[WIP v3 3/7] mv: check if out-of-cone file exists in index with SKIP_WORKTREE bit

[Shaoxuan Yuan <shaoxuan.yuan02@xxxxxxxxx>]

Originally, moving a <source> file which is not on-disk but exists in
index as a SKIP_WORKTREE enabled cache entry, "giv mv" command errors
out with "bad source".

Change the checking logic, so that such <source>
file makes "giv mv" command warns with "advise_on_updating_sparse_paths()"
instead of "bad source"; also user now can supply a "--sparse" flag so
this operation can be carried out successfully.

Signed-off-by: Shaoxuan Yuan <shaoxuan.yuan02@xxxxxxxxx>
---
 builtin/mv.c                  | 21 +++++++++++++++++++--
 t/t7002-mv-sparse-checkout.sh |  4 ++--
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/builtin/mv.c b/builtin/mv.c
index 1ca2c21da8..9d8494a2e4 100644
--- a/builtin/mv.c
+++ b/builtin/mv.c
@@ -185,11 +185,28 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 
 		length = strlen(src);
 		if (lstat(src, &st) < 0) {
-			/* only error if existence is expected. */
-			if (modes[i] != SPARSE) {
+			int pos;
+			const struct cache_entry *ce;
+
+			pos = cache_name_pos(src, length);
+			if (pos < 0) {
+				/* only error if existence is expected. */
+				if (modes[i] != SPARSE)
+					bad = _("bad source");
+				goto act_on_entry;
+			}
+
+			ce = active_cache[pos];
+			if (!ce_skip_worktree(ce)) {
 				bad = _("bad source");
 				goto act_on_entry;
 			}
+
+			if (!ignore_sparse)
+				string_list_append(&only_match_skip_worktree, src);
+			else
+				modes[i] = SPARSE;
+			goto act_on_entry;
 		}
 		if (!strncmp(src, dst, length) &&
 		    (dst[length] == 0 || dst[length] == '/')) {
diff --git a/t/t7002-mv-sparse-checkout.sh b/t/t7002-mv-sparse-checkout.sh
index d6e7315a5a..1984cf131d 100755
--- a/t/t7002-mv-sparse-checkout.sh
+++ b/t/t7002-mv-sparse-checkout.sh
@@ -242,7 +242,7 @@ test_expect_failure 'can move out-of-cone directory with --sparse' '
 	test_path_is_file sub/folder1/file1
 '
 
-test_expect_failure 'refuse to move out-of-cone file without --sparse' '
+test_expect_success 'refuse to move out-of-cone file without --sparse' '
 	test_when_finished "cleanup_sparse_checkout" &&
 	setup_sparse_checkout &&
 
@@ -253,7 +253,7 @@ test_expect_failure 'refuse to move out-of-cone file without --sparse' '
 	test_cmp expect stderr
 '
 
-test_expect_failure 'can move out-of-cone file with --sparse' '
+test_expect_success 'can move out-of-cone file with --sparse' '
 	test_when_finished "cleanup_sparse_checkout" &&
 	setup_sparse_checkout &&
 
-- 
2.35.1