built-in rebase: reinstate `checkout -q` behavior where appropriate

When we converted a `git checkout -q $onto^0` call to use
`reset_head()`, we inadvertently incurred a change from a twoway_merge
to a oneway_merge, as if we wanted a `git reset --hard` instead.

This has performance ramifications under certain, though, as the
oneway_merge needs to lstat() every single index entry whereas
twoway_merge does not.

So let's go back to the old behavior.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 074594cf1055bde5a873fd623c881272e14b936f..dc78c1497dee8eb9a278606cf109c424d128c3d7 100644 (file)
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -523,14 +523,16 @@ finished_rebase:
 #define GIT_REFLOG_ACTION_ENVIRONMENT "GIT_REFLOG_ACTION"
 
 #define RESET_HEAD_DETACH (1<<0)
+#define RESET_HEAD_HARD (1<<1)
 
 static int reset_head(struct object_id *oid, const char *action,
                      const char *switch_to_branch, unsigned flags,
                      const char *reflog_orig_head, const char *reflog_head)
 {
        unsigned detach_head = flags & RESET_HEAD_DETACH;
+       unsigned reset_hard = flags & RESET_HEAD_HARD;
        struct object_id head_oid;
-       struct tree_desc desc;
+       struct tree_desc desc[2] = { { NULL }, { NULL } };
        struct lock_file lock = LOCK_INIT;
        struct unpack_trees_options unpack_tree_opts;
        struct tree *tree;
@@ -539,7 +541,7 @@ static int reset_head(struct object_id *oid, const char *action,
        size_t prefix_len;
        struct object_id *orig = NULL, oid_orig,
                *old_orig = NULL, oid_old_orig;
-       int ret = 0;
+       int ret = 0, nr = 0;
 
        if (switch_to_branch && !starts_with(switch_to_branch, "refs/"))
                BUG("Not a fully qualified branch: '%s'", switch_to_branch);
@@ -549,20 +551,20 @@ static int reset_head(struct object_id *oid, const char *action,
                goto leave_reset_head;
        }
 
-       if (!oid) {
-               if (get_oid("HEAD", &head_oid)) {
-                       ret = error(_("could not determine HEAD revision"));
-                       goto leave_reset_head;
-               }
-               oid = &head_oid;
+       if ((!oid || !reset_hard) && get_oid("HEAD", &head_oid)) {
+               ret = error(_("could not determine HEAD revision"));
+               goto leave_reset_head;
        }
 
+       if (!oid)
+               oid = &head_oid;
+
        memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
        setup_unpack_trees_porcelain(&unpack_tree_opts, action);
        unpack_tree_opts.head_idx = 1;
        unpack_tree_opts.src_index = the_repository->index;
        unpack_tree_opts.dst_index = the_repository->index;
-       unpack_tree_opts.fn = oneway_merge;
+       unpack_tree_opts.fn = reset_hard ? oneway_merge : twoway_merge;
        unpack_tree_opts.update = 1;
        unpack_tree_opts.merge = 1;
        if (!detach_head)
@@ -573,12 +575,17 @@ static int reset_head(struct object_id *oid, const char *action,
                goto leave_reset_head;
        }
 
-       if (!fill_tree_descriptor(&desc, oid)) {
+       if (!reset_hard && !fill_tree_descriptor(&desc[nr++], &head_oid)) {
+               ret = error(_("failed to find tree of %s"), oid_to_hex(oid));
+               goto leave_reset_head;
+       }
+
+       if (!fill_tree_descriptor(&desc[nr++], oid)) {
                ret = error(_("failed to find tree of %s"), oid_to_hex(oid));
                goto leave_reset_head;
        }
 
-       if (unpack_trees(1, &desc, &unpack_tree_opts)) {
+       if (unpack_trees(nr, desc, &unpack_tree_opts)) {
                ret = -1;
                goto leave_reset_head;
        }
@@ -625,7 +632,8 @@ static int reset_head(struct object_id *oid, const char *action,
 leave_reset_head:
        strbuf_release(&msg);
        rollback_lock_file(&lock);
-       free((void *)desc.buffer);
+       while (nr)
+               free((void *)desc[--nr].buffer);
        return ret;
 }
 
@@ -1003,7 +1011,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
                rerere_clear(&merge_rr);
                string_list_clear(&merge_rr, 1);
 
-               if (reset_head(NULL, "reset", NULL, 0, NULL, NULL) < 0)
+               if (reset_head(NULL, "reset", NULL, RESET_HEAD_HARD,
+                              NULL, NULL) < 0)
                        die(_("could not discard worktree changes"));
                if (read_basic_state(&options))
                        exit(1);
@@ -1019,7 +1028,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
                if (read_basic_state(&options))
                        exit(1);
                if (reset_head(&options.orig_head, "reset",
-                              options.head_name, 0, NULL, NULL) < 0)
+                              options.head_name, RESET_HEAD_HARD,
+                              NULL, NULL) < 0)
                        die(_("could not move back to %s"),
                            oid_to_hex(&options.orig_head));
                ret = finish_rebase(&options);
@@ -1383,7 +1393,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
                        write_file(autostash, "%s", oid_to_hex(&oid));
                        printf(_("Created autostash: %s\n"), buf.buf);
                        if (reset_head(&head->object.oid, "reset --hard",
-                                      NULL, 0, NULL, NULL) < 0)
+                                      NULL, RESET_HEAD_HARD, NULL, NULL) < 0)
                                die(_("could not reset --hard"));
                        printf(_("HEAD is now at %s"),
                               find_unique_abbrev(&head->object.oid,