add/rm: allow adding sparse entries when virtual

Upstream, a20f704 (add: warn when asked to update SKIP_WORKTREE entries,
2021-04-08) modified how 'git add <pathspec>' works with cache entries
marked with the SKIP_WORKTREE bit. The intention is to prevent a user
from accidentally adding a path that is outside their sparse-checkout
definition but somehow matches an existing index entry.

A similar change for 'git rm' happened in d5f4b82 (rm: honor sparse
checkout patterns, 2021-04-08).

This breaks when using the virtual filesystem in VFS for Git. It is
rare, but we could be in a scenario where the user has staged a change
and then the file is projected away. If the user re-adds the file, then
this warning causes the command to fail with the advise message.

Disable this logic when core_virtualfilesystem is enabled.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

builtin/add.c

@@ -208,7 +208,11 @@ static int refresh(int verbose, const struct pathspec *pathspec)
 		}
 	}
 
-	if (only_match_skip_worktree.nr) {
+	/*
+	 * When using a virtual filesystem, we might re-add a path
+	 * that is currently virtual and we want that to succeed.
+	 */
+	if (only_match_skip_worktree.nr && !core_virtualfilesystem) {
 		advise_on_updating_sparse_paths(&only_match_skip_worktree);
 		ret = 1;
 	}
@@ -652,8 +656,11 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 			}
 		}
 
-
-		if (only_match_skip_worktree.nr) {
+		/*
+		 * When using a virtual filesystem, we might re-add a path
+		 * that is currently virtual and we want that to succeed.
+		 */
+		if (only_match_skip_worktree.nr && !core_virtualfilesystem) {
 			advise_on_updating_sparse_paths(&only_match_skip_worktree);
 			exit_status = 1;
 		}

builtin/rm.c

@@ -332,7 +332,11 @@ int cmd_rm(int argc, const char **argv, const char *prefix)
 				    *original ? original : ".");
 		}
 
-		if (only_match_skip_worktree.nr) {
+		/*
+		 * When using a virtual filesystem, we might re-add a path
+		 * that is currently virtual and we want that to succeed.
+		 */
+		if (only_match_skip_worktree.nr && !core_virtualfilesystem) {
 			advise_on_updating_sparse_paths(&only_match_skip_worktree);
 			ret = 1;
 		}