Teach "git merge" a new option "--fp-base-only" that tells it to
consider only merge bases that are on the first-parent chain.
This speeds up back-merges needed in the topic branch workflow. The
merge of 'master' back into 'next' used as an example in the RFD
article <xmqqmvi2sj8f.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, i.e.
git checkout 4868def05e && git merge 659889482a
in our history takes about 1.22-1.33 seconds without the series,
while running the latter "git merge" with the "--fp-base-only"
option takes about 0.54-0.59 seconds.
Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
---
Documentation/merge-options.txt | 9 +++++++++
builtin/merge.c | 15 ++++++++++++---
2 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/Documentation/merge-options.txt b/Documentation/merge-options.txt
index 5b4a62e936..7927f069e4 100644
--- a/Documentation/merge-options.txt
+++ b/Documentation/merge-options.txt
@@ -116,6 +116,15 @@ ifndef::git-pull[]
Note that not all merge strategies may support progress
reporting.
+--fp-base-only::
+ Instead of using all merge bases when computing the
+ three-way merge result, use only the merge bases on the
+ first-parent chain of the commits being merged. This
+ experimental feature is meant to be used when merging an
+ older integration branch back to a newer integration branch
+ in the topic-branch workflow.
+
+
endif::git-pull[]
--allow-unrelated-histories::
diff --git a/builtin/merge.c b/builtin/merge.c
index 0ae099f746..a38b878e61 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -88,6 +88,8 @@ enum ff_type {
static enum ff_type fast_forward = FF_ALLOW;
+static int fp_base_only;
+
static int option_parse_message(const struct option *opt,
const char *arg, int unset)
{
@@ -210,6 +212,8 @@ static struct option builtin_merge_options[] = {
{ OPTION_SET_INT, 0, "ff-only", &fast_forward, NULL,
N_("abort if fast-forward is not possible"),
PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, FF_ONLY },
+ OPT_BOOL(0, "fp-base-only", &fp_base_only,
+ N_("use only merge bases on first-parent chain")),
OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
OPT_BOOL(0, "verify-signatures", &verify_signatures,
N_("verify that the named commit has a valid GPG signature")),
@@ -1340,9 +1344,14 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
if (!remoteheads)
; /* already up-to-date */
- else if (!remoteheads->next)
- common = get_merge_bases(head_commit, remoteheads->item);
- else {
+ else if (!remoteheads->next) {
+ unsigned flags = MB_POSTCLEAN;
+ if (fp_base_only)
+ flags |= MB_FPCHAIN;
+ common = get_merge_bases_opt(head_commit,
+ 1, &remoteheads->item,
+ flags);
+ } else {
struct commit_list *list = remoteheads;
commit_list_insert(head_commit, &list);
common = get_octopus_merge_bases(list);
--
2.10.1-631-gb2c64dcf30