[PATCH v2 1/5] fetch/pull: use the sparse index

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

From: Derrick Stolee <dstolee@microsoft.com>

The 'git fetch' and 'git pull' commands parse the index in order to
determine if submodules exist. Without command_requires_full_index=0,
this will expand a sparse index, causing slow performance even when
there is no new data to fetch.

The .gitmodules file will never be inside a sparse directory entry, and
even if it was, the index_name_pos() method would expand the sparse
index if needed as we search for the path by name. These commands do not
iterate over the index, which is the typical thing we are careful about
when integrating with the sparse index.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/fetch.c                          |  2 ++
 builtin/pull.c                           |  2 ++
 t/t1092-sparse-checkout-compatibility.sh | 10 ++++++++++
 3 files changed, 14 insertions(+)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index f7abbc31ff1..1696b7791d4 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1993,6 +1993,8 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 	}
 
 	git_config(git_fetch_config, NULL);
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
 
 	argc = parse_options(argc, argv, prefix,
 			     builtin_fetch_options, builtin_fetch_usage, 0);
diff --git a/builtin/pull.c b/builtin/pull.c
index 1cfaf9f3436..7bce3bd80f9 100644
--- a/builtin/pull.c
+++ b/builtin/pull.c
@@ -994,6 +994,8 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 		set_reflog_message(argc, argv);
 
 	git_config(git_pull_config, NULL);
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
 
 	argc = parse_options(argc, argv, prefix, pull_options, pull_usage, 0);
 
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 83971174ac3..3ba19ba1c14 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -964,6 +964,16 @@ test_expect_success 'sparse index is not expanded: blame' '
 	done
 '
 
+test_expect_success 'sparse index is not expanded: fetch/pull' '
+	init_repos &&
+
+	git -C sparse-index remote add full "file://$(pwd)/full-checkout" &&
+	ensure_not_expanded fetch full &&
+	git -C full-checkout commit --allow-empty -m "for pull merge" &&
+	git -C sparse-index commit --allow-empty -m "for pull merge" &&
+	ensure_not_expanded pull full base
+'
+
 # 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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