[PATCH] git-merge: add option --no-ff

[Lars Hjemli <hjemli@gmail.com>]

This new option forces all merges to create a "true" merge commit, i.e. a
commit with multiple parents.

Although a fast-forward would normally be The Right Thing, it isn't when the
branches to be merged originated in subversion and the merge commit will
be pushed back by means of 'git svn dcommit'. In these cases, a fast-
forward merge simply will not work.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
---
 Documentation/merge-options.txt |    4 ++++
 git-merge.sh                    |   13 +++++++++++--
 t/t6028-merge-up-to-date.sh     |   25 +++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/Documentation/merge-options.txt b/Documentation/merge-options.txt
index d64c259..ed28017 100644
--- a/Documentation/merge-options.txt
+++ b/Documentation/merge-options.txt
@@ -25,3 +25,7 @@
 	If there is no `-s` option, a built-in list of strategies
 	is used instead (`git-merge-recursive` when merging a single
 	head, `git-merge-octopus` otherwise).
+
+--no-ff::
+	Force the creation of a merge commit even when the merge would
+	have resolved as a fast-forward operation.
diff --git a/git-merge.sh b/git-merge.sh
index 3a01db0..13b98e6 100755
--- a/git-merge.sh
+++ b/git-merge.sh
@@ -3,7 +3,7 @@
 # Copyright (c) 2005 Junio C Hamano
 #
 
-USAGE='[-n] [--summary] [--no-commit] [--squash] [-s <strategy>] [-m=<merge-message>] <commit>+'
+USAGE='[-n] [--summary] [--no-commit] [--no-ff] [--squash] [-s <strategy>] [-m=<merge-message>] <commit>+'
 
 SUBDIRECTORY_OK=Yes
 . git-sh-setup
@@ -165,6 +165,10 @@ do
 		merge_msg="$1"
 		have_message=t
 		;;
+	--no-ff)
+		no_ff=t
+		no_fast_forward_strategies=$all_strategies
+		;;
 	-*)	usage ;;
 	*)	break ;;
 	esac
@@ -444,7 +448,12 @@ done
 # auto resolved the merge cleanly.
 if test '' != "$result_tree"
 then
-    parents=$(git show-branch --independent "$head" "$@" | sed -e 's/^/-p /')
+    if test $no_ff = 't'
+    then
+        parents=$(git rev-parse "$head" "$@" | sed -e 's/^/-p /')
+    else
+        parents=$(git show-branch --independent "$head" "$@" | sed -e 's/^/-p /')
+    fi
     result_commit=$(printf '%s\n' "$merge_msg" | git commit-tree $result_tree $parents) || exit
     finish "$result_commit" "Merge made by $wt_strategy."
     dropsave
diff --git a/t/t6028-merge-up-to-date.sh b/t/t6028-merge-up-to-date.sh
index f8f3e3f..afd74e2 100755
--- a/t/t6028-merge-up-to-date.sh
+++ b/t/t6028-merge-up-to-date.sh
@@ -10,12 +10,14 @@ test_expect_success setup '
 	test_tick &&
 	git commit -m initial &&
 	git tag c0 &&
+	c0=$(git rev-parse c0)
 
 	echo second >file &&
 	git add file &&
 	test_tick &&
 	git commit -m second &&
 	git tag c1 &&
+	c1=$(git rev-parse c1)
 	git branch test
 '
 
@@ -41,6 +43,16 @@ test_expect_success 'merge -s recursive fast-forward' '
 
 '
 
+test_expect_success 'merge -s recursive --no-ff' '
+
+	git reset --hard c0 &&
+	test_tick &&
+	git merge -s recursive --no-ff c1 &&
+	test $c0 = $(git rev-parse HEAD^1) &&
+	test $c1 = $(git rev-parse HEAD^2)
+
+'
+
 test_expect_success 'merge -s ours up-to-date' '
 
 	git reset --hard c1 &&
@@ -63,6 +75,19 @@ test_expect_success 'merge -s ours fast-forward' '
 
 '
 
+test_expect_success 'merge -s ours --no-ff' '
+
+	git reset --hard c0 &&
+	test_tick &&
+	git merge -s ours --no-ff c1 &&
+	expect=$(git rev-parse c0^{tree}) &&
+	current=$(git rev-parse HEAD^{tree}) &&
+	test "$expect" = "$current" &&
+	test $c0 = $(git rev-parse HEAD^1) &&
+	test $c1 = $(git rev-parse HEAD^2)
+
+'
+
 test_expect_success 'merge -s subtree up-to-date' '
 
 	git reset --hard c1 &&
-- 
1.5.3.1.92.g2f5e