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
 170