[PATCH 1/3] apply: integrate with the sparse index

From: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date: May 7, 2025, 00:55 UTC
Message-ID: <0e6e199cd19ef186fb10b192529269cafc47805a.1746579321.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1914.git.1746579320.gitgitgadget@gmail.com>

From: Derrick Stolee <stolee@gmail.com>

The sparse index allows storing directory entries in the index, marked with the skip-wortkree bit and pointing to a tree object. This may be an unexpected data shape for some implementation areas, so we are rolling it out incrementally on a builtin-per-builtin basis.

This change enables the sparse index for 'git apply'. The main motivation for this change is that 'git apply' is used as a child process of 'git add -p' and expanding the sparse index for each of those child processes can lead to significant performance issues.

The good news is that the actual index manipulation code used by 'git apply' is already integrated with the sparse index, so the only product change is to mark the builtin as allowing the sparse index so it isn't inflated on read.

The more involved part of this change is around adding tests that verify how 'git apply' behaves in a sparse-checkout environment and whether or not the index expands in certain operations.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 builtin/apply.c                          |  7 +++-
 t/t1092-sparse-checkout-compatibility.sh | 46 ++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/builtin/apply.c b/builtin/apply.c
index 84f1863d3ac3..a1e20c593d09 100644
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -12,7 +12,7 @@ static const char * const apply_usage[] = {
 int cmd_apply(int argc,
 	      const char **argv,
 	      const char *prefix,
-	      struct repository *repo UNUSED)
+	      struct repository *repo)
 {
 	int force_apply = 0;
 	int options = 0;
@@ -35,6 +35,11 @@ int cmd_apply(int argc,
 				   &state, &force_apply, &options,
 				   apply_usage);
 
+	if (repo) {
+		prepare_repo_settings(repo);
+		repo->settings.command_requires_full_index = 0;
+	}
+
 	if (check_apply_state(&state, force_apply))
 		exit(128);
 
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index f9b448792cb4..ab8bd371eff3 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -1340,6 +1340,30 @@ test_expect_success 'submodule handling' '
 	grep "160000 $(git -C initial-repo rev-parse HEAD) 0	modules/sub" cache
 '
 
+test_expect_success 'git apply functionality' '
+	init_repos &&
+
+	test_all_match git checkout base &&
+
+	git -C full-checkout diff base..merge-right -- deep >patch-in-sparse &&
+	git -C full-checkout diff base..merge-right -- folder2 >patch-outside &&
+
+	# Apply a patch to a file inside the sparse definition
+	test_all_match git apply --index --stat ../patch-in-sparse &&
+	test_all_match git status --porcelain=v2 &&
+
+	# Apply a patch to a file outside the sparse definition
+	test_sparse_match test_must_fail git apply ../patch-outside &&
+	grep "No such file or directory" sparse-checkout-err &&
+
+	# But it works with --index and --cached
+	test_all_match git apply --index --stat ../patch-outside &&
+	test_all_match git status --porcelain=v2 &&
+	test_all_match git reset --hard &&
+	test_all_match git apply --cached --stat ../patch-outside &&
+	test_all_match git status --porcelain=v2
+'
+
 # When working with a sparse index, some commands will need to expand the
 # index to operate properly. If those commands also write the index back
 # to disk, they need to convert the index to sparse before writing.
@@ -2345,6 +2369,28 @@ test_expect_success 'sparse-index is not expanded: check-attr' '
 	ensure_not_expanded check-attr -a --cached -- folder1/a
 '
 
+test_expect_success 'sparse-index is not expanded: git apply' '
+	init_repos &&
+
+	git -C sparse-index checkout base &&
+	git -C full-checkout diff base..merge-right -- deep >patch-in-sparse &&
+	git -C full-checkout diff base..merge-right -- folder2 >patch-outside &&
+
+	# Apply a patch to a file inside the sparse definition
+	ensure_not_expanded apply --index --stat ../patch-in-sparse &&
+
+	# Apply a patch to a file outside the sparse definition
+	# Fails when caring about the worktree.
+	ensure_not_expanded ! apply ../patch-outside &&
+
+	# Expands when using --index.
+	ensure_expanded apply --index ../patch-outside &&
+	git -C sparse-index reset --hard &&
+
+	# Does not expand when using --cached.
+	ensure_not_expanded apply --cached ../patch-outside
+'
+
 test_expect_success 'advice.sparseIndexExpanded' '
 	init_repos &&

-- 
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