h:extern int cmd_cherry_pick(int argc, const char **argv, const char *prefix);
 builtin/revert.c:int cmd_cherry_pick(int argc, const char **argv, const char *prefix)
 git.c:          { "cherry-pick", cmd_cherry_pick, RUN_SETUP | NEED_WORK_TREE },

cherry-pick is implemented in builtin/revert.c.  How does it invoke
the "git commit" machinery?  Explicitly, as luck would have it.

 $ git grep --show-function -F -h -C5 -e '"commit"' -- builtin/revert.c
 static int run_git_commit(const char *defmsg)
 {
         /* 6 is max possible length of our args array including NULL */
         const char *args[6];
         int i = 0;
 
         args[i++] = "commit";
         args[i++] = "-n";
         if (signoff)
                 args[i++] = "-s";
 [...]

So cherry-pick deliberately uses -n (= --no-verify) when it calls "git commit".
Why, though?

 $ git log --oneline --follow -S'"-n"' -- builtin/revert.c
 cfd9c27 Allow cherry-pick (and revert) to add signoff line
 f810379 Make builtin-revert.c use parse_options.
 9509af6 Make git-revert & git-cherry-pick a builtin

The '-n' was copied from the old git-revert.sh script when cherry-pick
was made builtin.  Not to let the trail grow cold:

 $ git log --oneline --follow -S-n -- git-revert.sh
 9509af6 Make git-revert & git-cherry-pick a builtin
 abd6970 cherry-pick: make -r the default
 674b280 Add documentation for git-revert and git-cherry-pick.
 8bf14d6 Document the --(no-)edit switch of git-revert and git-cherry-pick
 b788498 git-revert: make --edit default.
 e2f5f6e Do not require clean tree when reverting and cherry-picking.
 9fa4db5 Do not verify reverted/cherry-picked/rebased patches.
 [...]
 $ git show -s 9fa4db5
 commit 9fa4db544e2e4d6c931f6adabc5270daec041536
 Author: Junio C Hamano <junkio@cox.net>
 Date:   Mon Aug 29 21:19:04 2005 -0700

     Do not verify reverted/cherry-picked/rebased patches.
    
     The original committer may have used validation criteria that is less
     stricter than yours.  You do not want to lose the changes even if they
     are done in substandard way from your 'commit -v' verifier's point of
     view.
    
     Signed-off-by: Junio C Hamano <junkio@cox.net>
 $

At last, an answer.  The main purpose of the pre-commit hook (and
builtin checks that preceded it) is to avoid introducing regressions
in whitespace style, encoding, and so forth; but it would make
cherry-picking unnecessarily difficult, without preventing
regressions, to apply the same standards to existing code.

> Is there a hook that cherry-pick
> /will/ run instead?

"git log --grep=pre-commit" seems to suggest that the commit-msg and
post-commit hooks will be run.  But first, what are you trying to
accomplish?  Maybe there is a simpler way, or maybe with that use
case in mind we can make changes to support it better.

Hope that helps,
Jonathan

Re: cherry-pick / pre-commit hook?

[Dave Abrahams]

Hi Jonathan,

At Wed, 8 Dec 2010 11:53:24 -0600,
Jonathan Nieder wrote:
> 
>  $ git show -s 9fa4db5
>  commit 9fa4db544e2e4d6c931f6adabc5270daec041536
>  Author: Junio C Hamano <junkio@cox.net>
>  Date:   Mon Aug 29 21:19:04 2005 -0700
> 
>      Do not verify reverted/cherry-picked/rebased patches.
>     
>      The original committer may have used validation criteria that is less
>      stricter than yours.  You do not want to lose the changes even if they
>      are done in substandard way from your 'commit -v' verifier's point of
>      view.
>     
>      Signed-off-by: Junio C Hamano <junkio@cox.net>
>  $
> 
> At last, an answer.  The main purpose of the pre-commit hook (and
> builtin checks that preceded it) is to avoid introducing regressions
> in whitespace style, encoding, and so forth; but it would make
> cherry-picking unnecessarily difficult, without preventing
> regressions, to apply the same standards to existing code.

