[PATCH v2 05/13] merge-ort: support subtree shifting

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

From: Elijah Newren <newren@gmail.com>

merge-recursive has some simple code to support subtree shifting; copy
it over to merge-ort.  This fixes t6409.12 under
GIT_TEST_MERGE_ALGORITHM=ort.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-ort.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/merge-ort.c b/merge-ort.c
index c7083e3769aa..c4fe234d8972 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -3551,6 +3551,23 @@ void merge_finalize(struct merge_options *opt,
 
 /*** Function Grouping: helper functions for merge_incore_*() ***/
 
+static struct tree *shift_tree_object(struct repository *repo,
+				      struct tree *one, struct tree *two,
+				      const char *subtree_shift)
+{
+	struct object_id shifted;
+
+	if (!*subtree_shift) {
+		shift_tree(repo, &one->object.oid, &two->object.oid, &shifted, 0);
+	} else {
+		shift_tree_by(repo, &one->object.oid, &two->object.oid, &shifted,
+			      subtree_shift);
+	}
+	if (oideq(&two->object.oid, &shifted))
+		return two;
+	return lookup_tree(repo, &shifted);
+}
+
 static inline void set_commit_tree(struct commit *c, struct tree *t)
 {
 	c->maybe_tree = t;
@@ -3680,6 +3697,13 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt,
 {
 	struct object_id working_tree_oid;
 
+	if (opt->subtree_shift) {
+		side2 = shift_tree_object(opt->repo, side1, side2,
+					  opt->subtree_shift);
+		merge_base = shift_tree_object(opt->repo, side1, merge_base,
+					       opt->subtree_shift);
+	}
+
 	trace2_region_enter("merge", "collect_merge_info", opt->repo);
 	if (collect_merge_info(opt, merge_base, side1, side2) != 0) {
 		/*
-- 
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