diff options
Diffstat (limited to 'merge-base.c')
| -rw-r--r-- | merge-base.c | 264 |
1 files changed, 264 insertions, 0 deletions
diff --git a/merge-base.c b/merge-base.c new file mode 100644 index 0000000..4856ca0 --- /dev/null +++ b/merge-base.c @@ -0,0 +1,264 @@ +#include <stdlib.h> +#include "cache.h" +#include "commit.h" + +#define PARENT1 1 +#define PARENT2 2 +#define UNINTERESTING 4 + +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 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 used to fail to mark an + * ancestor of a merge base as UNINTERESTING before we introduced the + * postprocessing phase (mark_reachable_commits). + * + * 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 ended up showing E as an interesting merge base. + * The postprocessing phase re-injects C and continues traversal + * to contaminate D and E. + */ + +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); + } + } + } +} + +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) { + printf("%s\n", sha1_to_hex(rev1->object.sha1)); + return 0; + } + + parse_commit(rev1); + parse_commit(rev2); + + rev1->object.flags |= 1; + rev2->object.flags |= 2; + insert_by_date(rev1, &list); + insert_by_date(rev2, &list); + + while (interesting(list)) { + struct commit *commit = list->item; + 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 parents of a found merge uninteresting */ + flags |= UNINTERESTING; + } + parents = commit->parents; + while (parents) { + struct commit *p = parents->item; + parents = parents->next; + if ((p->object.flags & flags) == flags) + continue; + parse_commit(p); + p->object.flags |= flags; + insert_by_date(p, &list); + } + } + + if (!result) + 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; + unsigned char rev1key[20], rev2key[20]; + + setup_git_directory(); + git_config(git_default_config); + + 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) + usage(merge_base_usage); + if (get_sha1(argv[1], rev1key)) + die("Not a valid object name %s", argv[1]); + if (get_sha1(argv[2], rev2key)) + die("Not a valid object name %s", argv[2]); + rev1 = lookup_commit_reference(rev1key); + rev2 = lookup_commit_reference(rev2key); + if (!rev1 || !rev2) + return 1; + return merge_base(rev1, rev2); +} |