sparse-index: mark mv as sparse-index compatible

In-cone moves already work without expanding the index, since
index_name_pos() auto-expands sparse directory entries on demand.
For out-of-cone moves (--sparse), call ensure_full_index() up front
because the bulk iteration assumes individual file entries.

Without --sparse, moving a sparse directory should produce the
helpful "Use the --sparse option" hint.  The old code relied on full
index expansion to make the individual skip-worktree entries visible
to the error path.  Now that the index stays sparse, teach
empty_dir_has_sparse_contents() to recognize sparse directory entries
directly and short-circuit to the hint.  As a side effect the error
now names the directory the user typed rather than listing each file
inside it.

Add tests verifying that in-cone renames do not expand the index,
that out-of-cone moves without --sparse produce the hint, and that
--sparse triggers expansion.

Signed-off-by: Kristofer Karlsson <krka@spotify.com>

Author: spkrka

builtin/mv.c

@@ -28,6 +28,7 @@
 #include "strvec.h"
 #include "submodule.h"
 #include "entry.h"
+#include "sparse-index.h"
 
 static const char * const builtin_mv_usage[] = {
 	N_("git mv [-v] [-f] [-n] [-k] <source> <destination>"),
@@ -153,7 +154,11 @@ static int empty_dir_has_sparse_contents(const char *name)
 	int pos = index_name_pos(the_repository->index, with_slash, length);
 	const struct cache_entry *ce;
 
-	if (pos < 0) {
+	if (pos >= 0) {
+		ce = the_repository->index->cache[pos];
+		if (S_ISSPARSEDIR(ce->ce_mode))
+			ret = 1;
+	} else {
 		pos = -pos - 1;
 		if (pos >= the_repository->index->cache_nr)
 			goto free_return;
@@ -249,12 +254,15 @@ int cmd_mv(int argc,
 		usage_with_options(builtin_mv_usage, builtin_mv_options);
 
 	prepare_repo_settings(the_repository);
-	the_repository->settings.command_requires_full_index = 1;
+	the_repository->settings.command_requires_full_index = 0;
 
 	repo_hold_locked_index(the_repository, &lock_file, LOCK_DIE_ON_ERROR);
 	if (repo_read_index(the_repository) < 0)
 		die(_("index file corrupt"));
 
+	if (ignore_sparse)
+		ensure_full_index(the_repository->index);
+
 	internal_prefix_pathspec(&sources, prefix, argv, argc, 0);
 	CALLOC_ARRAY(modes, argc);
 
@@ -317,6 +325,10 @@ int cmd_mv(int argc,
 				if (!path_in_sparse_checkout(src_w_slash, the_repository->index) &&
 				    empty_dir_has_sparse_contents(src)) {
 					free(src_w_slash);
+					if (!ignore_sparse) {
+						string_list_append(&only_match_skip_worktree, src);
+						goto act_on_entry;
+					}
 					modes[i] |= SKIP_WORKTREE_DIR;
 					goto dir_check;
 				}

t/t1092-sparse-checkout-compatibility.sh

@@ -1558,6 +1558,24 @@ test_expect_success 'sparse-index is not expanded' '
 	)
 '
 
+test_expect_success 'sparse-index is not expanded: git mv' '
+	init_repos &&
+
+	ensure_not_expanded mv deep/a deep/renamed-a &&
+	ensure_not_expanded mv deep/deeper2 deep/moved-deeper2 &&
+
+	ensure_not_expanded reset --hard &&
+
+	# mv of a sparse directory without --sparse should fail with
+	# a useful hint, without expanding the index.
+	run_sparse_index_trace2 ! mv folder1 deep &&
+	test_region ! index ensure_full_index trace2.txt &&
+	grep "Use the --sparse option" sparse-index-error &&
+
+	ensure_not_expanded reset --hard &&
+	ensure_expanded mv --sparse folder1 deep
+'
+
 test_expect_success 'sparse-index is not expanded: merge conflict in cone' '
 	init_repos &&
 

t/t7002-mv-sparse-checkout.sh

@@ -238,7 +238,7 @@ test_expect_success 'refuse to move out-of-cone directory without --sparse' '
 
 	test_must_fail git mv folder1 sub 2>stderr &&
 	cat sparse_error_header >expect &&
-	echo folder1/file1 >>expect &&
+	echo folder1 >>expect &&
 	cat sparse_hint >>expect &&
 	test_cmp expect stderr
 '