[PATCH 4/7] read-tree: integrate with sparse index

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

From: Victoria Dye <vdye@github.com>

Enable use of sparse index in 'git read-tree'. The integration in this patch
is limited only to usage of 'read-tree' that does not need additional
functional changes for the sparse index to behave as expected (i.e., produce
the same user-facing results as a non-sparse index sparse-checkout). To
ensure no unexpected behavior occurs, the index is explicitly expanded when:

* '--no-sparse-checkout' is specified (because it disables sparse-checkout)
* '--prefix' is specified (if the prefix is inside a sparse directory, the
  prefixed tree cannot be properly traversed)
* two or more <tree-ish> arguments are specified ('twoway_merge' and
  'threeway_merge' do not yet support merging sparse directories)

Signed-off-by: Victoria Dye <vdye@github.com>
---
 builtin/read-tree.c                      | 21 +++++++++++++++++++--
 t/t1092-sparse-checkout-compatibility.sh | 11 +++++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 2109c4c9e5c..c2fdbc2657f 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -160,8 +160,6 @@ int cmd_read_tree(int argc, const char **argv, const char *cmd_prefix)
 	argc = parse_options(argc, argv, cmd_prefix, read_tree_options,
 			     read_tree_usage, 0);
 
-	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
-
 	prefix_set = opts.prefix ? 1 : 0;
 	if (1 < opts.merge + opts.reset + prefix_set)
 		die("Which one? -m, --reset, or --prefix?");
@@ -169,6 +167,11 @@ int cmd_read_tree(int argc, const char **argv, const char *cmd_prefix)
 	if (opts.reset)
 		opts.reset = UNPACK_RESET_OVERWRITE_UNTRACKED;
 
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
+
+	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
+
 	/*
 	 * NEEDSWORK
 	 *
@@ -210,6 +213,10 @@ int cmd_read_tree(int argc, const char **argv, const char *cmd_prefix)
 	if (opts.merge && !opts.index_only)
 		setup_work_tree();
 
+	/* TODO: audit sparse index behavior in unpack_trees */
+	if (opts.skip_sparse_checkout || opts.prefix)
+		ensure_full_index(&the_index);
+
 	if (opts.merge) {
 		switch (stage - 1) {
 		case 0:
@@ -219,11 +226,21 @@ int cmd_read_tree(int argc, const char **argv, const char *cmd_prefix)
 			opts.fn = opts.prefix ? bind_merge : oneway_merge;
 			break;
 		case 2:
+			/*
+			 * TODO: update twoway_merge to handle edit/edit conflicts in
+			 * sparse directories.
+			 */
+			ensure_full_index(&the_index);
 			opts.fn = twoway_merge;
 			opts.initial_checkout = is_cache_unborn();
 			break;
 		case 3:
 		default:
+			/*
+			 * TODO: update threeway_merge to handle edit/edit conflicts in
+			 * sparse directories.
+			 */
+			ensure_full_index(&the_index);
 			opts.fn = threeway_merge;
 			break;
 		}
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index 9d58da4e925..ae44451a0a9 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -1407,6 +1407,17 @@ test_expect_success 'sparse index is not expanded: fetch/pull' '
 	ensure_not_expanded pull full base
 '
 
+test_expect_success 'sparse index is not expanded: read-tree' '
+	init_repos &&
+
+	ensure_not_expanded checkout -b test-branch update-folder1 &&
+	for MERGE_TREES in "update-folder2"
+	do
+		ensure_not_expanded read-tree -mu $MERGE_TREES &&
+		ensure_not_expanded reset --hard HEAD || return 1
+	done
+'
+
 test_expect_success 'ls-files' '
 	init_repos &&
 
-- 
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