[PATCH v4 0/3] merge-ort: implement recursive merges

["Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com>]

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 v3:

 * remove the confusing portions of the merge_incore_recursive() API around
   opt->ancestor that were designed to accommodate merge_recursive_generic()
   or some function like it. If that stuff is really needed, we can add it
   later, but it may be better to simply adjust merge_recursive_generic()
   and/or its callers when we get to that point in the porting process.

Elijah Newren (3):
  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()

 merge-ort.c | 132 +++++++++++++++++++++++++++++++++++++++++++++++++---
 merge-ort.h |  10 ++++
 2 files changed, 135 insertions(+), 7 deletions(-)


base-commit: c5a6f65527aa3b6f5d7cf25437a88d8727ab0646
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-814%2Fnewren%2Fort-recursive-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-814/newren/ort-recursive-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/814

Range-diff vs v3:

 1:  dcf28565ad3 = 1:  dcf28565ad3 merge-ort: copy a few small helper functions from merge-recursive.c
 2:  bffc45c6570 = 2:  bffc45c6570 merge-ort: make clear_internal_opts() aware of partial clearing
 3:  59216a155ae ! 3:  f622d6905d0 merge-ort: implement merge_incore_recursive()
     @@ merge-ort.c: static void merge_ort_nonrecursive_internal(struct merge_options *o
      +		merged_merge_bases = make_virtual_commit(opt->repo, tree,
      +							 "ancestor");
      +		ancestor_name = "empty tree";
     -+	} else if (opt->ancestor && !opt->priv->call_depth) {
     -+		ancestor_name = opt->ancestor;
      +	} else if (merge_bases) {
      +		ancestor_name = "merged common ancestors";
      +	} else {
     @@ merge-ort.c: void merge_incore_recursive(struct merge_options *opt,
       			    struct merge_result *result)
       {
      -	die("Not yet implemented");
     -+	/*
     -+	 * merge_incore_nonrecursive() exists for cases where we always
     -+	 * know there is a well-defined single merge base.  However,
     -+	 * despite a similar structure, merge-recursive.c noted that some
     -+	 * callers preferred to call the recursive logic anyway and still
     -+	 * set a special name for opt->ancestor that would appear in
     -+	 * merge.conflictStyle=diff3 output.
     -+	 *
     -+	 * git-am was one such example (it wanted to set opt->ancestor to
     -+	 * "constructed merge base", since it created a fake merge base);
     -+	 * it called the recursive merge logic through a special
     -+	 * merge_recursive_generic() wrapper.
     -+	 *
     -+	 * Allow the same kind of special case here.
     -+	 */
     -+	int num_merge_bases_is_1 = (merge_bases && !merge_bases->next);
     -+	assert(opt->ancestor == NULL || num_merge_bases_is_1);
     ++	/* We set the ancestor label based on the merge_bases */
     ++	assert(opt->ancestor == NULL);
      +
      +	merge_start(opt, result);
      +	merge_ort_internal(opt, merge_bases, side1, side2, result);

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