merge-ort: implement recursive merges

This series depends on en/merge-ort-2 (it does NOT depend on en/merge-ort-3 and can thus be reviewed/merged independently of it).

This short series adds handling of recursive merges (merging of multiple merge-bases to create a virtual merge base) to merge-ort. With this short series the number of test failures under GIT_TEST_MERGE_ALGORITHM=ort drops by 801 (from 1448 to 647).

Changes since v4:

* add an earlier patch in the series that moves reverse_commit_list(), as-is, to commit.c. This also shrinks what is now the second patch.

Elijah Newren (4):
commit: move reverse_commit_list() from merge-recursive
merge-ort: copy a few small helper functions from merge-recursive.c
merge-ort: make clear_internal_opts() aware of partial clearing
merge-ort: implement merge_incore_recursive()

 commit.c          |  11 +++++
 commit.h          |   3 ++
 merge-ort.c       | 121 +++++++++++++++++++++++++++++++++++++++++++---
 merge-ort.h       |  10 ++++
 merge-recursive.c |  11 -----
 5 files changed, 138 insertions(+), 18 deletions(-)

base-commit: c5a6f65527aa3b6f5d7cf25437a88d8727ab0646
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-814%2Fnewren%2Fort-recursive-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-814/newren/ort-recursive-v5
Pull-Request: https://github.com/gitgitgadget/git/pull/814

Range-diff vs v4:

 -:  ----------- > 1:  9052faeabe6 commit: move reverse_commit_list() from merge-recursive
 1:  dcf28565ad3 ! 2:  949741932e5 merge-ort: copy a few small helper functions from merge-recursive.c
     @@ merge-ort.c: void merge_finalize(struct merge_options *opt,
      +	commit->object.parsed = 1;
      +	return commit;
      +}
     -+
     -+MAYBE_UNUSED
     -+static struct commit_list *reverse_commit_list(struct commit_list *list)
     -+{
     -+	struct commit_list *previous = NULL, *current, *backup;
     -+	for (current = list; current; current = backup) {
     -+		backup = current->next;
     -+		current->next = previous;
     -+		previous = current;
     -+	}
     -+	return previous;
     -+}
      +
       static void merge_start(struct merge_options *opt, struct merge_result *result)
       {
 2:  bffc45c6570 = 3:  3852125c70b merge-ort: make clear_internal_opts() aware of partial clearing
 3:  f622d6905d0 ! 4:  63e30492ccb merge-ort: implement merge_incore_recursive()

@@ merge-ort.c: static inline void set_commit_tree(struct commit *c, struct tree *t
static struct commit *make_virtual_commit(struct repository *repo,
struct tree *tree,
const char *comment)
-@@ merge-ort.c: static struct commit *make_virtual_commit(struct repository *repo,
- return commit;
- }
-
--MAYBE_UNUSED
- static struct commit_list *reverse_commit_list(struct commit_list *list)
- {
- struct commit_list *previous = NULL, *current, *backup;
@@ merge-ort.c: static void merge_ort_nonrecursive_internal(struct merge_options *opt,
}
}

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