[PATCH v3 1/3] 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 a commit checked out, we don't get a
useful result: there is no subproject OID to track, and any untracked
files in the sub-repository are added as blobs in the top-level
repository.

To avoid getting into this state, abort if the path is a repository
that doesn't have a commit checked out.  Note that this check must
come before the 'git add --dry-run' check because the next commit will
make 'git add' fail when given a repository that doesn't have a commit
checked out.

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 2c0fb6d723..c88a05086e 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 a commit checked out")"
+	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..a208cb26e1 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 >expect <<-\EOF &&
+	'"'repo-no-commits'"' does not have a commit checked out
+	EOF
+	git init repo-no-commits &&
+	test_must_fail git submodule add ../a ./repo-no-commits 2>actual &&
+	test_i18ncmp expect 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