Remove bounds on Config trait that aren't strictly necessary (parityt…

…ech#389)

* Use Derivative to skip bounds on T when they aren't necessary, and remove unnecessary bounds on Config

* loosen a couple more derive bounds

* Use PhantomDataSendSync to avoid accidentally removing Send+Sync bounds

Cargo.toml

@@ -39,6 +39,7 @@ sp-runtime = { git = "https://github.com/paritytech/substrate/", branch = "maste
 sp-version = { package = "sp-version", git = "https://github.com/paritytech/substrate/", branch = "master" }
 
 frame-metadata = "14.0.0"
+derivative = "2.2.0"
 
 [dev-dependencies]
 sp-arithmetic = { git = "https://github.com/paritytech/substrate/", branch = "master", default-features = false }

src/client.rs

@@ -40,6 +40,7 @@ use crate::{
     Config,
     Metadata,
 };
+use derivative::Derivative;
 use std::sync::Arc;
 
 /// ClientBuilder for constructing a Client.
@@ -111,7 +112,8 @@ impl ClientBuilder {
 }
 
 /// Client to interface with a substrate node.
-#[derive(Clone)]
+#[derive(Derivative)]
+#[derivative(Clone(bound = ""))]
 pub struct Client<T: Config> {
     rpc: Rpc<T>,
     genesis_hash: T::Hash,

src/config.rs

@@ -32,7 +32,10 @@ use sp_runtime::traits::{
 };
 
 /// Runtime types.
-pub trait Config: Clone + Default + Sized + Send + Sync + 'static {
+// Note: the 'static bound isn't strictly required, but currently deriving TypeInfo
+// automatically applies a 'static bound to all generic types (including this one),
+// and so until that is resolved, we'll keep the (easy to satisfy) constraint here.
+pub trait Config: 'static {
     /// Account index (aka nonce) type. This stores the number of previous
     /// transactions associated with a sender account.
     type Index: Parameter + Member + Default + AtLeast32Bit + Copy + scale_info::TypeInfo;
@@ -83,8 +86,9 @@ pub trait Parameter: Codec + EncodeLike + Clone + Eq + Debug {}
 impl<T> Parameter for T where T: Codec + EncodeLike + Clone + Eq + Debug {}
 
 /// Default set of commonly used types by Substrate runtimes.
-#[derive(Clone, Debug, Default, Eq, PartialEq)]
-pub struct DefaultConfig;
+// Note: We only use this at the type level, so it should be impossible to
+// create an instance of it.
+pub enum DefaultConfig {}
 
 impl Config for DefaultConfig {
     type Index = u32;

src/events.rs

@@ -14,16 +14,6 @@
 // You should have received a copy of the GNU General Public License
 // along with subxt.  If not, see <http://www.gnu.org/licenses/>.
 
-use codec::{
-    Codec,
-    Compact,
-    Decode,
-    Encode,
-    Error as CodecError,
-    Input,
-};
-use std::marker::PhantomData;
-
 use crate::{
     metadata::{
         EventMetadata,
@@ -33,8 +23,18 @@ use crate::{
     Error,
     Event,
     Metadata,
+    PhantomDataSendSync,
     Phase,
 };
+use codec::{
+    Codec,
+    Compact,
+    Decode,
+    Encode,
+    Error as CodecError,
+    Input,
+};
+use derivative::Derivative;
 use scale_info::{
     TypeDef,
     TypeDefPrimitive,
@@ -69,16 +69,14 @@ impl RawEvent {
 }
 
 /// Events decoder.
-#[derive(Debug, Clone)]
-pub struct EventsDecoder<T> {
+#[derive(Derivative)]
+#[derivative(Clone(bound = ""), Debug(bound = ""))]
+pub struct EventsDecoder<T: Config> {
     metadata: Metadata,
-    marker: PhantomData<T>,
+    marker: PhantomDataSendSync<T>,
 }
 
-impl<T> EventsDecoder<T>
-where
-    T: Config,
-{
+impl<T: Config> EventsDecoder<T> {
     /// Creates a new `EventsDecoder`.
     pub fn new(metadata: Metadata) -> Self {
         Self {