[PATCH] pull: Allow pull to preserve merges when rebasing.

[Stephen Haberman <stephen@exigencecorp.com>]

If a user is working on master, and has merged in their feature branch, but now
has to "git pull" because master moved, with pull.rebase their feature branch
will be flattened into master.

This is because "git pull" currently does not know about rebase's preserve
merges flag, which would this behavior, and instead replay on the merge commit
of the feature branch onto the new master, and not the entire feature branch
itself.

Add a -p/--preserve-merges, to pass along git rebase if --rebase is in affect.

Also add a new pull.preserve-merges config setting, to enable this behavior as
the default.

Signed-off-by: Stephen Haberman <stephen@exigencecorp.com>
---
 git-pull.sh     | 11 +++++++++--
 t/t5520-pull.sh | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/git-pull.sh b/git-pull.sh
index f0df41c..61d1efb 100755
--- a/git-pull.sh
+++ b/git-pull.sh
@@ -40,7 +40,7 @@ test -f "$GIT_DIR/MERGE_HEAD" && die_merge
 
 strategy_args= diffstat= no_commit= squash= no_ff= ff_only=
 log_arg= verbosity= progress= recurse_submodules= verify_signatures=
-merge_args= edit=
+merge_args= edit= rebase_args=
 curr_branch=$(git symbolic-ref -q HEAD)
 curr_branch_short="${curr_branch#refs/heads/}"
 rebase=$(git config --bool branch.$curr_branch_short.rebase)
@@ -48,6 +48,10 @@ if test -z "$rebase"
 then
 	rebase=$(git config --bool pull.rebase)
 fi
+if [ $(git config --bool pull.preserve-merges) = "true" ] ;
+then
+	rebase_args=--preserve-merges
+fi
 dry_run=
 while :
 do
@@ -116,6 +120,9 @@ do
 	--no-r|--no-re|--no-reb|--no-reba|--no-rebas|--no-rebase)
 		rebase=false
 		;;
+	-p|--preserve-merges)
+		rebase_args=--preserve-merges
+		;;
 	--recurse-submodules)
 		recurse_submodules=--recurse-submodules
 		;;
@@ -292,7 +299,7 @@ fi
 merge_name=$(git fmt-merge-msg $log_arg <"$GIT_DIR/FETCH_HEAD") || exit
 case "$rebase" in
 true)
-	eval="git-rebase $diffstat $strategy_args $merge_args $verbosity"
+	eval="git-rebase $diffstat $strategy_args $merge_args $rebase_args $verbosity"
 	eval="$eval --onto $merge_head ${oldremoteref:-$merge_head}"
 	;;
 *)
diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index ed4d9c8..2a2ee97 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -148,6 +148,21 @@ test_expect_success 'branch.to-rebase.rebase should override pull.rebase' '
 	test new = $(git show HEAD:file2)
 '
 
+test_expect_success 'preserve merges' '
+	git reset --hard before-rebase &&
+	test_config pull.rebase true &&
+	test_config pull.preserve-merges true &&
+	git checkout -b keep-merge second^ &&
+	echo new > file3 &&
+	git add file3 &&
+	git commit -m "new file3" &&
+	git checkout to-rebase &&
+	git merge keep-merge &&
+	git pull . copy &&
+	test $(git rev-parse HEAD^^) = $(git rev-parse copy) &&
+	test $(git rev-parse HEAD^2) = $(git rev-parse keep-merge)
+'
+
 test_expect_success '--rebase with rebased upstream' '
 
 	git remote add -f me . &&
-- 
1.8.1.2