I suspected as much.

> 
> > Is there a hook that cherry-pick
> > /will/ run instead?
> 
> "git log --grep=pre-commit" seems to suggest that the commit-msg and
> post-commit hooks will be run.  But first, what are you trying to
> accomplish?  

You're going to love this: I had sent a pull request upstream and the
maintainer of the project rejected my changes because I didn't follow
some formatting convention he didn't tell me about ;-).  So I set up a
commit hook that would prevent me from making the same mistake again,
and cherry-picked the changes one-by-one.  So it was exactly the same
scenario, except I am the author of the original changes.  

I wonder whether this would have gone better had I used rebase.

> Maybe there is a simpler way, or maybe with that use
> case in mind we can make changes to support it better.

Looking forward to hearing more.

Thanks,

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com

Re: cherry-pick / pre-commit hook?

[Jonathan Nieder]

Dave Abrahams wrote:

> You're going to love this: I had sent a pull request upstream and the
> maintainer of the project rejected my changes because I didn't follow
> some formatting convention he didn't tell me about ;-).  So I set up a
> commit hook that would prevent me from making the same mistake again,
> and cherry-picked the changes one-by-one.

Funny.  Maybe "cherry-pick --no-commit" followed by ordinary commit
would be appropriate?  That way, when the checks fail, you are in a
position to clean them up.

If the conventions were whitespace related, "git rebase --whitespace=fix"
might be even more useful.

Just for kicks, here is the cherry-pick --verify for picky
cherry-pickers.

-- 8< --
Subject: cherry-pick/revert: learn --verify to run pre-commit and commit-msg hooks

The main purpose of the pre-commit and commit-msg hooks is to avoid
introducing regressions in whitespace style, encoding, and so forth;
and it would make cherry-picking unnecessarily difficult, without
preventing regressions, to unconditionally apply the same standards to
existing code.  For this reason, in v0.99.6~51 (2005-08-29), git
learned to skip the usual hooks when cherry-picking or reverting an
existing commit.

But sometimes the checks are wanted anyway.  For example, with this
patch applied, you can safely fetch some new contributor's code:

	$ git cherry-pick -s --verify HEAD..FETCH_HEAD

while allowing the pre-commit and commit-msg hooks to run their usual
checks so the result can error out if the patches are not clean.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
Untested.  Please feel free to add some documentation and tests and
submit it for real if this looks like a good idea. :)

 builtin/revert.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/builtin/revert.c b/builtin/revert.c
index bb6e9e8..511b2ea 100644
--- a/builtin/revert.c
+++ b/builtin/revert.c
@@ -36,7 +36,7 @@ static const char * const cherry_pick_usage[] = {
 	NULL
 };
 
-static int edit, no_replay, no_commit, mainline, signoff, allow_ff;
+static int edit, no_replay, no_commit, verify, mainline, signoff, allow_ff;
 static enum { REVERT, CHERRY_PICK } action;
 static struct commit *commit;
 static int commit_argc;
@@ -67,6 +67,7 @@ static void parse_args(int argc, const char **argv)
 		OPT_INTEGER('m', "mainline", &mainline, "parent number"),
 		OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
 		OPT_STRING(0, "strategy", &strategy, "strategy", "merge strategy"),
+		OPT_BOOLEAN(0, "verify", &verify, "let hooks intervene before commiting"),
 		OPT_END(),
 		OPT_END(),
 		OPT_END(),
@@ -375,7 +376,8 @@ static int run_git_commit(const char *defmsg)
 	int i = 0;
 
 	args[i++] = "commit";
-	args[i++] = "-n";
+	if (!verify)
+		args[i++] = "-n";
 	if (signoff)
 		args[i++] = "-s";
 	if (!edit) {
-- 
1.7.2.4

Re: cherry-pick / pre-commit hook?

