pull: fast-forward working tree if head is updated

Since b10ac50 (Fix pulling into the same branch., 2005-08-25), git-pull,
upon detecting that git-fetch updated the current head, will
fast-forward the working tree to the updated head commit.

Re-implement this behavior.

Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/pull.c b/builtin/pull.c
index 1e688be4504d914774fa2629b3198f82a259fc0b..110e71948148f51d29288daf040667f4db12f5d1 100644 (file)
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -412,6 +412,7 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 {
        const char *repo, **refspecs;
        struct sha1_array merge_heads = SHA1_ARRAY_INIT;
+       unsigned char orig_head[GIT_SHA1_RAWSZ], curr_head[GIT_SHA1_RAWSZ];
 
        if (!getenv("_GIT_USE_BUILTIN_PULL")) {
                const char *path = mkpath("%s/git-pull", git_exec_path());
@@ -435,12 +436,41 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
        if (file_exists(git_path("MERGE_HEAD")))
                die_conclude_merge();
 
+       if (get_sha1("HEAD", orig_head))
+               hashclr(orig_head);
+
        if (run_fetch(repo, refspecs))
                return 1;
 
        if (opt_dry_run)
                return 0;
 
+       if (get_sha1("HEAD", curr_head))
+               hashclr(curr_head);
+
+       if (!is_null_sha1(orig_head) && !is_null_sha1(curr_head) &&
+                       hashcmp(orig_head, curr_head)) {
+               /*
+                * The fetch involved updating the current branch.
+                *
+                * The working tree and the index file are still based on
+                * orig_head commit, but we are merging into curr_head.
+                * Update the working tree to match curr_head.
+                */
+
+               warning(_("fetch updated the current branch head.\n"
+                       "fast-forwarding your working tree from\n"
+                       "commit %s."), sha1_to_hex(orig_head));
+
+               if (checkout_fast_forward(orig_head, curr_head, 0))
+                       die(_("Cannot fast-forward your working tree.\n"
+                               "After making sure that you saved anything precious from\n"
+                               "$ git diff %s\n"
+                               "output, run\n"
+                               "$ git reset --hard\n"
+                               "to recover."), sha1_to_hex(orig_head));
+       }
+
        get_merge_heads(&merge_heads);
 
        if (!merge_heads.nr)