From: Junio C Hamano <gitster@pobox.com>
Date: Mon, 19 Dec 2016 22:45:38 +0000 (-0800)
Subject: Merge branch 'jc/pull-rebase-ff'
X-Git-Tag: v2.12.0-rc0~122
X-Git-Url: https://git.lorimer.id.au/gitweb.git/diff_plain/2fb11ec6c175e8a380d91daccc3bbf9fc5bbea8b?hp=101f3dc92a4cedb1f359f6ddce913b631ffa75b6

Merge branch 'jc/pull-rebase-ff'

"git pull --rebase", when there is no new commits on our side since
we forked from the upstream, should be able to fast-forward without
invoking "git rebase", but it didn't.

* jc/pull-rebase-ff:
pull: fast-forward "pull --rebase=true"
---

diff --git a/builtin/pull.c b/builtin/pull.c
index d6e46ee6d0..3ecb881b0b 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -857,10 +857,24 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 		if (merge_heads.nr > 1)
 			die(_("Cannot merge multiple branches into empty head."));
 		return pull_into_void(*merge_heads.sha1, curr_head);
-	} else if (opt_rebase) {
-		if (merge_heads.nr > 1)
-			die(_("Cannot rebase onto multiple branches."));
+	}
+	if (opt_rebase && merge_heads.nr > 1)
+		die(_("Cannot rebase onto multiple branches."));
+
+	if (opt_rebase) {
+		struct commit_list *list = NULL;
+		struct commit *merge_head, *head;
+
+		head = lookup_commit_reference(orig_head);
+		commit_list_insert(head, &list);
+		merge_head = lookup_commit_reference(merge_heads.sha1[0]);
+		if (is_descendant_of(merge_head, list)) {
+			/* we can fast-forward this without invoking rebase */
+			opt_ff = "--ff-only";
+			return run_merge();
+		}
 		return run_rebase(curr_head, *merge_heads.sha1, rebase_fork_point);
-	} else
+	} else {
 		return run_merge();
+	}
 }
diff --git a/t/t5520-pull.sh b/t/t5520-pull.sh
index 551844584f..17f4d0fe4e 100755
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -255,6 +255,23 @@ test_expect_success '--rebase' '
 	test new = "$(git show HEAD:file2)"
 '
 
+test_expect_success '--rebase fast forward' '
+	git reset --hard before-rebase &&
+	git checkout -b ff &&
+	echo another modification >file &&
+	git commit -m third file &&
+
+	git checkout to-rebase &&
+	git pull --rebase . ff &&
+	test "$(git rev-parse HEAD)" = "$(git rev-parse ff)" &&
+
+	# The above only validates the result.  Did we actually bypass rebase?
+	git reflog -1 >reflog.actual &&
+	sed "s/^[0-9a-f][0-9a-f]*/OBJID/" reflog.actual >reflog.fuzzy &&
+	echo "OBJID HEAD@{0}: pull --rebase . ff: Fast-forward" >reflog.expected &&
+	test_cmp reflog.expected reflog.fuzzy
+'
+
 test_expect_success '--rebase with conflicts shows advice' '
 	test_when_finished "git rebase --abort; git checkout -f to-rebase" &&
 	git checkout -b seq &&