#!/bin/sh

 #

 # Copyright (c) 2006, 2008 Junio C Hamano

 #

 # The "pre-rebase" hook is run just before "git-rebase" starts doing

 # its job, and can prevent the command from running by exiting with

 # non-zero status.

 #

 # The hook is called with the following parameters:

 #

 # $1 -- the upstream the series was forked from.

 # $2 -- the branch being rebased (or empty when rebasing the current branch).

 #

 # This sample shows how to prevent topic branches that are already

 # merged to 'next' branch from getting rebased, because allowing it

 # would result in rebasing already published history.

 

 publish=next

 basebranch="$1"

 if test "$#" = 2

 then

 	topic="refs/heads/$2"

 else

 	topic=`git symbolic-ref HEAD` ||

 	exit 0 ;# we do not interrupt rebasing detached HEAD

 fi

 

 case "$topic" in

 refs/heads/??/*)

 	;;

 *)

 	exit 0 ;# we do not interrupt others.

 	;;

 esac

 

 # Now we are dealing with a topic branch being rebased

 # on top of master.  Is it OK to rebase it?

 

 # Does the topic really exist?

 git show-ref -q "$topic" || {

 	echo >&2 "No such branch $topic"

 	exit 1

 }

 

 # Is topic fully merged to master?

 not_in_master=`git-rev-list --pretty=oneline ^master "$topic"`

 if test -z "$not_in_master"

 then

 	echo >&2 "$topic is fully merged to master; better remove it."

 	exit 1 ;# we could allow it, but there is no point.

 fi

 

 # Is topic ever merged to next?  If so you should not be rebasing it.

 only_next_1=`git-rev-list ^master "^$topic" ${publish} | sort`

 only_next_2=`git-rev-list ^master           ${publish} | sort`

 if test "$only_next_1" = "$only_next_2"

 then

 	not_in_topic=`git-rev-list "^$topic" master`

 	if test -z "$not_in_topic"

 	then

 		echo >&2 "$topic is already up-to-date with master"

 		exit 1 ;# we could allow it, but there is no point.

 	else

 		exit 0

 	fi

 else

 	not_in_next=`git-rev-list --pretty=oneline ^${publish} "$topic"`

 	perl -e '

 		my $topic = $ARGV[0];

 		my $msg = "* $topic has commits already merged to public branch:\n";

 		my (%not_in_next) = map {

 			/^([0-9a-f]+) /;

 			($1 => 1);

 		} split(/\n/, $ARGV[1]);

 		for my $elem (map {

 				/^([0-9a-f]+) (.*)$/;

 				[$1 => $2];

 			} split(/\n/, $ARGV[2])) {

 			if (!exists $not_in_next{$elem->[0]}) {

 				if ($msg) {

 					print STDERR $msg;

 					undef $msg;

 				}

 				print STDERR " $elem->[1]\n";

 			}

 		}

 	' "$topic" "$not_in_next" "$not_in_master"

 	exit 1

 fi

 

 exit 0

 

 ################################################################

 

 This sample hook safeguards topic branches that have been

 published from being rewound.

 

 The workflow assumed here is:

 

  * Once a topic branch forks from "master", "master" is never

    merged into it again (either directly or indirectly).

 

  * Once a topic branch is fully cooked and merged into "master",

    it is deleted.  If you need to build on top of it to correct

    earlier mistakes, a new topic branch is created by forking at

    the tip of the "master".  This is not strictly necessary, but

    it makes it easier to keep your history simple.

 

  * Whenever you need to test or publish your changes to topic

    branches, merge them into "next" branch.

 

 The script, being an example, hardcodes the publish branch name

 to be "next", but it is trivial to make it configurable via

 $GIT_DIR/config mechanism.

 

 With this workflow, you would want to know:

 

 (1) ... if a topic branch has ever been merged to "next".  Young

     topic branches can have stupid mistakes you would rather

     clean up before publishing, and things that have not been

     merged into other branches can be easily rebased without

     affecting other people.  But once it is published, you would

     not want to rewind it.

 

 (2) ... if a topic branch has been fully merged to "master".

     Then you can delete it.  More importantly, you should not

     build on top of it -- other people may already want to

     change things related to the topic as patches against your

     "master", so if you need further changes, it is better to

     fork the topic (perhaps with the same name) afresh from the

     tip of "master".

 

 Let's look at this example:

 

 		   o---o---o---o---o---o---o---o---o---o "next"

 		  /       /           /           /

 		 /   a---a---b A     /           /

 		/   /               /           /

 	       /   /   c---c---c---c B         /

 	      /   /   /             \         /

 	     /   /   /   b---b C     \       /

 	    /   /   /   /             \     /

     ---o---o---o---o---o---o---o---o---o---o---o "master"

 

 

 A, B and C are topic branches.

 

  * A has one fix since it was merged up to "next".

 

  * B has finished.  It has been fully merged up to "master" and "next",

    and is ready to be deleted.

 

  * C has not merged to "next" at all.

 

 We would want to allow C to be rebased, refuse A, and encourage

 B to be deleted.

 

 To compute (1):

 

 	git-rev-list ^master ^topic next

 	git-rev-list ^master        next

 

 	if these match, topic has not merged in next at all.

 

 To compute (2):

 

 	git-rev-list master..topic

 

 	if this is empty, it is fully merged to "master".