rebase: factor out branch_base calculation

Separate out calculating the merge base between 'onto' and 'HEAD' from
the check for whether we can fast-forward or not. This means we can skip
the fast-forward checks when the rebase is forced and avoid calculating
the merge-base between 'HEAD' and 'onto' when --keep-base is given.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 74024f49dfebbf5ea8da2cb6406948eee2502a7c..9ee3ab62407c29c41dfbd32e45e89599a964a774 100644 (file)
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -865,13 +865,9 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
        struct commit_list *merge_bases = NULL;
        int res = 0;
 
-       merge_bases = get_merge_bases(onto, head);
-       if (!merge_bases || merge_bases->next) {
-               oidcpy(branch_base, null_oid());
-               goto done;
-       }
+       if (is_null_oid(branch_base))
+               goto done; /* fill_branch_base() found multiple merge bases */
 
-       oidcpy(branch_base, &merge_bases->item->object.oid);
        if (!oideq(branch_base, &onto->object.oid))
                goto done;
 
@@ -881,7 +877,6 @@ static int can_fast_forward(struct commit *onto, struct commit *upstream,
        if (!upstream)
                goto done;
 
-       free_commit_list(merge_bases);
        merge_bases = get_merge_bases(upstream, head);
        if (!merge_bases || merge_bases->next)
                goto done;
@@ -896,6 +891,20 @@ done:
        return res && is_linear_history(onto, head);
 }
 
+static void fill_branch_base(struct rebase_options *options,
+                           struct object_id *branch_base)
+{
+       struct commit_list *merge_bases = NULL;
+
+       merge_bases = get_merge_bases(options->onto, options->orig_head);
+       if (!merge_bases || merge_bases->next)
+               oidcpy(branch_base, null_oid());
+       else
+               oidcpy(branch_base, &merge_bases->item->object.oid);
+
+       free_commit_list(merge_bases);
+}
+
 static int parse_opt_am(const struct option *opt, const char *arg, int unset)
 {
        struct rebase_options *opts = opt->value;
@@ -1660,6 +1669,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
                if (!options.onto)
                        die(_("Does not point to a valid commit '%s'"),
                                options.onto_name);
+               fill_branch_base(&options, &branch_base);
        }
 
        if (options.fork_point > 0)
@@ -1689,13 +1699,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
         * Check if we are already based on onto with linear history,
         * in which case we could fast-forward without replacing the commits
         * with new commits recreated by replaying their changes.
-        *
-        * Note that can_fast_forward() initializes branch_base, so we have to
-        * call it before checking allow_preemptive_ff.
         */
-       if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
-                   options.orig_head, &branch_base) &&
-           allow_preemptive_ff) {
+       if (allow_preemptive_ff &&
+           can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+                            options.orig_head, &branch_base)) {
                int flag;
 
                if (!(options.flags & REBASE_FORCE)) {