Fixes compile error and warning

substrate/runtime-support/src/metadata.rs

@@ -14,7 +14,9 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
-use codec::{Encode, Decode, Output, Input};
+use codec::{Encode, Output};
+#[cfg(feature = "std")]
+use codec::{Decode, Input};
 use alloc;
 
 /// Make Box available on `std` and `no_std`.

substrate/test-runtime/src/lib.rs

@@ -134,9 +134,11 @@ pub mod api {
 	use system;
 	impl_stubs!(
 		version => |()| super::version(),
-		json_metadata => |()| vec![
-			::runtime_support::metadata::JSONMetadata::Events { events: r#""events""# }
-		],
+		json_metadata => |()| {
+			let mut vec = ::runtime_support::metadata::Vec::new();
+			vec.push(::runtime_support::metadata::JSONMetadata::Events { events: r#""events""# });
+			vec
+		},
 		authorities => |()| system::authorities(),
 		initialise_block => |header| system::initialise_block(header),
 		execute_block => |block| system::execute_block(block),