[Dave Abrahams]

At Wed, 8 Dec 2010 16:05:14 -0600,
Jonathan Nieder wrote:
> 
> The main purpose of the pre-commit and commit-msg hooks is to avoid
> introducing regressions in whitespace style, encoding, and so forth;
> and it would make cherry-picking unnecessarily difficult, without
> preventing regressions, to unconditionally apply the same standards to
> existing code.  For this reason, in v0.99.6~51 (2005-08-29), git
> learned to skip the usual hooks when cherry-picking or reverting an
> existing commit.
> 
> But sometimes the checks are wanted anyway.  For example, with this
> patch applied, you can safely fetch some new contributor's code:
> 
> 	$ git cherry-pick -s --verify HEAD..FETCH_HEAD
> 
> while allowing the pre-commit and commit-msg hooks to run their usual
> checks so the result can error out if the patches are not clean.
> 
> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> ---
> Untested.  Please feel free to add some documentation and tests and
> submit it for real if this looks like a good idea. :)


Well, thanks, but sadly I can only invest enough time to file this bug
report right now: if you're going to have a "pre-commit hook" concept,
but not run that hook for some kinds of commits, then that fact needs
to be documented.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com

Re: cherry-pick / pre-commit hook?

[Jonathan Nieder]

Dave Abrahams wrote:

> if you're going to have a "pre-commit hook" concept,
> but not run that hook for some kinds of commits, then that fact needs
> to be documented.

True, and thanks for a reminder.  Suggested wording?

The current githooks(5) says

 pre-commit
	This hook is invoked by git commit, and can be bypassed with
	--no-verify option.

and leaves the question of whether it is invoked by git cherry-pick
unanswered.

Re: cherry-pick / pre-commit hook?

[Junio C Hamano]

Jonathan Nieder <jrnieder@gmail.com> writes:

> Dave Abrahams wrote:
>
>> if you're going to have a "pre-commit hook" concept,
>> but not run that hook for some kinds of commits, then that fact needs
>> to be documented.
>
> True, and thanks for a reminder.  Suggested wording?
>
> The current githooks(5) says
>
>  pre-commit
> 	This hook is invoked by git commit, and can be bypassed with
> 	--no-verify option.
>
> and leaves the question of whether it is invoked by git cherry-pick
> unanswered.

Huh?  Isn't it very clear that "git commit" calls it and "git status" or
anything that is not "git commit" doesn't?

Re: cherry-pick / pre-commit hook?

[Dave Abrahams]

On Mon, Dec 27, 2010 at 11:58 AM, Junio C Hamano <gitster@pobox.com> wrote:
> Jonathan Nieder <jrnieder@gmail.com> writes:
>
>> Dave Abrahams wrote:
>>
>>> if you're going to have a "pre-commit hook" concept,
>>> but not run that hook for some kinds of commits, then that fact needs
>>> to be documented.
>>
>> True, and thanks for a reminder.  Suggested wording?
>>
>> The current githooks(5) says
>>
>>  pre-commit
>>       This hook is invoked by git commit, and can be bypassed with
>>       --no-verify option.
>>
>> and leaves the question of whether it is invoked by git cherry-pick
>> unanswered.
>
> Huh?  Isn't it very clear that "git commit" calls it and "git status" or
> anything that is not "git commit" doesn't?

Not to me.  And is it really true?  What about rebase?  What about merge?

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com

Re: cherry-pick / pre-commit hook?

[Junio C Hamano]

Jonathan Nieder <jrnieder@gmail.com> writes:

> Dave Abrahams wrote:
>
>> if you're going to have a "pre-commit hook" concept,
>> but not run that hook for some kinds of commits, then that fact needs
>> to be documented.
>
> True, and thanks for a reminder.  Suggested wording?
>
> The current githooks(5) says
>
>  pre-commit
> 	This hook is invoked by git commit, and can be bypassed with
> 	--no-verify option.
>
> and leaves the question of whether it is invoked by git cherry-pick
> unanswered.

