Re: [PATCH v2 3/6] merge-ort: expand only for out-of-cone conflicts

From: Derrick Stolee <redacted>

Merge conflicts happen often enough to want to avoid expanding a sparse
index when they happen, as long as those conflicts are within the
sparse-checkout cone. If a conflict exists outside of the
sparse-checkout cone, then we still need to expand before iterating over
the index entries. This is critical to do in advance because of how the
original_cache_nr is tracked to allow inserting and replacing cache
entries.

Iterate over the conflicted files and check if any paths are outside of
the sparse-checkout cone. If so, then expand the full index.

Add a test that demonstrates that we do not expand the index, even when
we hit a conflict within the sparse-checkout cone.

Signed-off-by: Derrick Stolee <redacted>
---
 merge-ort.c                              | 13 +++++++---
 t/t1092-sparse-checkout-compatibility.sh | 30 ++++++++++++++++++++++--
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/merge-ort.c b/merge-ort.c
index 8e754b769e1..805f7c41397 100644
--- a/merge-ort.c
+++ b/merge-ort.c

@@ -4060,11 +4060,18 @@ static int record_conflicted_index_entries(struct merge_options *opt)

        /*
         * We are in a conflicted state. These conflicts might be inside
-        * sparse-directory entries, so expand the index preemtively.
-        * Also, we set original_cache_nr below, but that might change if
+        * sparse-directory entries, so check if any entries are outside
+        * of the sparse-checkout cone preemptively.
+        *
+        * We set original_cache_nr below, but that might change if
         * index_name_pos() calls ask for paths within sparse directories.
         */
-       ensure_full_index(index);
+       strmap_for_each_entry(&opt->priv->conflicted, &iter, e) {
+               if (!path_in_sparse_checkout(e->key, index)) {
+                       ensure_full_index(index);
+                       break;
+               }
+       }

        /* If any entries have skip_worktree set, we'll have to check 'em out */
        state.force = 1;

diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index dc56252865c..38afdf689a2 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh

@@ -617,8 +617,17 @@ test_expect_success 'sparse-index is expanded and converted back' '
 ensure_not_expanded () {
        rm -f trace2.txt &&
        echo >>sparse-index/untracked.txt &&
-       GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
-               git -C sparse-index "$@" &&
+
+       if test "$1" = "!"
+       then
+               shift &&
+               test_must_fail env \
+                       GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
+                       git -C sparse-index "$@" || return 1
+       else
+               GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
+                       git -C sparse-index "$@" || return 1
+       fi &&
        test_region ! index ensure_full_index trace2.txt
 }

@@ -658,6 +667,23 @@ test_expect_success 'sparse-index is not expanded' '
        )
 '

+test_expect_success 'sparse-index is not expanded: merge conflict in cone' '
+       init_repos &&
+
+       for side in right left
+       do
+               git -C sparse-index checkout -b expand-$side base &&
+               echo $side >sparse-index/deep/a &&
+               git -C sparse-index commit -a -m "$side" || return 1
+       done &&
+
+       (
+               sane_unset GIT_TEST_MERGE_ALGORITHM &&
+               git -C sparse-index config pull.twohead ort &&
+               ensure_not_expanded ! merge -m merged expand-right
+       )