In add_to_cache(), we treat any directories as submodules, and complain if we can't resolve their HEAD. This call to resolve_gitlink_ref() was added by f937bc2f86 (add: error appropriately on repository with no commits, 2019-04-09), with the goal of improving the error message for empty repositories. But we already resolve the submodule HEAD in index_path(), which is where we find the actual oid we're going to use. Resolving it again here introduces some downsides: 1. It's more work, since we have to open up the submodule repository's files twice. 2. There are call paths that get to index_path() without going through add_to_cache(). For instance, we'd want a similar informative message if "git diff empty" finds that it can't resolve the submodule's HEAD. (In theory we can also get there through update-index, but AFAICT it refuses to consider directories as submodules at all, and just complains about them). 3. The resolution in index_path() catches more errors that we don't handle here. In particular, it will validate that the object format for the submodule matches that of the superproject. This isn't a bug, since our call in add_to_cache() throws away the oid it gets without looking at it. But it certainly caused confusion for me when looking at where the object-format check should go. So instead of resolving the submodule HEAD in add_to_cache(), let's just teach the call in index_path() to actually produce an error message (which it already does for other cases). That's probably what f937bc2f86 should have done in the first place, and it gives us a single point of resolution when adding a submodule to the index. The resulting output is slightly more verbose, as we propagate the error up the call stack, but I think that's OK (and again, matches many other errors we get when indexing fails). I've left the text of the error message as-is, though it is perhaps overly specific. There are many reasons that resolving the submodule HEAD might fail, though outside of corruption or system errors it is probably most likely that the submodule HEAD is simply on an unborn branch. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>