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# Copyright (c) 2006, 2008 Junio C Hamano
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# The "pre-rebase" hook is run just before "git rebase" starts doing
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# its job, and can prevent the command from running by exiting with
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# The hook is called with the following parameters:
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# $1 -- the upstream the series was forked from.
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# $2 -- the branch being rebased (or empty when rebasing the current branch).
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# This sample shows how to prevent topic branches that are already
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# merged to 'next' branch from getting rebased, because allowing it
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# would result in rebasing already published history.
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topic=`git symbolic-ref HEAD` ||
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exit 0 ;# we do not interrupt rebasing detached HEAD
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exit 0 ;# we do not interrupt others.
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# Now we are dealing with a topic branch being rebased
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# on top of master. Is it OK to rebase it?
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# Does the topic really exist?
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git show-ref -q "$topic" || {
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echo >&2 "No such branch $topic"
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# Is topic fully merged to master?
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not_in_master=`git rev-list --pretty=oneline ^master "$topic"`
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if test -z "$not_in_master"
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echo >&2 "$topic is fully merged to master; better remove it."
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exit 1 ;# we could allow it, but there is no point.
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# Is topic ever merged to next? If so you should not be rebasing it.
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only_next_1=`git rev-list ^master "^$topic" ${publish} | sort`
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only_next_2=`git rev-list ^master ${publish} | sort`
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if test "$only_next_1" = "$only_next_2"
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not_in_topic=`git rev-list "^$topic" master`
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if test -z "$not_in_topic"
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echo >&2 "$topic is already up-to-date with master"
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exit 1 ;# we could allow it, but there is no point.
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not_in_next=`git rev-list --pretty=oneline ^${publish} "$topic"`
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my $msg = "* $topic has commits already merged to public branch:\n";
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my (%not_in_next) = map {
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} split(/\n/, $ARGV[1]);
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} split(/\n/, $ARGV[2])) {
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if (!exists $not_in_next{$elem->[0]}) {
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print STDERR " $elem->[1]\n";
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' "$topic" "$not_in_next" "$not_in_master"
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This sample hook safeguards topic branches that have been
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published from being rewound.
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The workflow assumed here is:
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* Once a topic branch forks from "master", "master" is never
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merged into it again (either directly or indirectly).
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* Once a topic branch is fully cooked and merged into "master",
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it is deleted. If you need to build on top of it to correct
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earlier mistakes, a new topic branch is created by forking at
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the tip of the "master". This is not strictly necessary, but
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it makes it easier to keep your history simple.
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* Whenever you need to test or publish your changes to topic
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branches, merge them into "next" branch.
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The script, being an example, hardcodes the publish branch name
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to be "next", but it is trivial to make it configurable via
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$GIT_DIR/config mechanism.
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With this workflow, you would want to know:
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(1) ... if a topic branch has ever been merged to "next". Young
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topic branches can have stupid mistakes you would rather
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clean up before publishing, and things that have not been
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merged into other branches can be easily rebased without
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affecting other people. But once it is published, you would
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not want to rewind it.
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(2) ... if a topic branch has been fully merged to "master".
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Then you can delete it. More importantly, you should not
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build on top of it -- other people may already want to
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change things related to the topic as patches against your
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"master", so if you need further changes, it is better to
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fork the topic (perhaps with the same name) afresh from the
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Let's look at this example:
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o---o---o---o---o---o---o---o---o---o "next"
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/ / c---c---c---c B /
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---o---o---o---o---o---o---o---o---o---o---o "master"
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A, B and C are topic branches.
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* A has one fix since it was merged up to "next".
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* B has finished. It has been fully merged up to "master" and "next",
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and is ready to be deleted.
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* C has not merged to "next" at all.
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We would want to allow C to be rebased, refuse A, and encourage
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git rev-list ^master ^topic next
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git rev-list ^master next
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if these match, topic has not merged in next at all.
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git rev-list master..topic
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if this is empty, it is fully merged to "master".
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.git/hooks/pre-rebase.sample