Yeah, but do we want to answer it in this section, or in git-cherry-pick's
manual page?

After all "pre-commit" was _not_ about "before doing anything that creates
a commit", but was about "before git-commit creates a commit".  Changing
that definition is fine as long as we have a good way to explain it to the
users and more importantly a simple rule that the users can understand,
and that rule _could_ be "anything that creates a new commit".

In reality "anything that creates a new commit" cannot be that simple
rule, however.  For example, "git pull" does attempt to create a new merge
commit, but failing it because the work done by the other person you are
pulling from does not conform _your_ standard defined by your hook is not
a sane default.

I think the basic direction could be (I haven't thought things through,
just a strawman):

 - Allow --verify/--no-verify to all commands that possibly create a new
   commit, and run pre-commit hook where an updated index is about to be
   made into a commit (for some commands this may not be very easy);

 - The guideline of picking the default would probably look like this:

   (1) for existing commands, keep the current behaviour;

   (2) for a new command, --verify should be the default if the command is
       primarily about letting the user do what s/he would/could/should
       have done as "git commit" in the first place (e.g. cherry-picking
       one's own commit from a separate branch or rebasing one's own
       unpublished branch on top of updated upstream), and --no-verify
       otherwise (i.e. taking other's work and using it in a context
       different from the original).

Re: cherry-pick / pre-commit hook?

[Jakub Narebski]

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

> I think the basic direction could be (I haven't thought things through,
> just a strawman):
> 
>  - Allow --verify/--no-verify to all commands that possibly create a new
>    commit, and run pre-commit hook where an updated index is about to be
>    made into a commit (for some commands this may not be very easy);
> 
>  - The guideline of picking the default would probably look like this:
> 
>    (1) for existing commands, keep the current behaviour;
> 
>    (2) for a new command, --verify should be the default if the command is
>        primarily about letting the user do what s/he would/could/should
>        have done as "git commit" in the first place (e.g. cherry-picking
>        one's own commit from a separate branch or rebasing one's own
>        unpublished branch on top of updated upstream), and --no-verify
>        otherwise (i.e. taking other's work and using it in a context
>        different from the original).

Does it mean that for now (and perhaps also for later) it means that
"git commit" by default runs pre-commit hook, unless one use
--no-verify, and that all comands that create a new commit (rebase,
cherry-pick, revert, merge/pull) can request for pre-commit hook to be
run (if they create commit) with --verify?

I think it is a very good idea, though I don't know how difficult it
would be to make all commands that can create commit accept --verify..

-- 
Jakub Narebski
Poland
ShadeHawk on #git

Re: cherry-pick / pre-commit hook?

[Dave Abrahams]

At Tue, 28 Dec 2010 14:38:20 -0800 (PST),
Jakub Narebski wrote:
> 
> Junio C Hamano <gitster@pobox.com> writes:
> 
> > I think the basic direction could be (I haven't thought things through,
> > just a strawman):
> > 
> >  - Allow --verify/--no-verify to all commands that possibly create a new
> >    commit, and run pre-commit hook where an updated index is about to be
> >    made into a commit (for some commands this may not be very easy);
> > 
> >  - The guideline of picking the default would probably look like this:
> > 
> >    (1) for existing commands, keep the current behaviour;
> > 
> >    (2) for a new command, --verify should be the default if the command is
> >        primarily about letting the user do what s/he would/could/should
> >        have done as "git commit" in the first place (e.g. cherry-picking
> >        one's own commit from a separate branch or rebasing one's own
> >        unpublished branch on top of updated upstream), and --no-verify
> >        otherwise (i.e. taking other's work and using it in a context
> >        different from the original).
> 
> Does it mean that for now (and perhaps also for later) it means that
> "git commit" by default runs pre-commit hook, unless one use
> --no-verify, and that all comands that create a new commit (rebase,
> cherry-pick, revert, merge/pull) can request for pre-commit hook to be
> run (if they create commit) with --verify?
> 
> I think it is a very good idea

+1!

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com