[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 avoid this behavior, as it would instead replay just
the merge commit of the feature branch onto the new master, and not replay each
individual commit in the feature branch.

Add a --rebase=preserve option, which will pass along --preserve-merges to
rebase.

Also add 'preserve' to the allowed values for the pull.rebase config setting.

Signed-off-by: Stephen Haberman <stephen@exigencecorp.com>
---
Hi,

This is v3 of my previous pull.rebase=preserve patch, previously discussed here:

http://thread.gmane.org/gmane.comp.version-control.git/232061
http://thread.gmane.org/gmane.comp.version-control.git/231909

In this version, I addressed all of Eric's excellent feedback.

I believe the patch is much better now, but would still appreciate more
detailed feedback. In particular, I kind of made up how to handle and
invalid "--rebase=invalid" value, and the resulting error message.

Also, I changed git-pull's usage to include the -r parameter...not
sure if that's okay or not. Let me know if not.

Thanks!

 Documentation/config.txt   |  8 +++++
 Documentation/git-pull.txt | 18 +++++++----
 git-pull.sh                | 42 ++++++++++++++++++++----
 t/t5520-pull.sh            | 81 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 137 insertions(+), 12 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index ec57a15..4c22be2 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -766,6 +766,10 @@ branch.<name>.rebase::
 	"git pull" is run. See "pull.rebase" for doing this in a non
 	branch-specific manner.
 +
+	When preserve, also pass `--preserve-merges` along to 'git rebase'
+	so that locally committed merge commits will not be flattened
+	by running 'git pull'.
++
 *NOTE*: this is a possibly dangerous operation; do *not* use
 it unless you understand the implications (see linkgit:git-rebase[1]
 for details).
@@ -1826,6 +1830,10 @@ pull.rebase::
 	pull" is run. See "branch.<name>.rebase" for setting this on a
 	per-branch basis.
 +
+	When preserve, also pass `--preserve-merges` along to 'git rebase'
+	so that locally committed merge commits will not be flattened
+	by running 'git pull'.
++
 *NOTE*: this is a possibly dangerous operation; do *not* use
 it unless you understand the implications (see linkgit:git-rebase[1]
 for details).
diff --git a/Documentation/git-pull.txt b/Documentation/git-pull.txt
index 6ef8d59..beea10b 100644
--- a/Documentation/git-pull.txt
+++ b/Documentation/git-pull.txt
@@ -102,12 +102,18 @@ include::merge-options.txt[]
 :git-pull: 1
 
 -r::
---rebase::
-	Rebase the current branch on top of the upstream branch after
-	fetching.  If there is a remote-tracking branch corresponding to
-	the upstream branch and the upstream branch was rebased since last
-	fetched, the rebase uses that information to avoid rebasing
-	non-local changes.
+--rebase[=false|true|preserve]::
+	When true, rebase the current branch on top of the upstream
+	branch after fetching. If there is a remote-tracking branch
+	corresponding to the upstream branch and the upstream branch
+	was rebased since last fetched, the rebase uses that information
+	to avoid rebasing non-local changes.
++
+When preserve, also rebase the current branch on top of the upstream
+branch, but pass `--preserve-merges` along to `git rebase` so that
+locally created merge commits will not be flattened.
++
+When false, merge the current branch into the upstream branch.
 +
 See `pull.rebase`, `branch.<name>.rebase` and `branch.autosetuprebase` in
 linkgit:git-config[1] if you want to make `git pull` always use
diff --git a/git-pull.sh b/git-pull.sh
index f0df41c..78ad52d 100755
--- a/git-pull.sh
+++ b/git-pull.sh
@@ -4,7 +4,7 @@
 #
 # Fetch one or more remote refs and merge it/them into the current HEAD.
 
