Make decl_error! errors usable (#4449)

* Make `decl_error!` errors usable

This pr implements support for returning errors of different pallets in
a pallet. These errors need to be declared with `decl_error!`.

The pr changes the following:

- Each dispatchable function now returns a `DispatchResult` which is an
alias for `Result<(), DispatchError>`.
- `DispatchError` is an enum that has 4 variants:
  - `Other`: For storing string error messages
  - `CannotLookup`: Variant that is returned when something returns a
  `sp_runtime::LookupError`
  - `BadOrigin`: Variant that is returned for any kind of bad origin
  - `Module`: The error of a specific module. Contains the `index`,
  `error` and the `message`. The index is the index of the module in
  `construct_runtime!`. `error` is the index of the error in the error
  enum declared by `decl_error!`. `message` is the message to the error
  variant (this will not be encoded).
- `construct_runtime!` now creates a new struct `ModuleToIndex`. This
struct implements the trait `ModuleToIndex`.
- `frame_system::Trait` has a new associated type: `ModuleToIndex` that
expects the `ModuleToIndex` generated by `construct_runtime!`.
- All error strings returned in any module are being converted now to `DispatchError`.
- `BadOrigin` is the default error returned by any type that implements `EnsureOrigin`.

* Fix frame system benchmarks

substrate/frame/authorship/src/lib.rs

@@ -184,12 +184,12 @@ decl_module! {
 
 		/// Provide a set of uncles.
 		#[weight = SimpleDispatchInfo::FixedOperational(10_000)]
-		fn set_uncles(origin, new_uncles: Vec<T::Header>) -> dispatch::Result {
+		fn set_uncles(origin, new_uncles: Vec<T::Header>) -> dispatch::DispatchResult {
 			ensure_none(origin)?;
 			ensure!(new_uncles.len() <= MAX_UNCLES, "Too many uncles");
 
 			if <Self as Store>::DidSetUncles::get() {
-				return Err("Uncles already set in block.");
+				Err("Uncles already set in block.")?
 			}
 			<Self as Store>::DidSetUncles::put(true);
 
@@ -219,7 +219,7 @@ impl<T: Trait> Module<T> {
 		}
 	}
 
-	fn verify_and_import_uncles(new_uncles: Vec<T::Header>) -> dispatch::Result {
+	fn verify_and_import_uncles(new_uncles: Vec<T::Header>) -> dispatch::DispatchResult {
 		let now = <frame_system::Module<T>>::block_number();
 
 		let mut uncles = <Self as Store>::Uncles::get();
@@ -408,6 +408,7 @@ mod tests {
 		type AvailableBlockRatio = AvailableBlockRatio;
 		type MaximumBlockLength = MaximumBlockLength;
 		type Version = ();
+		type ModuleToIndex = ();
 	}
 
 	parameter_types! {
@@ -565,7 +566,7 @@ mod tests {
 				);
 				assert_eq!(
 					Authorship::verify_and_import_uncles(vec![uncle_a.clone(), uncle_a.clone()]),
-					Err("uncle already included"),
+					Err("uncle already included".into()),
 				);
 			}
 
@@ -580,7 +581,7 @@ mod tests {
 
 				assert_eq!(
 					Authorship::verify_and_import_uncles(vec![uncle_a.clone()]),
-					Err("uncle already included"),
+					Err("uncle already included".into()),
 				);
 			}
 
@@ -590,7 +591,7 @@ mod tests {
 
 				assert_eq!(
 					Authorship::verify_and_import_uncles(vec![uncle_clone]),
-					Err("uncle already included"),
+					Err("uncle already included".into()),
 				);
 			}
 
@@ -599,7 +600,7 @@ mod tests {
 				let unsealed = create_header(3, canon_chain.canon_hash(2), [2; 32].into());
 				assert_eq!(
 					Authorship::verify_and_import_uncles(vec![unsealed]),
-					Err("no author"),
+					Err("no author".into()),
 				);
 			}
 
@@ -614,7 +615,7 @@ mod tests {
 
 				assert_eq!(
 					Authorship::verify_and_import_uncles(vec![gen_2]),
-					Err("uncle not recent enough to be included"),
+					Err("uncle not recent enough to be included".into()),
 				);
 			}