Improve error handling in proc-macros, handle DispatchError etc. (#123)

* Improve error handling.

* Fix build.

* Handle runtime errors.

* Add runtime trait for better type inference.

* Use runtime trait part 1.

* wip

* Add support for sudo.

* Finish error handling.

* Fix tests.

* Fix clippy warnings.

src/frame/sudo.rs

@@ -0,0 +1,78 @@
+// Copyright 2019-2020 Parity Technologies (UK) Ltd.
+// This file is part of substrate-subxt.
+//
+// subxt is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// subxt is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with substrate-subxt.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Implements support for the frame_sudo module.
+
+use crate::{
+    frame::system::{
+        System,
+        SystemEventsDecoder,
+    },
+    Encoded,
+};
+use codec::Encode;
+use core::marker::PhantomData;
+
+/// The subset of the `frame_sudo::Trait` that a client must implement.
+#[module]
+pub trait Sudo: System {}
+
+/// Execute a transaction with sudo permissions.
+#[derive(Clone, Debug, Eq, PartialEq, Call, Encode)]
+pub struct SudoCall<'a, T: Sudo> {
+    /// Runtime marker.
+    pub _runtime: PhantomData<T>,
+    /// Encoded transaction.
+    pub call: &'a Encoded,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{
+        error::Error,
+        frame::balances::TransferCall,
+        signer::PairSigner,
+        tests::{
+            test_client,
+            TestRuntime,
+        },
+    };
+    use sp_keyring::AccountKeyring;
+
+    #[async_std::test]
+    async fn test_sudo() {
+        env_logger::try_init().ok();
+        let alice = PairSigner::<TestRuntime, _>::new(AccountKeyring::Alice.pair());
+        let (client, _) = test_client().await;
+
+        let call = client
+            .encode(TransferCall {
+                to: &AccountKeyring::Bob.to_account_id(),
+                amount: 10_000,
+            })
+            .unwrap();
+
+        let res = client.sudo_and_watch(&alice, &call).await;
+        assert!(
+            if let Err(Error::BadOrigin) = res {
+                true
+            } else {
+                false
+            }
+        );
+    }
+}