pull: fast-forward "pull --rebase=true"

"git pull --rebase" always runs "git rebase" after fetching the
commit to serve as the new base, even when the new base is a
descendant of the current HEAD, i.e. we haven't done any work.

In such a case, we can instead fast-forward to the new base without
invoking the rebase process.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/pull.c b/builtin/pull.c
index bf3fd3f9c8d80ff84ace4150214118355585e917..2a41d415b2df1e789f8cf466306e92ec242923c1 100644 (file)
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -878,10 +878,24 @@ 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 a0013ee32f1940e32b4038d6cc9a39b218d794f1..7887b6d97b762c3792b05257528ae38e6289bb99 100755 (executable)
--- a/t/t5520-pull.sh
+++ b/t/t5520-pull.sh
@@ -237,6 +237,23 @@ 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 fails with multiple branches' '
        git reset --hard before-rebase &&
        test_must_fail git pull --rebase . copy master 2>err &&