rebase: support -X to pass through strategy options

git-rebase calls out to merge strategies, but did not support merge
strategy options so far.  Add this, in the same style used in
git-merge.

Sadly we have to do the full quoting/eval dance here, since
merge-recursive supports the --subtree=<path> option which potentially
contains whitespace.

This patch does not cover git rebase -i, which does not call any merge
strategy directly except in --preserve-merges, and even then only for
merges.

[jc: with a trivial fix-up for 'expr']

Signed-off-by: Mike Lundy <mike@fluffypenguin.org>
Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -250,6 +250,13 @@ on top of the <upstream> branch using the given strategy, using
 the 'ours' strategy simply discards all patches from the <branch>,
 which makes little sense.
 
+-X <strategy-option>::
+--strategy-option=<strategy-option>::
+	Pass the <strategy-option> through to the merge strategy.
+	This implies `\--merge` and, if no strategy has been
+	specified, `-s recursive`.  Note the reversal of 'ours' and
+	'theirs' as noted in above for the `-m` option.
+
 -q::
 --quiet::
 	Be quiet. Implies --no-stat.

git-rebase.sh

@@ -44,6 +44,7 @@ To restore the original branch and stop rebasing run \"git rebase --abort\".
 "
 unset newbase
 strategy=recursive
+strategy_opts=
 do_merge=
 dotest="$GIT_DIR"/rebase-merge
 prec=4
@@ -112,7 +113,7 @@ call_merge () {
 	then
 		export GIT_MERGE_VERBOSITY=1
 	fi
-	git-merge-$strategy "$cmt^" -- "$hd" "$cmt"
+	eval 'git-merge-$strategy' $strategy_opts '"$cmt^" -- "$hd" "$cmt"'
 	rv=$?
 	case "$rv" in
 	0)
@@ -293,6 +294,27 @@ do
 	-M|-m|--m|--me|--mer|--merg|--merge)
 		do_merge=t
 		;;
+	-X*|--strategy-option*)
+		case "$#,$1" in
+		1,-X|1,--strategy-option)
+			usage ;;
+		*,-X|*,--strategy-option)
+			newopt="$2"
+			shift ;;
+		*,--strategy-option=*)
+			newopt="$(expr " $1" : ' --strategy-option=\(.*\)')" ;;
+		*,-X*)
+			newopt="$(expr " $1" : ' -X\(.*\)')" ;;
+		1,*)
+			usage ;;
+		esac
+		strategy_opts="$strategy_opts $(git rev-parse --sq-quote "--$newopt")"
+		do_merge=t
+		if test -n "$strategy"
+		then
+			strategy=recursive
+		fi
+		;;
 	-s=*|--s=*|--st=*|--str=*|--stra=*|--strat=*|--strate=*|\
 		--strateg=*|--strategy=*|\
 	-s|--s|--st|--str|--stra|--strat|--strate|--strateg|--strategy)

t/t3402-rebase-merge.sh

@@ -74,6 +74,15 @@ test_expect_success 'rebase the other way' '
 	git rebase --merge side
 '
 
+test_expect_success 'rebase -Xtheirs' '
+	git checkout -b conflicting master~2 &&
+	echo "AB $T" >> original &&
+	git commit -mconflicting original &&
+	git rebase -Xtheirs master &&
+	grep AB original &&
+	! grep 11 original
+'
+
 test_expect_success 'merge and rebase should match' '
 	git diff-tree -r test-rebase test-merge >difference &&
 	if test -s difference