[PATCH v2 1/4] submodule: refuse to add repository with no commits

[Kyle Meyer <kyle@kyleam.com>]

When the path given to 'git submodule add' is an existing repository
that is not in the index, the repository is passed to 'git add'.  If
this repository doesn't have any commits, we don't get a useful
result: there is no subproject OID to track, and any untracked files
in the sub-repository are added to the current repository.

Detect if the path is a repository with no commits and abort to avoid
getting into this state.  Note that this check must come before the
'git add --dry-run' check because an upcoming commit will make 'git
add' fail in this situation.

Signed-off-by: Kyle Meyer <kyle@kyleam.com>
---
 git-submodule.sh           |  7 +++++++
 t/t7400-submodule-basic.sh | 11 ++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/git-submodule.sh b/git-submodule.sh
index 514ede2596..5a9dc9bf7e 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -231,6 +231,13 @@ cmd_add()
 		die "$(eval_gettext "'\$sm_path' already exists in the index and is not a submodule")"
 	fi
 
+	if test -d "$sm_path" &&
+		test -z $(git -C "$sm_path" rev-parse --show-cdup 2>/dev/null)
+	then
+	    git -C "$sm_path" rev-parse --verify -q HEAD >/dev/null ||
+	    die "$(eval_gettext "'\$sm_path' does not have any commits")"
+	fi
+
 	if test -z "$force" &&
 		! git add --dry-run --ignore-missing --no-warn-embedded-repo "$sm_path" > /dev/null 2>&1
 	then
diff --git a/t/t7400-submodule-basic.sh b/t/t7400-submodule-basic.sh
index aba2d4d6ee..6adf640143 100755
--- a/t/t7400-submodule-basic.sh
+++ b/t/t7400-submodule-basic.sh
@@ -46,6 +46,15 @@ test_expect_success 'submodule update aborts on missing gitmodules url' '
 	test_must_fail git submodule init
 '
 
+test_expect_success 'add aborts on repository with no commits' '
+	cat >expected <<-\EOF &&
+	'"'repo-no-commits'"' does not have any commits
+	EOF
+	git init repo-no-commits &&
+	test_must_fail git submodule add ../a ./repo-no-commits 2>actual &&
+	test_i18ncmp expected actual
+'
+
 test_expect_success 'setup - repository in init subdirectory' '
 	mkdir init &&
 	(
@@ -809,7 +818,7 @@ test_expect_success '../bar/a/b/c works with relative local path - ../foo/bar.gi
 		cp pristine-.git-config .git/config &&
 		cp pristine-.gitmodules .gitmodules &&
 		mkdir -p a/b/c &&
-		(cd a/b/c && git init) &&
+		(cd a/b/c && git init && test_commit msg) &&
 		git config remote.origin.url ../foo/bar.git &&
 		git submodule add ../bar/a/b/c ./a/b/c &&
 		git submodule init &&
-- 
2.21.0