[PATCH v3 3/3] add: error appropriately on repository with no commits

[Kyle Meyer <kyle@kyleam.com>]

The previous commit made 'git add' abort when given a repository that
doesn't have a commit checked out.  However, the output upon failure
isn't appropriate:

  % git add repo
  warning: adding embedded git repository: repo
  hint: You've added another git repository inside your current repository.
  hint: [...]
  error: unable to index file 'repo/'
  fatal: adding files failed

The hint doesn't apply in this case, and the error message doesn't
tell the user why 'repo' couldn't be added to the index.

Provide better output by teaching add_to_index() to error when given a
git directory where HEAD can't be resolved.  To avoid the embedded
repository warning and hint, call check_embedded_repo() only after
add_file_to_index() succeeds because, in general, its output doesn't
make sense if adding to the index fails.

Signed-off-by: Kyle Meyer <kyle@kyleam.com>
---
 builtin/add.c  |  3 ++-
 read-cache.c   |  3 +++
 t/t3700-add.sh | 11 +++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/builtin/add.c b/builtin/add.c
index db2dfa4350..dd18e5c9b6 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -374,11 +374,12 @@ static int add_files(struct dir_struct *dir, int flags)
 	}
 
 	for (i = 0; i < dir->nr; i++) {
-		check_embedded_repo(dir->entries[i]->name);
 		if (add_file_to_index(&the_index, dir->entries[i]->name, flags)) {
 			if (!ignore_add_errors)
 				die(_("adding files failed"));
 			exit_status = 1;
+		} else {
+			check_embedded_repo(dir->entries[i]->name);
 		}
 	}
 	return exit_status;
diff --git a/read-cache.c b/read-cache.c
index 4dc6de1b55..b4b68d6ec8 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -708,6 +708,7 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 	int add_option = (ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE|
 			  (intent_only ? ADD_CACHE_NEW_ONLY : 0));
 	int hash_flags = HASH_WRITE_OBJECT;
+	struct object_id oid;
 
 	if (flags & ADD_CACHE_RENORMALIZE)
 		hash_flags |= HASH_RENORMALIZE;
@@ -717,6 +718,8 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 
 	namelen = strlen(path);
 	if (S_ISDIR(st_mode)) {
+		if (resolve_gitlink_ref(path, "HEAD", &oid) < 0)
+			return error(_("'%s' does not have a commit checked out"), path);
 		while (namelen && path[namelen-1] == '/')
 			namelen--;
 	}
diff --git a/t/t3700-add.sh b/t/t3700-add.sh
index 5a8425962b..c325167b90 100755
--- a/t/t3700-add.sh
+++ b/t/t3700-add.sh
@@ -296,6 +296,17 @@ test_expect_success '"git add ." in empty repo' '
 	)
 '
 
+test_expect_success 'error on a repository with no commits' '
+	rm -fr empty &&
+	git init empty &&
+	test_must_fail git add empty >actual 2>&1 &&
+	cat >expect <<-EOF &&
+	error: '"'empty/'"' does not have a commit checked out
+	fatal: adding files failed
+	EOF
+	test_i18ncmp expect actual
+'
+
 test_expect_success 'git add --dry-run of existing changed file' "
 	echo new >>track-this &&
 	git add --dry-run track-this >actual 2>&1 &&
-- 
2.21.0