mv: check if <destination> exists in index to handle overwriting

Originally, moving a sparse file into cone can result in unwarned
overwrite of existing entry. The expected behavior is that if the
<destination> exists in the entry, user should be prompted to supply
a [-f|--force] to carry out the operation, or the operation should
fail.

Add a check mechanism to do that.

Signed-off-by: Shaoxuan Yuan <[email protected]>
Acked-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ffyuanda

builtin/mv.c

@@ -202,11 +202,20 @@ int cmd_mv(int argc, const char **argv, const char *prefix)
 				bad = _("bad source");
 				goto act_on_entry;
 			}
-
-			if (!ignore_sparse)
+			if (!ignore_sparse) {
 				string_list_append(&only_match_skip_worktree, src);
-			else
+				goto act_on_entry;
+			}
+			/* Check if dst exists in index */
+			if (cache_name_pos(dst, strlen(dst)) < 0) {
 				modes[i] = SPARSE;
+				goto act_on_entry;
+			}
+			if (!force) {
+				bad = _("destination exists");
+				goto act_on_entry;
+			}
+			modes[i] = SPARSE;
 			goto act_on_entry;
 		}
 		if (!strncmp(src, dst, length) &&

t/t7002-mv-sparse-checkout.sh

@@ -262,7 +262,7 @@ test_expect_success 'can move out-of-cone file with --sparse' '
 	test_path_is_file sub/file1
 '
 
-test_expect_failure 'refuse to move sparse file to existing destination' '
+test_expect_success 'refuse to move sparse file to existing destination' '
 	test_when_finished "cleanup_sparse_checkout" &&
 	mkdir folder1 &&
 	touch folder1/file1 &&
@@ -275,7 +275,7 @@ test_expect_failure 'refuse to move sparse file to existing destination' '
 	test_cmp expect stderr
 '
 
-test_expect_failure 'move sparse file to existing destination with --force and --sparse' '
+test_expect_success 'move sparse file to existing destination with --force and --sparse' '
 	test_when_finished "cleanup_sparse_checkout" &&
 	mkdir folder1 &&
 	touch folder1/file1 &&