Make cherry-pick use rerere for conflict resolution.

Cherry-picking can be helped by reusing previous confliction
resolution by invoking rerere automatically.

Signed-off-by: Abhijit Menon-Sen <ams@toroid.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-revert.c

@@ -11,6 +11,7 @@
 #include "cache-tree.h"
 #include "diff.h"
 #include "revision.h"
+#include "rerere.h"
 
 /*
  * This implements the builtins revert and cherry-pick.
@@ -395,6 +396,7 @@ static int revert_or_cherry_pick(int argc, const char **argv)
 			die ("Error wrapping up %s", defmsg);
 		fprintf(stderr, "Automatic %s failed.%s\n",
 			me, help_msg(commit->object.sha1));
+		rerere();
 		exit(1);
 	}
 	if (commit_lock_file(&msg_file) < 0)

t/t3504-cherry-pick-rerere.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+
+test_description='cherry-pick should rerere for conflicts'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	echo foo >foo &&
+	git add foo && test_tick && git commit -q -m 1 &&
+	echo foo-master >foo &&
+	git add foo && test_tick && git commit -q -m 2 &&
+
+	git checkout -b dev HEAD^ &&
+	echo foo-dev >foo &&
+	git add foo && test_tick && git commit -q -m 3 &&
+	git config rerere.enabled true
+'
+
+test_expect_success 'conflicting merge' '
+	test_must_fail git merge master
+'
+
+test_expect_success 'fixup' '
+	echo foo-dev >foo &&
+	git add foo && test_tick && git commit -q -m 4 &&
+	git reset --hard HEAD^
+	echo foo-dev >expect
+'
+
+test_expect_success 'cherry-pick conflict' '
+	test_must_fail git cherry-pick master &&
+	test_cmp expect foo
+'
+
+test_expect_success 'reconfigure' '
+	git config rerere.enabled false
+	git reset --hard
+'
+
+test_expect_success 'cherry-pick conflict without rerere' '
+	test_must_fail git cherry-pick master &&
+	test_must_fail test_cmp expect foo
+'
+
+test_done