Junio C Hamano <gits...@pobox.com> writes:

>> Is it possible to change the behavior of "git pull 
>> --rebase=true|preserve|interactive" to use a fast forward merge if the 
>> remote branch is ahead and the local branch contains no new commits? 
>
> Interesting.  I do not think of a reason why we shouldn't.
>
> If we were still working in scripted Porcelain, it would have been a
> five minute hack, perhaps like this.
>
>  contrib/examples/git-pull.sh | 8 ++++++++
>  1 file changed, 8 insertions(+)

... and if we have to work with built-ins, it becomes a lot larger
than a five-minute hack, unfortunately.

Something like this may have a chance of working ;-)

 builtin/pull.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/builtin/pull.c b/builtin/pull.c
index bf3fd3f..777ae56 100644
--- 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();
 }
--
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