submodule: export sanitized GIT_CONFIG_PARAMETERS

Commit 14111fc4 (git: submodule honor -c credential.* from
command line, 2016-02-29) taught git-submodule.sh to save
the sanitized value of $GIT_CONFIG_PARAMETERS when clearing
the environment for a submodule. However, it failed to
export the result, meaning that it had no effect for any
sub-programs.

We didn't catch this in our initial tests because we checked
only the "clone" case, which does not go through the shell
script at all. Provoking "git submodule update" to do a
fetch demonstrates the bug.
Noticed-by: NLars Schneider <larsxschneider@gmail.com>
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -200,6 +200,7 @@ sanitize_submodule_env()
 	sanitized_config=$(git submodule--helper sanitize-config)
 	clear_local_git_env
 	GIT_CONFIG_PARAMETERS=$sanitized_config
+	export GIT_CONFIG_PARAMETERS
 }
 
 #

t/t5550-http-fetch-dumb.sh

@@ -112,6 +112,23 @@ test_expect_success 'cmdline credential config passes to submodule via clone' '
 	expect_askpass pass user@host
 '
 
+test_expect_success 'cmdline credential config passes submodule update' '
+	# advance the submodule HEAD so that a fetch is required
+	git commit --allow-empty -m foo &&
+	git push "$HTTPD_DOCUMENT_ROOT_PATH/auth/dumb/repo.git" HEAD &&
+	sha1=$(git rev-parse HEAD) &&
+	git -C super-clone update-index --cacheinfo 160000,$sha1,sub &&
+
+	set_askpass wrong pass@host &&
+	test_must_fail git -C super-clone submodule update &&
+
+	set_askpass wrong pass@host &&
+	git -C super-clone \
+	    -c "credential.$HTTPD_URL.username=user@host" \
+	    submodule update &&
+	expect_askpass pass user@host
+'
+
 test_expect_success 'fetch changes via http' '
 	echo content >>file &&
 	git commit -a -m two &&