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authorJunio C Hamano <gitster@pobox.com>2013-10-23 23:47:32 (GMT)
committerJunio C Hamano <gitster@pobox.com>2013-10-29 20:06:08 (GMT)
commitd96855ff517560650c62eca51a8bb78263f6a3ef (patch)
tree6fb9e42186c21d95b9c86af87eb8f8ed7a80d028 /builtin/merge-base.c
parent16e57aec7f672fabe38fa0e4d39252eb9c7a1563 (diff)
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merge-base: teach "--fork-point" mode
The "git pull --rebase" command computes the fork point of the branch being rebased using the reflog entries of the "base" branch (typically a remote-tracking branch) the branch's work was based on, in order to cope with the case in which the "base" branch has been rewound and rebuilt. For example, if the history looked like this: o---B1 / ---o---o---B2--o---o---o---Base \ B3 \ Derived where the current tip of the "base" branch is at Base, but earlier fetch observed that its tip used to be B3 and then B2 and then B1 before getting to the current commit, and the branch being rebased on top of the latest "base" is based on commit B3, it tries to find B3 by going through the output of "git rev-list --reflog base" (i.e. Base, B1, B2, B3) until it finds a commit that is an ancestor of the current tip "Derived". Internally, we have get_merge_bases_many() that can compute this with one-go. We would want a merge-base between Derived and a fictitious merge commit that would result by merging all the historical tips of "base". When such a commit exist, we should get a single result, which exactly match one of the reflog entries of "base". Teach "git merge-base" a new mode, "--fork-point", to compute exactly that. Helped-by: Martin von Zweigbergk <martinvonz@gmail.com> Helped-by: John Keeping <john@keeping.me.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'builtin/merge-base.c')
-rw-r--r--builtin/merge-base.c109
1 files changed, 109 insertions, 0 deletions
diff --git a/builtin/merge-base.c b/builtin/merge-base.c
index d39c910..a292323 100644
--- a/builtin/merge-base.c
+++ b/builtin/merge-base.c
@@ -1,6 +1,9 @@
#include "builtin.h"
#include "cache.h"
#include "commit.h"
+#include "refs.h"
+#include "diff.h"
+#include "revision.h"
#include "parse-options.h"
static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
@@ -27,6 +30,7 @@ static const char * const merge_base_usage[] = {
N_("git merge-base [-a|--all] --octopus <commit>..."),
N_("git merge-base --independent <commit>..."),
N_("git merge-base --is-ancestor <commit> <commit>"),
+ N_("git merge-base --fork-point <ref> [<commit>]"),
NULL
};
@@ -85,6 +89,103 @@ static int handle_is_ancestor(int argc, const char **argv)
return 1;
}
+struct rev_collect {
+ struct commit **commit;
+ int nr;
+ int alloc;
+ unsigned int initial : 1;
+};
+
+static void add_one_commit(unsigned char *sha1, struct rev_collect *revs)
+{
+ struct commit *commit;
+
+ if (is_null_sha1(sha1))
+ return;
+
+ commit = lookup_commit(sha1);
+ if (!commit ||
+ (commit->object.flags & TMP_MARK) ||
+ parse_commit(commit))
+ return;
+
+ ALLOC_GROW(revs->commit, revs->nr + 1, revs->alloc);
+ revs->commit[revs->nr++] = commit;
+ commit->object.flags |= TMP_MARK;
+}
+
+static int collect_one_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
+ const char *ident, unsigned long timestamp,
+ int tz, const char *message, void *cbdata)
+{
+ struct rev_collect *revs = cbdata;
+
+ if (revs->initial) {
+ revs->initial = 0;
+ add_one_commit(osha1, revs);
+ }
+ add_one_commit(nsha1, revs);
+ return 0;
+}
+
+static int handle_fork_point(int argc, const char **argv)
+{
+ unsigned char sha1[20];
+ char *refname;
+ const char *commitname;
+ struct rev_collect revs;
+ struct commit *derived;
+ struct commit_list *bases;
+ int i, ret = 0;
+
+ switch (dwim_ref(argv[0], strlen(argv[0]), sha1, &refname)) {
+ case 0:
+ die("No such ref: '%s'", argv[0]);
+ case 1:
+ break; /* good */
+ default:
+ die("Ambiguous refname: '%s'", argv[0]);
+ }
+
+ commitname = (argc == 2) ? argv[1] : "HEAD";
+ if (get_sha1(commitname, sha1))
+ die("Not a valid object name: '%s'", commitname);
+
+ derived = lookup_commit_reference(sha1);
+ memset(&revs, 0, sizeof(revs));
+ revs.initial = 1;
+ for_each_reflog_ent(refname, collect_one_reflog_ent, &revs);
+
+ for (i = 0; i < revs.nr; i++)
+ revs.commit[i]->object.flags &= ~TMP_MARK;
+
+ bases = get_merge_bases_many(derived, revs.nr, revs.commit, 0);
+
+ /*
+ * There should be one and only one merge base, when we found
+ * a common ancestor among reflog entries.
+ */
+ if (!bases || bases->next) {
+ ret = 1;
+ goto cleanup_return;
+ }
+
+ /* And the found one must be one of the reflog entries */
+ for (i = 0; i < revs.nr; i++)
+ if (&bases->item->object == &revs.commit[i]->object)
+ break; /* found */
+ if (revs.nr <= i) {
+ ret = 1; /* not found */
+ goto cleanup_return;
+ }
+
+ printf("%s\n", sha1_to_hex(bases->item->object.sha1));
+
+cleanup_return:
+ free_commit_list(bases);
+ return ret;
+}
+
int cmd_merge_base(int argc, const char **argv, const char *prefix)
{
struct commit **rev;
@@ -100,6 +201,8 @@ int cmd_merge_base(int argc, const char **argv, const char *prefix)
N_("list revs not reachable from others"), 'r'),
OPT_CMDMODE(0, "is-ancestor", &cmdmode,
N_("is the first one ancestor of the other?"), 'a'),
+ OPT_CMDMODE(0, "fork-point", &cmdmode,
+ N_("find where <commit> forked from reflog of <ref>"), 'f'),
OPT_END()
};
@@ -120,6 +223,12 @@ int cmd_merge_base(int argc, const char **argv, const char *prefix)
if (cmdmode == 'r' || cmdmode == 'o')
return handle_octopus(argc, argv, cmdmode == 'r', show_all);
+ if (cmdmode == 'f') {
+ if (argc < 1 || 2 < argc)
+ usage_with_options(merge_base_usage, options);
+ return handle_fork_point(argc, argv);
+ }
+
if (argc < 2)
usage_with_options(merge_base_usage, options);