[PATCH 2/3] git add: make -p/-i aware of sparse index

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <stolee@gmail.com>

It is slow to expand a sparse index in-memory due to parsing of trees.
We aim to minimize that performance cost when possible. 'git add -p'
uses 'git apply' child processes to modify the index, but still there
are some expansions that occur.

It turns out that control flows out of cmd_add() in the interactive
cases before the lines that confirm that the builtin is integrated with
the sparse index. We need to move that earlier to ensure it prevents a
full index expansion on read.

Add more test cases that confirm that these interactive add options work
with the sparse index. One interesting aspect here is that the '-i'
option avoids expanding the sparse index when a sparse directory exists
on disk while the '-p' option does hit the ensure_full_index() method.
This leaves some room for improvement, but this case should be atypical
as users should remain within their sparse-checkout.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 builtin/add.c                            |  7 +--
 t/t1092-sparse-checkout-compatibility.sh | 56 ++++++++++++++++++++++++
 2 files changed, 60 insertions(+), 3 deletions(-)

diff --git a/builtin/add.c b/builtin/add.c
index 747511b68bc3..7c292ffdc6c2 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -390,6 +390,10 @@ int cmd_add(int argc,
 
 	argc = parse_options(argc, argv, prefix, builtin_add_options,
 			  builtin_add_usage, PARSE_OPT_KEEP_ARGV0);
+
+	prepare_repo_settings(repo);
+	repo->settings.command_requires_full_index = 0;
+
 	if (patch_interactive)
 		add_interactive = 1;
 	if (add_interactive) {
@@ -426,9 +430,6 @@ int cmd_add(int argc,
 	add_new_files = !take_worktree_changes && !refresh_only && !add_renormalize;
 	require_pathspec = !(take_worktree_changes || (0 < addremove_explicit));
 
-	prepare_repo_settings(repo);
-	repo->settings.command_requires_full_index = 0;
-
 	repo_hold_locked_index(repo, &lock_file, LOCK_DIE_ON_ERROR);
 
 	/*
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index ab8bd371eff3..0dc5dd27184d 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -384,6 +384,38 @@ test_expect_success 'add, commit, checkout' '
 	test_all_match git checkout -
 '
 
+test_expect_success 'git add -p' '
+	init_repos &&
+
+	write_script edit-contents <<-\EOF &&
+	echo text >>$1
+	EOF
+
+	# Does not expand when edits are within sparse checkout.
+	run_on_all ../edit-contents deep/a &&
+	run_on_all ../edit-contents deep/deeper1/a &&
+
+	test_write_lines y n >in &&
+	run_on_all git add -p <in &&
+	test_all_match git status --porcelain=v2 &&
+	test_all_match git reset &&
+
+	test_write_lines u 1 "" q >in &&
+	run_on_all git add -i <in &&
+	test_all_match git status --porcelain=v2 &&
+	test_all_match git reset --hard &&
+
+	run_on_sparse mkdir -p folder1 &&
+	run_on_all ../edit-contents folder1/a &&
+	test_write_lines y n y >in &&
+	run_on_all git add -p <in &&
+	test_sparse_match git status --porcelain=v2 &&
+	test_sparse_match git reset &&
+	test_write_lines u 2 3 "" q >in &&
+	run_on_all git add -i <in &&
+	test_sparse_match git status --porcelain=v2
+'
+
 test_expect_success 'deep changes during checkout' '
 	init_repos &&
 
@@ -2391,6 +2423,30 @@ test_expect_success 'sparse-index is not expanded: git apply' '
 	ensure_not_expanded apply --cached ../patch-outside
 '
 
+test_expect_success 'sparse-index is not expanded: git add -p' '
+	init_repos &&
+
+	# Does not expand when edits are within sparse checkout.
+	echo "new content" >sparse-index/deep/a &&
+	echo "new content" >sparse-index/deep/deeper1/a &&
+	test_write_lines y n >in &&
+	ensure_not_expanded add -p <in &&
+	git -C sparse-index reset &&
+	ensure_not_expanded add -i <in &&
+
+	mkdir -p sparse-index/folder1 &&
+	echo "new content" >sparse-index/folder1/a &&
+
+	# -p does expand when edits are outside sparse checkout.
+	test_write_lines y n y >in &&
+	ensure_expanded add -p <in &&
+
+	# but -i does not expand.
+	git -C sparse-index reset &&
+	test_write_lines u 2 3 "" q >in &&
+	ensure_not_expanded add -i <in
+'
+
 test_expect_success 'advice.sparseIndexExpanded' '
 	init_repos &&
 
-- 
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