-USAGE='[-n | --no-stat] [--[no-]commit] [--[no-]squash] [--[no-]ff] [-s strategy]... [<fetch-options>] <repo> <head>...'
+USAGE='[-n | --no-stat] [--[no-]commit] [--[no-]squash] [--[no-]ff] [-r [true|false|preserve]] [-s strategy]... [<fetch-options>] <repo> <head>...'
 LONG_USAGE='Fetch one or more remote refs and integrate it/them with the current HEAD.'
 SUBDIRECTORY_OK=Yes
 OPTIONS_SPEC=
@@ -40,13 +40,13 @@ 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)
+rebase=$(git config branch.$curr_branch_short.rebase)
 if test -z "$rebase"
 then
-	rebase=$(git config --bool pull.rebase)
+	rebase=$(git config pull.rebase)
 fi
 dry_run=
 while :
@@ -110,8 +110,27 @@ do
 		esac
 		merge_args="$merge_args$xx "
 		;;
+	-r=*|--r=*|--re=*|--reb=*|--reba=*|--rebas=*|--rebase=*|\
 	-r|--r|--re|--reb|--reba|--rebas|--rebase)
-		rebase=true
+		case "$#,$1" in
+		*,*=*)
+			rebase="${1#*=}"
+			;;
+		1,*)
+			rebase=true
+			;;
+		*)
+			# if the user typed 'git pull -r . copy', don't treat '.'
+			# as an argument to -r
+			if test true = "$2" || test false = "$2" || test preserve = "$3"
+			then
+				rebase="$2"
+				shift
+			else
+				rebase=true
+			fi
+			;;
+		esac
 		;;
 	--no-r|--no-re|--no-reb|--no-reba|--no-rebas|--no-rebase)
 		rebase=false
@@ -145,6 +164,17 @@ do
 	shift
 done
 
+if test preserve = "$rebase"
+then
+	rebase=true
+	rebase_args=--preserve-merges
+elif test ! -z "$rebase" && test false != "$rebase" && test true != "$rebase"
+then
+	echo "Invalid value for --rebase, should be true, false, or preserve"
+	usage
+	exit 1
+fi
+
 error_on_no_merge_candidates () {
 	exec >&2
 	for opt
@@ -292,7 +322,7 @@ 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..8be0482 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -148,6 +148,87 @@ test_expect_success 'branch.to-rebase.rebase should override pull.rebase' '
 	test new = $(git show HEAD:file2)
 '
 
+# add a feature branch, keep-merge, that is merged into master, so the
+# test can try preserving the merge commit (or not) with various
+# --rebase flags/pull.rebase settings.
+test_expect_success 'preserve merge setup' '
+	git reset --hard before-rebase &&
+	git checkout -b keep-merge second^ &&
+	test_commit file3 &&
+	git checkout to-rebase &&
+	git merge keep-merge &&
+	git tag before-preserve-rebase
+'
+
+test_expect_success 'pull.rebase=false create a new merge commit' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase false &&
+	git pull . copy &&
+	test $(git rev-parse HEAD^1) = $(git rev-parse before-preserve-rebase) &&
+	test $(git rev-parse HEAD^2) = $(git rev-parse copy) &&
+	test file3 = $(git show HEAD:file3.t)
+'
+
+test_expect_success 'pull.rebase=true flattens keep-merge' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase true &&
+	git pull . copy &&
+	test $(git rev-parse HEAD^^) = $(git rev-parse copy) &&
+	test file3 = $(git show HEAD:file3.t)
+'
+
+test_expect_success 'pull.rebase=preserve rebases and merges keep-merge' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase preserve &&
+	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 'pull.rebase=invalid fails' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase invalid &&
+	! git pull . copy
+'
+
+test_expect_success '--rebase=false create a new merge commit' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase true &&
+	git pull --rebase=false . copy &&
+	test $(git rev-parse HEAD^1) = $(git rev-parse before-preserve-rebase) &&
+	test $(git rev-parse HEAD^2) = $(git rev-parse copy) &&
+	test file3 = $(git show HEAD:file3.t)
+'
+
+test_expect_success '--rebase=true rebases and flattens keep-merge' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase preserve &&
+	git pull --rebase=true . copy &&
+	test $(git rev-parse HEAD^^) = $(git rev-parse copy) &&
+	test file3 = $(git show HEAD:file3.t)
+'
+
+test_expect_success '--rebase=preserve rebases and merges keep-merge' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase true &&
+	git pull --rebase=preserve . 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=invalid fails' '
+	git reset --hard before-preserve-rebase &&
+	! git pull --rebase=invalid . copy
+'
+
+test_expect_success '--rebase overrides pull.rebase=preserve and flattens keep-merge' '
+	git reset --hard before-preserve-rebase &&
+	test_config pull.rebase preserve &&
+	git pull --rebase . copy &&
+	test $(git rev-parse HEAD^^) = $(git rev-parse copy) &&
+	test file3 = $(git show HEAD:file3.t)
+'
+
 test_expect_success '--rebase with rebased upstream' '
 
 	git remote add -f me . &&
-- 
1.8.1.2