Make decl_event! more flexible with the automatic naming of generic…

… parameters

The macro will now automatically derive the name of a generic parameter
from the trait type name, if no explicit name is given.

`where Balance = <T as Trait>::Balance` can be simplified to
`where <T as Trait>::Balance`.

srml/balances/src/lib.rs

@@ -137,9 +137,9 @@ decl_module! {
 
 decl_event!(
 	pub enum Event<T> where
-		AccountId = <T as system::Trait>::AccountId,
-		AccountIndex = <T as Trait>::AccountIndex,
-		Balance = <T as Trait>::Balance
+		<T as system::Trait>::AccountId,
+		<T as Trait>::AccountIndex,
+		<T as Trait>::Balance
 	{
 		/// A new account was created.
 		NewAccount(AccountId, AccountIndex, NewAccountOutcome),

srml/council/src/motions.rs

@@ -49,9 +49,7 @@ pub enum Origin {
 
 /// Event for this module.
 decl_event!(
-	pub enum Event<T>
-		where Hash = <T as system::Trait>::Hash, AccountId = <T as system::Trait>::AccountId
-	{
+	pub enum Event<T> where <T as system::Trait>::Hash, <T as system::Trait>::AccountId {
 		/// A motion (given hash) has been proposed (by given account) with a threshold (given u32).
 		Proposed(AccountId, ProposalIndex, Hash, u32),
 		/// A motion (given hash) has been voted on by given account, leaving

srml/council/src/seats.rs

@@ -156,7 +156,7 @@ decl_storage! {
 
 decl_event!(
 	/// An event in this module.
-	pub enum Event<T> where AccountId = <T as system::Trait>::AccountId {
+	pub enum Event<T> where <T as system::Trait>::AccountId {
 		/// reaped voter, reaper
 		VoterReaped(AccountId, AccountId),
 		/// slashed reaper

srml/council/src/voting.rs

@@ -55,7 +55,7 @@ decl_storage! {
 
 /// An event in this module.
 decl_event!(
-	pub enum Event<T> where Hash = <T as system::Trait>::Hash {
+	pub enum Event<T> where <T as system::Trait>::Hash {
 		/// A voting tally has happened for a referendum cancelation vote.
 		/// Last three are yes, no, abstain counts.
 		TallyCancelation(Hash, u32, u32, u32),

srml/democracy/src/lib.rs

@@ -110,10 +110,7 @@ decl_storage! {
 
 decl_event!(
 	/// An event in this module.
-	pub enum Event<T> where
-		Balance = <T as balances::Trait>::Balance,
-		AccountId = <T as system::Trait>::AccountId
-	{
+	pub enum Event<T> where <T as balances::Trait>::Balance, <T as system::Trait>::AccountId {
 		Tabled(PropIndex, Balance, Vec<AccountId>),
 		Started(ReferendumIndex, VoteThreshold),
 		Passed(ReferendumIndex),

srml/session/src/lib.rs

@@ -84,7 +84,7 @@ decl_module! {
 
 /// An event in this module.
 decl_event!(
-	pub enum Event<T> where BlockNumber = <T as system::Trait>::BlockNumber {
+	pub enum Event<T> where <T as system::Trait>::BlockNumber {
 		/// New session has happened. Note that the argument is the session index, not the block
 		/// number as the type might suggest.
 		NewSession(BlockNumber),

srml/staking/src/lib.rs

@@ -120,10 +120,7 @@ decl_module! {
 
 /// An event in this module.
 decl_event!(
-	pub enum Event<T> where
-		Balance = <T as balances::Trait>::Balance,
-		AccountId = <T as system::Trait>::AccountId
-	{
+	pub enum Event<T> where <T as balances::Trait>::Balance, <T as system::Trait>::AccountId {
 		/// All validators have been rewarded by the given balance.
 		Reward(Balance),
 		/// One validator (and their nominators) has been given a offline-warning (they're still

