[PATCH] Adding rebase merge strategy

[Tom Clarke <tom@u2i.com>]

In addition to adding git-merge-rebase.sh, git-merge.sh is modified
to handle the rebase strategy specially and avoids running update-ref
as rebase won't generate a merge commit. It also adds a warning
if a message is supplied when the rebase isn't used as this
will be ignored.

Signed-off-by: Tom Clarke <tom@u2i.com>
---

Incorporated comments from Johannes Schindlen.

 .gitignore                         |    1 +
 Documentation/merge-strategies.txt |    6 +++++
 Makefile                           |    2 +-
 git-merge-rebase.sh                |   17 ++++++++++++++
 git-merge.sh                       |   24 +++++++++++++++++--
 t/t3031-merge-rebase.sh            |   44 ++++++++++++++++++++++++++++++++++++
 6 files changed, 90 insertions(+), 4 deletions(-)
 create mode 100755 git-merge-rebase.sh
 create mode 100755 t/t3031-merge-rebase.sh

diff --git a/.gitignore b/.gitignore
index e0b91be..fe5cdc4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -73,6 +73,7 @@ git-merge-tree
 git-merge-octopus
 git-merge-one-file
 git-merge-ours
+git-merge-rebase
 git-merge-recursive
 git-merge-resolve
 git-merge-stupid
diff --git a/Documentation/merge-strategies.txt b/Documentation/merge-strategies.txt
index 7df0266..dff1909 100644
--- a/Documentation/merge-strategies.txt
+++ b/Documentation/merge-strategies.txt
@@ -33,3 +33,9 @@ ours::
 	merge is always the current branch head.  It is meant to
 	be used to supersede old development history of side
 	branches.
+
+rebase::
+	This rebases the current branch based on a single head.
+	Commits are rewritten as with git-rebase. This doesn't
+	produce a merge. The procedure for dealing with conflicts 
+	is the same as with git-rebase.
diff --git a/Makefile b/Makefile
index 8db4dbe..e6d3812 100644
--- a/Makefile
+++ b/Makefile
@@ -215,7 +215,7 @@ SCRIPT_SH = \
 	git-sh-setup.sh \
 	git-am.sh \
 	git-merge.sh git-merge-stupid.sh git-merge-octopus.sh \
-	git-merge-resolve.sh git-merge-ours.sh \
+	git-merge-resolve.sh git-merge-ours.sh git-merge-rebase.sh \
 	git-lost-found.sh git-quiltimport.sh git-submodule.sh \
 	git-filter-branch.sh \
 	git-stash.sh
diff --git a/git-merge-rebase.sh b/git-merge-rebase.sh
new file mode 100755
index 0000000..b75be3f
--- /dev/null
+++ b/git-merge-rebase.sh
@@ -0,0 +1,17 @@
+#!/bin/sh
+#
+# Copyright (c) 2007 Tom Clarke
+#
+# Resolve two trees with rebase
+
+# The first parameters up to -- are merge bases ignore them
+while test $1 != "--"; do shift; done
+shift
+
+# ignore the first head, it's not needed in a rebase merge
+shift
+
+# Give up if we are given two or more remotes -- not handling octopus.
+test $# = 1 || exit 2
+
+git rebase $1 || exit 2
diff --git a/git-merge.sh b/git-merge.sh
index 6c513dc..b58bee2 100755
--- a/git-merge.sh
+++ b/git-merge.sh
@@ -16,11 +16,12 @@ test -z "$(git ls-files -u)" ||
 LF='
 '
 
-all_strategies='recur recursive octopus resolve stupid ours subtree'
+all_strategies='recur recursive octopus resolve stupid ours subtree rebase'
 default_twohead_strategies='recursive'
 default_octopus_strategies='octopus'
 no_fast_forward_strategies='subtree ours'
-no_trivial_strategies='recursive recur subtree ours'
+no_trivial_strategies='recursive recur subtree ours rebase'
+no_update_ref='rebase'
 use_strategies=
 
 allow_fast_forward=t
@@ -81,11 +82,18 @@ finish () {
 			echo "No merge message -- not updating HEAD"
 			;;
 		*)
-			git update-ref -m "$rlogm" HEAD "$1" "$head" || exit 1
+			case " $wt_strategy " in
+			*" $no_update_ref "*)
+				;;
+			*)
+				git update-ref -m "$rlogm" HEAD "$1" "$head" || exit 1
+				;;
+			esac
 			;;
 		esac
 		;;
 	esac
+
 	case "$1" in
 	'')
 		;;
@@ -418,6 +426,16 @@ do
 	;;
     esac
 
+    # Check to see if there's a message in a merge type that won't produce a commit 
+    if test $have_message = "t"
+    then
+	case " $strategy " in
+	    *" $no_update_ref "*)
+	    echo >&2 "warning: Message is not used for $strategy merge strategy"
+	    ;;
+	esac
+    fi
+
     # Remember which strategy left the state in the working tree
     wt_strategy=$strategy
 
diff --git a/t/t3031-merge-rebase.sh b/t/t3031-merge-rebase.sh
new file mode 100755
index 0000000..daa03b1
--- /dev/null
+++ b/t/t3031-merge-rebase.sh
@@ -0,0 +1,44 @@
+#!/bin/sh
+
+test_description='merge-rebase backend test'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo hello >a &&
+	git add a &&
+	test_tick && git commit -m initial &&
+
+	git checkout -b branch &&
+	echo hello >b &&
+	git add b &&
+	test_tick && git commit -m onbranch &&
+
+	git checkout master &&
+	echo update >a &&
+	git add a &&
+	test_tick && git commit -m update
+'
+test_expect_success 'merging using rebase does not create merge commit' '
+	git checkout branch &&
+	git merge -s rebase master &&
+
+	( git log --pretty=oneline ) >actual &&
+	(
+		echo "4db7a5a013e67aa623d1fd294e8d46e89b3ace8f onbranch"
+		echo "893371811dbd13e85c098b72d1ab42bcfd24c2db update"
+		echo "0e960b10429bf3f1e168ee2cc7d531ac7c622580 initial"
+	) >expected &&
+	git diff -w -u expected actual
+'
+git reset --hard HEAD@{2}
+
+test_expect_success 'merging using rebase with message gives warning' '
+	git merge -m "a message" -s rebase master 2> actual &&
+	(
+		echo "warning: Message is not used for rebase merge strategy"
+	) >expected &&
+	git diff -w -u expected actual
+'
+
+test_done
-- 
1.5.3.rc7.3.g850f-dirty