--- /dev/null
+#!/bin/sh
+#
+# Copyright (c) 2006 Junio C Hamano
+#
+
+publish=next
+basebranch="$1"
+if test "$#" = 2
+then
+ topic="refs/heads/$2"
+else
+ topic=`git symbolic-ref HEAD`
+fi
+
+case "$basebranch,$topic" in
+master,refs/heads/??/*)
+ ;;
+*)
+ exit 0 ;# we do not interrupt others.
+ ;;
+esac
+
+# Now we are dealing with a topic branch being rebased
+# on top of master. Is it OK to rebase it?
+
+# Is topic fully merged to master?
+not_in_master=`git-rev-list --pretty=oneline ^master "$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".