[PATCH 9/9] update-index: reduce scope of index expansion in do_reupdate

["Victoria Dye via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Victoria Dye <vdye@xxxxxxxxxx>

Expand the full index (and redo reupdate operation) only if a sparse
directory in the index differs from HEAD. Only the index entries that differ
between the index and HEAD are updated when performing `git update-index
--again`, so unmodified sparse directories are safely skipped. The index
does need to be expanded when sparse directories contain changes, though,
because `update_one(...)` will not operate on sparse directory index
entries.

Because the index should only be expanded if a sparse directory is modified,
add a test ensuring the index is not expanded when differences only exist
within the sparse cone.

Signed-off-by: Victoria Dye <vdye@xxxxxxxxxx>
---
 builtin/update-index.c                   | 14 +++++++++++---
 t/t1092-sparse-checkout-compatibility.sh |  5 ++++-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/builtin/update-index.c b/builtin/update-index.c
index 605cc693bbd..52ecc714d99 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -606,7 +606,7 @@ static struct cache_entry *read_one_ent(const char *which,
 			error("%s: not in %s branch.", path, which);
 		return NULL;
 	}
-	if (mode == S_IFDIR) {
+	if (!the_index.sparse_index && mode == S_IFDIR) {
 		if (which)
 			error("%s: not a blob in %s branch.", path, which);
 		return NULL;
@@ -743,8 +743,6 @@ static int do_reupdate(int ac, const char **av,
 		 */
 		has_head = 0;
  redo:
-	/* TODO: audit for interaction with sparse-index. */
-	ensure_full_index(&the_index);
 	for (pos = 0; pos < active_nr; pos++) {
 		const struct cache_entry *ce = active_cache[pos];
 		struct cache_entry *old = NULL;
@@ -761,6 +759,16 @@ static int do_reupdate(int ac, const char **av,
 			discard_cache_entry(old);
 			continue; /* unchanged */
 		}
+
+		/* At this point, we know the contents of the sparse directory are
+		 * modified with respect to HEAD, so we expand the index and restart
+		 * to process each path individually
+		 */
+		if (S_ISSPARSEDIR(ce->ce_mode)) {
+			ensure_full_index(&the_index);
+			goto redo;
+		}
+
 		/* Be careful.  The working tree may not have the
 		 * path anymore, in which case, under 'allow_remove',
 		 * or worse yet 'allow_replace', active_nr may decrease.
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index bc0741c970d..0863c9747c4 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -1225,7 +1225,10 @@ test_expect_success 'sparse index is not expanded: update-index' '
 
 	ensure_not_expanded update-index --add README.md &&
 	ensure_not_expanded update-index a &&
-	ensure_not_expanded update-index --remove deep/a
+	ensure_not_expanded update-index --remove deep/a &&
+
+	ensure_not_expanded reset --soft update-deep &&
+	ensure_not_expanded update-index --add --remove --again
 '
 
 # NEEDSWORK: a sparse-checkout behaves differently from a full checkout
-- 
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