Merge branch 'jc/submodule-add' into seen

"git submodule add" to add a submodule under <name> segfaulted,
when a submodule.<name>.something is already in .gitmodules file
without defining where its submodule.<name>.path is, which has been
corrected.

Comments?

* jc/submodule-add:
  submodule add: sanity check existing .gitmodules

Author: gitster

builtin/submodule--helper.c

@@ -1903,6 +1903,13 @@ static int determine_submodule_update_strategy(struct repository *r,
 	const char *val;
 	int ret;
 
+	/*
+	 * NEEDSWORK: audit and ensure that update_submodule() has right
+	 * to assume that submodule_from_path() above will always succeed.
+	 */
+	if (!sub)
+		BUG("update_submodule assumes a submodule exists at path (%s)",
+		    path);
 	key = xstrfmt("submodule.%s.update", sub->name);
 
 	if (update) {
@@ -3527,14 +3534,15 @@ static int module_add(int argc, const char **argv, const char *prefix,
 		}
 	}
 
-	if(!add_data.sm_name)
+	if (!add_data.sm_name)
 		add_data.sm_name = add_data.sm_path;
 
 	existing = submodule_from_name(the_repository,
 					null_oid(the_hash_algo),
 					add_data.sm_name);
 
-	if (existing && strcmp(existing->path, add_data.sm_path)) {
+	if (existing && existing->path &&
+	    strcmp(existing->path, add_data.sm_path)) {
 		if (!force) {
 			die(_("submodule name '%s' already used for path '%s'"),
 			    add_data.sm_name, existing->path);

t/t7400-submodule-basic.sh

@@ -48,6 +48,25 @@ test_expect_success 'submodule deinit works on empty repository' '
 	git submodule deinit --all
 '
 
+test_expect_success 'submodule add with incomplete .gitmodules' '
+	test_when_finished "rm -f expect actual" &&
+	test_when_finished "git config remove-section submodule.one" &&
+	test_when_finished "git rm -f one .gitmodules" &&
+	git init one &&
+	git -C one commit --allow-empty -m one-initial &&
+	git config -f .gitmodules submodule.one.ignore all &&
+
+	git submodule add ./one &&
+
+	for var in ignore path url
+	do
+		git config -f .gitmodules --get "submodule.one.$var" ||
+		return 1
+	done >actual &&
+	test_write_lines all one ./one >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'setup - initial commit' '
 	>t &&
 	git add t &&