[PATCH 8/9] update-index: integrate with sparse index

["Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com>]

From: Victoria Dye <vdye@github.com>

Enable usage of the sparse index with `update-index`. Most variations of
`update-index` work without explicitly expanding the index or making any
other updates in or outside of `update-index.c`.

The one usage requiring additional changes is `--cacheinfo`; if a file
inside a sparse directory was specified, the index would not be expanded
until after the cache tree is invalidated, leading to a mismatch between the
index and cache tree. This scenario is handled by rearranging
`add_index_entry_with_check`, allowing `index_name_stage_pos` to expand the
index *before* attempting to invalidate the relevant cache tree path,
avoiding cache tree/index corruption.

Signed-off-by: Victoria Dye <vdye@github.com>
---
 builtin/update-index.c                   |  3 +++
 read-cache.c                             | 10 +++++++---
 t/t1092-sparse-checkout-compatibility.sh | 12 ++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/builtin/update-index.c b/builtin/update-index.c
index 187203e8bb5..605cc693bbd 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -1077,6 +1077,9 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 
 	git_config(git_default_config, NULL);
 
+	prepare_repo_settings(r);
+	the_repository->settings.command_requires_full_index = 0;
+
 	/* we will diagnose later if it turns out that we need to update it */
 	newfd = hold_locked_index(&lock_file, 0);
 	if (newfd < 0)
diff --git a/read-cache.c b/read-cache.c
index cbe73f14e5e..b4600e954b6 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1339,9 +1339,6 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
 	int new_only = option & ADD_CACHE_NEW_ONLY;
 
-	if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
-		cache_tree_invalidate_path(istate, ce->name);
-
 	/*
 	 * If this entry's path sorts after the last entry in the index,
 	 * we can avoid searching for it.
@@ -1352,6 +1349,13 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	else
 		pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce), EXPAND_SPARSE);
 
+	/*
+	 * Cache tree path should be invalidated only after index_name_stage_pos,
+	 * in case it expands a sparse index.
+	 */
+	if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
+		cache_tree_invalidate_path(istate, ce->name);
+
 	/* existing match? Just replace it. */
 	if (pos >= 0) {
 		if (!new_only)
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 6804ab23a27..bc0741c970d 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -1216,6 +1216,18 @@ test_expect_success 'sparse index is not expanded: blame' '
 	done
 '
 
+test_expect_success 'sparse index is not expanded: update-index' '
+	init_repos &&
+
+	echo "test" >sparse-index/README.md &&
+	echo "test2" >sparse-index/a &&
+	rm -f sparse-index/deep/a &&
+
+	ensure_not_expanded update-index --add README.md &&
+	ensure_not_expanded update-index a &&
+	ensure_not_expanded update-index --remove deep/a
+'
+
 # NEEDSWORK: a sparse-checkout behaves differently from a full checkout
 # in this scenario, but it shouldn't.
 test_expect_success 'reset mixed and checkout orphan' '
-- 
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