#define PARENT2 2
#define UNINTERESTING 4
-static int interesting(struct commit_list *list)
+static struct commit *interesting(struct commit_list *list)
{
while (list) {
struct commit *commit = list->item;
list = list->next;
if (commit->object.flags & UNINTERESTING)
continue;
- return 1;
+ return commit;
+ }
+ return NULL;
+}
+
+/*
+ * A pathological example of how this thing works.
+ *
+ * Suppose we had this commit graph, where chronologically
+ * the timestamp on the commit are A <= B <= C <= D <= E <= F
+ * and we are trying to figure out the merge base for E and F
+ * commits.
+ *
+ * F
+ * / \
+ * E A D
+ * \ / /
+ * B /
+ * \ /
+ * C
+ *
+ * First we push E and F to list to be processed. E gets bit 1
+ * and F gets bit 2. The list becomes:
+ *
+ * list=F(2) E(1), result=empty
+ *
+ * Then we pop F, the newest commit, from the list. Its flag is 2.
+ * We scan its parents, mark them reachable from the side that F is
+ * reachable from, and push them to the list:
+ *
+ * list=E(1) D(2) A(2), result=empty
+ *
+ * Next pop E and do the same.
+ *
+ * list=D(2) B(1) A(2), result=empty
+ *
+ * Next pop D and do the same.
+ *
+ * list=C(2) B(1) A(2), result=empty
+ *
+ * Next pop C and do the same.
+ *
+ * list=B(1) A(2), result=empty
+ *
+ * Now it is B's turn. We mark its parent, C, reachable from B's side,
+ * and push it to the list:
+ *
+ * list=C(3) A(2), result=empty
+ *
+ * Now pop C and notice it has flags==3. It is placed on the result list,
+ * and the list now contains:
+ *
+ * list=A(2), result=C(3)
+ *
+ * We pop A and do the same.
+ *
+ * list=B(3), result=C(3)
+ *
+ * Next, we pop B and something very interesting happens. It has flags==3
+ * so it is also placed on the result list, and its parents are marked
+ * uninteresting, retroactively, and placed back on the list:
+ *
+ * list=C(7), result=C(7) B(3)
+ *
+ * Now, list does not have any interesting commit. So we find the newest
+ * commit from the result list that is not marked uninteresting. Which is
+ * commit B.
+ *
+ *
+ * Another pathological example how this thing can fail to mark an ancestor
+ * of a merge base as UNINTERESTING without the postprocessing phase.
+ *
+ * 2
+ * H
+ * 1 / \
+ * G A \
+ * |\ / \
+ * | B \
+ * | \ \
+ * \ C F
+ * \ \ /
+ * \ D /
+ * \ | /
+ * \| /
+ * E
+ *
+ * list A B C D E F G H
+ * G1 H2 - - - - - - 1 2
+ * H2 E1 B1 - 1 - - 1 - 1 2
+ * F2 E1 B1 A2 2 1 - - 1 2 1 2
+ * E3 B1 A2 2 1 - - 3 2 1 2
+ * B1 A2 2 1 - - 3 2 1 2
+ * C1 A2 2 1 1 - 3 2 1 2
+ * D1 A2 2 1 1 1 3 2 1 2
+ * A2 2 1 1 1 3 2 1 2
+ * B3 2 3 1 1 3 2 1 2
+ * C7 2 3 7 1 3 2 1 2
+ *
+ * At this point, unfortunately, everybody in the list is
+ * uninteresting, so we fail to complete the following two
+ * steps to fully marking uninteresting commits.
+ *
+ * D7 2 3 7 7 3 2 1 2
+ * E7 2 3 7 7 7 2 1 2
+ *
+ * and we end up showing E as an interesting merge base.
+ */
+
+static int show_all = 0;
+
+static void mark_reachable_commits(struct commit_list *result,
+ struct commit_list *list)
+{
+ struct commit_list *tmp;
+
+ /*
+ * Postprocess to fully contaminate the well.
+ */
+ for (tmp = result; tmp; tmp = tmp->next) {
+ struct commit *c = tmp->item;
+ /* Reinject uninteresting ones to list,
+ * so we can scan their parents.
+ */
+ if (c->object.flags & UNINTERESTING)
+ commit_list_insert(c, &list);
+ }
+ while (list) {
+ struct commit *c = list->item;
+ struct commit_list *parents;
+
+ tmp = list;
+ list = list->next;
+ free(tmp);
+
+ /* Anything taken out of the list is uninteresting, so
+ * mark all its parents uninteresting. We do not
+ * parse new ones (we already parsed all the relevant
+ * ones).
+ */
+ parents = c->parents;
+ while (parents) {
+ struct commit *p = parents->item;
+ parents = parents->next;
+ if (!(p->object.flags & UNINTERESTING)) {
+ p->object.flags |= UNINTERESTING;
+ commit_list_insert(p, &list);
+ }
+ }
}
- return 0;
}
-static struct commit *common_ancestor(struct commit *rev1, struct commit *rev2)
+static int merge_base(struct commit *rev1, struct commit *rev2)
{
struct commit_list *list = NULL;
struct commit_list *result = NULL;
+ struct commit_list *tmp = NULL;
- if (rev1 == rev2)
- return rev1;
+ if (rev1 == rev2) {
+ printf("%s\n", sha1_to_hex(rev1->object.sha1));
+ return 0;
+ }
parse_commit(rev1);
parse_commit(rev2);
while (interesting(list)) {
struct commit *commit = list->item;
- struct commit_list *tmp = list, *parents;
+ struct commit_list *parents;
int flags = commit->object.flags & 7;
+ tmp = list;
list = list->next;
free(tmp);
if (flags == 3) {
insert_by_date(commit, &result);
- /* Mark children of a found merge uninteresting */
+ /* Mark parents of a found merge uninteresting */
flags |= UNINTERESTING;
}
parents = commit->parents;
insert_by_date(p, &list);
}
}
+
if (!result)
- return NULL;
- return result->item;
+ return 1;
+
+ if (result->next && list)
+ mark_reachable_commits(result, list);
+
+ while (result) {
+ struct commit *commit = result->item;
+ result = result->next;
+ if (commit->object.flags & UNINTERESTING)
+ continue;
+ printf("%s\n", sha1_to_hex(commit->object.sha1));
+ if (!show_all)
+ return 0;
+ commit->object.flags |= UNINTERESTING;
+ }
+ return 0;
}
+static const char merge_base_usage[] =
+"git-merge-base [--all] <commit-id> <commit-id>";
+
int main(int argc, char **argv)
{
- struct commit *rev1, *rev2, *ret;
+ struct commit *rev1, *rev2;
unsigned char rev1key[20], rev2key[20];
+ setup_git_directory();
+
+ while (1 < argc && argv[1][0] == '-') {
+ char *arg = argv[1];
+ if (!strcmp(arg, "-a") || !strcmp(arg, "--all"))
+ show_all = 1;
+ else
+ usage(merge_base_usage);
+ argc--; argv++;
+ }
if (argc != 3 ||
get_sha1(argv[1], rev1key) ||
- get_sha1(argv[2], rev2key)) {
- usage("git-merge-base <commit-id> <commit-id>");
- }
+ get_sha1(argv[2], rev2key))
+ usage(merge_base_usage);
rev1 = lookup_commit_reference(rev1key);
rev2 = lookup_commit_reference(rev2key);
if (!rev1 || !rev2)
return 1;
- ret = common_ancestor(rev1, rev2);
- if (!ret)
- return 1;
- printf("%s\n", sha1_to_hex(ret->object.sha1));
- return 0;
+ return merge_base(rev1, rev2);
}