commit: integrate with sparse-index

Update 'git commit' to allow using the sparse-index in memory without
expanding to a full one. The only place that had an ensure_full_index()
call was in cache_tree_update(). The recursive algorithm for
update_one() was already updated in 2de37c5 (cache-tree: integrate
with sparse directory entries, 2021-03-03) to handle sparse directory
entries in the index.

Most of this change involves testing different command-line options that
allow specifying which on-disk changes should be included in the commit.
This includes no options (only take currently-staged changes), -a (take
all tracked changes), and --include (take a list of specific changes).
To simplify testing that these options do not expand the index, update
the test that previously verified that 'git status' does not expand the
index with a helper method, ensure_not_expanded().

This allows 'git commit' to operate much faster when the sparse-checkout
cone is much smaller than the full list of files at HEAD.

Here are the relevant lines from p2000-sparse-operations.sh:

Test                                      HEAD~1           HEAD
----------------------------------------------------------------------------------
2000.14: git commit -a -m A (full-v3)     0.35(0.26+0.06)  0.36(0.28+0.07) +2.9%
2000.15: git commit -a -m A (full-v4)     0.32(0.26+0.05)  0.34(0.28+0.06) +6.3%
2000.16: git commit -a -m A (sparse-v3)   0.63(0.59+0.06)  0.04(0.05+0.05) -93.7%
2000.17: git commit -a -m A (sparse-v4)   0.64(0.59+0.08)  0.04(0.04+0.04) -93.8%

It is important to compare the full-index case to the sparse-index case,
so the improvement for index version v4 is actually an 88% improvement in
this synthetic example.

In a real repository with over two million files at HEAD and 60,000
files in the sparse-checkout definition, the time for 'git commit -a'
went from 2.61 seconds to 134ms. I compared this to the result if the
index only contained the paths in the sparse-checkout definition and
found the theoretical optimum to be 120ms, so the out-of-cone paths only
add a 12% overhead.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -1682,6 +1682,9 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage_with_options(builtin_commit_usage, builtin_commit_options);
 
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
+
 	status_init_config(&s, git_commit_config);
 	s.commit_template = 1;
 	status_format = STATUS_FORMAT_NONE; /* Ignore status.short */

cache-tree.c

@@ -461,8 +461,6 @@ int cache_tree_update(struct index_state *istate, int flags)
 	if (i)
 		return i;
 
-	ensure_full_index(istate);
-
 	if (!istate->cache_tree)
 		istate->cache_tree = cache_tree();
 

t/t1092-sparse-checkout-compatibility.sh

@@ -262,6 +262,34 @@ test_expect_success 'add, commit, checkout' '
 	test_all_match git checkout -
 '
 
+test_expect_success 'commit including unstaged changes' '
+	init_repos &&
+
+	write_script edit-file <<-\EOF &&
+	echo $1 >$2
+	EOF
+
+	run_on_all ../edit-file 1 a &&
+	run_on_all ../edit-file 1 deep/a &&
+
+	test_all_match git commit -m "-a" -a &&
+	test_all_match git status --porcelain=v2 &&
+
+	run_on_all ../edit-file 2 a &&
+	run_on_all ../edit-file 2 deep/a &&
+
+	test_all_match git commit -m "--include" --include deep/a &&
+	test_all_match git status --porcelain=v2 &&
+	test_all_match git commit -m "--include" --include a &&
+	test_all_match git status --porcelain=v2 &&
+
+	run_on_all ../edit-file 3 a &&
+	run_on_all ../edit-file 3 deep/a &&
+
+	test_all_match git commit -m "--amend" -a --amend &&
+	test_all_match git status --porcelain=v2
+'
+
 test_expect_success 'status/add: outside sparse cone' '
 	init_repos &&
 
@@ -514,14 +542,25 @@ test_expect_success 'sparse-index is expanded and converted back' '
 	test_region index ensure_full_index trace2.txt
 '
 
-test_expect_success 'sparse-index is not expanded' '
-	init_repos &&
-
+ensure_not_expanded () {
 	rm -f trace2.txt &&
 	echo >>sparse-index/untracked.txt &&
 	GIT_TRACE2_EVENT="$(pwd)/trace2.txt" GIT_TRACE2_EVENT_NESTING=10 \
-		git -C sparse-index status &&
+		git -C sparse-index "$@" &&
 	test_region ! index ensure_full_index trace2.txt
+}
+
+test_expect_success 'sparse-index is not expanded' '
+	init_repos &&
+
+	ensure_not_expanded status &&
+	ensure_not_expanded commit --allow-empty -m empty &&
+	echo >>sparse-index/a &&
+	ensure_not_expanded commit -a -m a &&
+	echo >>sparse-index/a &&
+	ensure_not_expanded commit --include a -m a &&
+	echo >>sparse-index/deep/deeper1/a &&
+	ensure_not_expanded commit --include deep/deeper1/a -m deeper
 '
 
 # NEEDSWORK: a sparse-checkout behaves differently from a full checkout