srml/support/src/event.rs

@@ -14,60 +14,217 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
-/// Implement an `Event`/`RawEvent` for a module.
+/// Implement the `Event` for a module.
+///
+/// # Simple Event Example:
+///
+/// ```rust
+/// #[macro_use]
+/// extern crate substrate_runtime_support;
+/// extern crate substrate_codec as codec;
+/// #[macro_use]
+/// extern crate substrate_codec_derive;
+/// #[macro_use]
+/// extern crate serde_derive;
+///
+/// decl_event!(
+///	   pub enum Event {
+///       Success,
+///       Failure(String),
+///    }
+/// );
+///# fn main() {}
+/// ```
+///
+/// # Generic Event Example:
+///
+/// ```rust
+/// #[macro_use]
+/// extern crate substrate_runtime_support;
+/// extern crate substrate_codec as codec;
+/// #[macro_use]
+/// extern crate substrate_codec_derive;
+/// #[macro_use]
+/// extern crate serde_derive;
+///
+/// trait Trait {
+///     type Balance;
+///     type Token;
+/// }
+///
+/// mod event1 {
+///     // Event that specifies the generic parameter explicitly (`Balance`).
+///     decl_event!(
+///	       pub enum Event<T> where Balance = <T as super::Trait>::Balance {
+///           Message(Balance),
+///        }
+///     );
+/// }
+///
+/// mod event2 {
+///     // Event that uses the generic parameter `Balance`.
+///     // If no name for the generic parameter is speciefied explicitly,
+///     // the name will be taken from the type name of the trait.
+///     decl_event!(
+///	       pub enum Event<T> where <T as super::Trait>::Balance {
+///           Message(Balance),
+///        }
+///     );
+/// }
+///
+/// mod event3 {
+///     // And we even support declaring multiple generic parameters!
+///     decl_event!(
+///	       pub enum Event<T> where <T as super::Trait>::Balance, <T as super::Trait>::Token {
+///           Message(Balance, Token),
+///        }
+///     );
+/// }
+///# fn main() {}
+/// ```
+///
+/// The syntax for generic events requires the `where`.
 #[macro_export]
 macro_rules! decl_event {
 	(
 		$(#[$attr:meta])*
-		pub enum Event<$evt_generic_param:ident>
-			where $($generic_param:ident = <$generic:ident as $trait:path>::$trait_type:ident),*
+		pub enum Event<$evt_generic_param:ident> where
+			$( $( $generic_rename:ident = )* <$generic:ident as $trait:path>::$trait_type:ident ),*
 		{
 			$(
 				$events:tt
 			)*
 		}
 	) => {
-		pub type Event<$evt_generic_param> = RawEvent<$( <$generic as $trait>::$trait_type ),*>;
+		__decl_generic_event!(
+			$( #[ $attr ] )*;
+			$evt_generic_param;
+			$( $( $generic_rename = )* <$generic as $trait>::$trait_type ),*;
+			Events { $( $events )* };
+		);
+	};
+	(
+		$(#[$attr:meta])*
+		pub enum Event {
+			$(
+				$events:tt
+			)*
+		}
+	) => {
 		// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
 		#[derive(Clone, PartialEq, Eq, Encode, Decode)]
 		#[cfg_attr(feature = "std", derive(Debug, Serialize, Deserialize))]
 		$(#[$attr])*
-		pub enum RawEvent<$( $generic_param ),*> {
+		pub enum Event {
 			$(
 				$events
 			)*
 		}
-		impl<$( $generic_param ),*> From<RawEvent<$( $generic_param ),*>> for () {
-			fn from(_: RawEvent<$( $generic_param ),*>) -> () { () }
+		impl From<Event> for () {
+			fn from(_: Event) -> () { () }
 		}
-		impl<$( $generic_param ),*> RawEvent<$( $generic_param ),*> {
+		impl Event {
 			#[allow(dead_code)]
 			pub fn event_json_metadata() -> &'static str {
 				concat!("{", __events_to_json!(""; $( $events )* ), " }")
 			}
 		}
+	}
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! __decl_generic_event {
+	(
+		$(#[$attr:meta])*;
+		$event_generic_param:ident;
+		$generic_rename:ident = <$generic:ident as $trait:path>::$trait_type:ident
+			$(, $( $rest_gen_rename:ident = )* <$rest_gen:ident as $rest_trait:path>::$rest_trait_type:ident )*;
+		Events { $( $events:tt )* };
+	) => {
+		__decl_generic_event!(
+			$( #[ $attr ] )*;
+			$event_generic_param;
+			$( $( $rest_gen_rename = )* <$rest_gen as $rest_trait>::$rest_trait_type ),*;
+			Events { $( $events )* };
+			$generic_rename;
+			<$generic as $trait>::$trait_type;
+		);
 	};
 	(
-		$(#[$attr:meta])*
-		pub enum Event {
-			$(
-				$events:tt
-			)*
-		}
+		$(#[$attr:meta])*;
+		$event_generic_param:ident;
+		$generic_rename:ident = <$generic:ident as $trait:path>::$trait_type:ident
+			$(, $( $rest_gen_rename:ident = )* <$rest_gen:ident as $rest_trait:path>::$rest_trait_type:ident )*;
+		Events { $( $events:tt )* };
+		$( $parsed_generic_params:ident ),*;
+		$( <$parsed_generic:ident as $parsed_trait:path>::$parsed_trait_type:ident ),*;
+	) => {
+		__decl_generic_event!(
+			$( #[ $attr ] )*;
+			$event_generic_param;
+			$( $( $rest_gen_rename = )* <$rest_gen as $rest_trait>::$rest_trait_type ),*;
+			Events { $( $events )* };
+			$( $parsed_generic_params ),*, $generic_rename;
+			$( <$parsed_generic as $parsed_trait>::$parsed_trait_type ),*, <$generic as $trait>::$trait_type;
+		);
+	};
+	(
+		$(#[$attr:meta])*;
+		$event_generic_param:ident;
+		<$generic:ident as $trait:path>::$trait_type:ident
+			$(, $( $rest_gen_rename:ident = )* <$rest_gen:ident as $rest_trait:path>::$rest_trait_type:ident )*;
+		Events { $( $events:tt )* };
+	) => {
+		__decl_generic_event!(
+			$( #[ $attr ] )*;
+			$event_generic_param;
+			$( $( $rest_gen_rename = )* <$rest_gen as $rest_trait>::$rest_trait_type ),*;
+			Events { $( $events )* };
+			$trait_type;
+			<$generic as $trait>::$trait_type;
+		);
+	};
+	(
+		$(#[$attr:meta])*;
+		$event_generic_param:ident;
+		<$generic:ident as $trait:path>::$trait_type:ident
+			$(, $( $rest_gen_rename:ident = )* <$rest_gen:ident as $rest_trait:path>::$rest_trait_type:ident )*;
+		Events { $( $events:tt )* };
+		$( $parsed_generic_params:ident ),*;
+		$( <$parsed_generic:ident as $parsed_trait:path>::$parsed_trait_type:ident ),*;
+	) => {
+		__decl_generic_event!(
+			$( #[ $attr ] )*;
+			$event_generic_param;
+			$( $( $rest_gen_rename = )* <$rest_gen as $rest_trait>::$rest_trait_type ),*;
+			Events { $( $events )* };
+			$( $parsed_generic_params ),*, $trait_type;
+			$( <$parsed_generic as $parsed_trait>::$parsed_trait_type ),*, <$generic as $trait>::$trait_type;
+		);
+	};
+	(
+		$(#[$attr:meta])*;
+		$event_generic_param:ident;
+		;
+		Events { $( $events:tt )* };
+		$( $generic_param:ident ),*;
+		$( <$generic:ident as $trait:path>::$trait_type:ident ),*;
 	) => {
+		pub type Event<$event_generic_param> = RawEvent<$( <$generic as $trait>::$trait_type ),*>;
 		// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
 		#[derive(Clone, PartialEq, Eq, Encode, Decode)]
 		#[cfg_attr(feature = "std", derive(Debug, Serialize, Deserialize))]
 		$(#[$attr])*
-		pub enum Event {
+		pub enum RawEvent<$( $generic_param ),*> {
 			$(
 				$events
 			)*
 		}
-		impl From<Event> for () {
-			fn from(_: Event) -> () { () }
+		impl<$( $generic_param ),*> From<RawEvent<$( $generic_param ),*>> for () {
+			fn from(_: RawEvent<$( $generic_param ),*>) -> () { () }
 		}
-		impl Event {
+		impl<$( $generic_param ),*> RawEvent<$( $generic_param ),*> {
 			#[allow(dead_code)]
 			pub fn event_json_metadata() -> &'static str {
 				concat!("{", __events_to_json!(""; $( $events )* ), " }")
@@ -203,10 +360,11 @@ mod tests {
 		}
 
