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    1 #!/bin/sh
    2 #
    3 # Copyright (c) 2006, 2008 Junio C Hamano
    4 #
    5 # The "pre-rebase" hook is run just before "git rebase" starts doing
    6 # its job, and can prevent the command from running by exiting with
    7 # non-zero status.
    8 #
    9 # The hook is called with the following parameters:
   10 #
   11 # $1 -- the upstream the series was forked from.
   12 # $2 -- the branch being rebased (or empty when rebasing the current branch).
   13 #
   14 # This sample shows how to prevent topic branches that are already
   15 # merged to 'next' branch from getting rebased, because allowing it
   16 # would result in rebasing already published history.
   17 
   18 publish=next
   19 basebranch="$1"
   20 if test "$#" = 2
   21 then
   22     topic="refs/heads/$2"
   23 else
   24     topic=`git symbolic-ref HEAD` ||
   25     exit 0 ;# we do not interrupt rebasing detached HEAD
   26 fi
   27 
   28 case "$topic" in
   29 refs/heads/??/*)
   30     ;;
   31 *)
   32     exit 0 ;# we do not interrupt others.
   33     ;;
   34 esac
   35 
   36 # Now we are dealing with a topic branch being rebased
   37 # on top of master.  Is it OK to rebase it?
   38 
   39 # Does the topic really exist?
   40 git show-ref -q "$topic" || {
   41     echo >&2 "No such branch $topic"
   42     exit 1
   43 }
   44 
   45 # Is topic fully merged to master?
   46 not_in_master=`git rev-list --pretty=oneline ^master "$topic"`
   47 if test -z "$not_in_master"
   48 then
   49     echo >&2 "$topic is fully merged to master; better remove it."
   50     exit 1 ;# we could allow it, but there is no point.
   51 fi
   52 
   53 # Is topic ever merged to next?  If so you should not be rebasing it.
   54 only_next_1=`git rev-list ^master "^$topic" ${publish} | sort`
   55 only_next_2=`git rev-list ^master           ${publish} | sort`
   56 if test "$only_next_1" = "$only_next_2"
   57 then
   58     not_in_topic=`git rev-list "^$topic" master`
   59     if test -z "$not_in_topic"
   60     then
   61         echo >&2 "$topic is already up to date with master"
   62         exit 1 ;# we could allow it, but there is no point.
   63     else
   64         exit 0
   65     fi
   66 else
   67     not_in_next=`git rev-list --pretty=oneline ^${publish} "$topic"`
   68     /usr/bin/perl -e '
   69         my $topic = $ARGV[0];
   70         my $msg = "* $topic has commits already merged to public branch:\n";
   71         my (%not_in_next) = map {
   72             /^([0-9a-f]+) /;
   73             ($1 => 1);
   74         } split(/\n/, $ARGV[1]);
   75         for my $elem (map {
   76                 /^([0-9a-f]+) (.*)$/;
   77                 [$1 => $2];
   78             } split(/\n/, $ARGV[2])) {
   79             if (!exists $not_in_next{$elem->[0]}) {
   80                 if ($msg) {
   81                     print STDERR $msg;
   82                     undef $msg;
   83                 }
   84                 print STDERR " $elem->[1]\n";
   85             }
   86         }
   87     ' "$topic" "$not_in_next" "$not_in_master"
   88     exit 1
   89 fi
   90 
   91 <<\DOC_END
   92 
   93 This sample hook safeguards topic branches that have been
   94 published from being rewound.
   95 
   96 The workflow assumed here is:
   97 
   98  * Once a topic branch forks from "master", "master" is never
   99    merged into it again (either directly or indirectly).
  100 
  101  * Once a topic branch is fully cooked and merged into "master",
  102    it is deleted.  If you need to build on top of it to correct
  103    earlier mistakes, a new topic branch is created by forking at
  104    the tip of the "master".  This is not strictly necessary, but
  105    it makes it easier to keep your history simple.
  106 
  107  * Whenever you need to test or publish your changes to topic
  108    branches, merge them into "next" branch.
  109 
  110 The script, being an example, hardcodes the publish branch name
  111 to be "next", but it is trivial to make it configurable via
  112 $GIT_DIR/config mechanism.
  113 
  114 With this workflow, you would want to know:
  115 
  116 (1) ... if a topic branch has ever been merged to "next".  Young
  117     topic branches can have stupid mistakes you would rather
  118     clean up before publishing, and things that have not been
  119     merged into other branches can be easily rebased without
  120     affecting other people.  But once it is published, you would
  121     not want to rewind it.
  122 
  123 (2) ... if a topic branch has been fully merged to "master".
  124     Then you can delete it.  More importantly, you should not
  125     build on top of it -- other people may already want to
  126     change things related to the topic as patches against your
  127     "master", so if you need further changes, it is better to
  128     fork the topic (perhaps with the same name) afresh from the
  129     tip of "master".
  130 
  131 Let's look at this example:
  132 
  133            o---o---o---o---o---o---o---o---o---o "next"
  134           /       /           /           /
  135          /   a---a---b A     /           /
  136         /   /               /           /
  137            /   /   c---c---c---c B         /
  138           /   /   /             \         /
  139          /   /   /   b---b C     \       /
  140         /   /   /   /             \     /
  141     ---o---o---o---o---o---o---o---o---o---o---o "master"
  142 
  143 
  144 A, B and C are topic branches.
  145 
  146  * A has one fix since it was merged up to "next".
  147 
  148  * B has finished.  It has been fully merged up to "master" and "next",
  149    and is ready to be deleted.
  150 
  151  * C has not merged to "next" at all.
  152 
  153 We would want to allow C to be rebased, refuse A, and encourage
  154 B to be deleted.
  155 
  156 To compute (1):
  157 
  158     git rev-list ^master ^topic next
  159     git rev-list ^master        next
  160 
  161     if these match, topic has not merged in next at all.
  162 
  163 To compute (2):
  164 
  165     git rev-list master..topic
  166 
  167     if this is empty, it is fully merged to "master".
  168 
  169 DOC_END