 		decl_event!(
-			pub enum Event<T> where Balance = <T as Trait>::Balance
+			/// Event without renaming the generic parameter `Balance` and `Origin`.
+			pub enum Event<T> where <T as Trait>::Balance, <T as Trait>::Origin
 			{
 				/// Hi, I am a comment.
-				TestEvent(Balance),
+				TestEvent(Balance, Origin),
 				/// Dog
 				EventWithoutParams,
 			}
@@ -224,9 +382,13 @@ mod tests {
 		}
 
 		decl_event!(
-			pub enum Event<T> where Balance = <T as Trait>::Balance
+			/// Event with renamed generic parameter
+			pub enum Event<T> where
+				BalanceRenamed = <T as Trait>::Balance,
+				OriginRenamed = <T as Trait>::Origin
 			{
-				TestEvent(Balance),
+				TestEvent(BalanceRenamed),
+				TestOrigin(OriginRenamed),
 			}
 		);
 	}
@@ -260,12 +422,19 @@ mod tests {
 			("event_module",
 				concat!(
 					"{",
-					r#" "TestEvent": { "params": [ "Balance" ], "description": [ " Hi, I am a comment." ] },"#,
+					r#" "TestEvent": { "params": [ "Balance", "Origin" ], "description": [ " Hi, I am a comment." ] },"#,
 					r#" "EventWithoutParams": { "params": null, "description": [ " Dog" ] }"#,
 					" }"
 				)
 			),
-			("event_module2", r#"{ "TestEvent": { "params": [ "Balance" ], "description": [ ] } }"#),
+			("event_module2",
+				concat!(
+					"{",
+					r#" "TestEvent": { "params": [ "BalanceRenamed" ], "description": [ ] },"#,
+					r#" "TestOrigin": { "params": [ "OriginRenamed" ], "description": [ ] }"#,
+					" }"
+				)
+			),
 		]
 	);
 

srml/support/src/metadata.rs

@@ -151,7 +151,7 @@ mod tests {
 		}
 
 		decl_event!(
-			pub enum Event<T> where Balance = <T as Trait>::Balance
+			pub enum Event<T> where <T as Trait>::Balance
 			{
 				/// Hi, I am a comment.
 				TestEvent(Balance),
@@ -178,7 +178,7 @@ mod tests {
 		}
 
 		decl_event!(
-			pub enum Event<T> where Balance = <T as Trait>::Balance
+			pub enum Event<T> where <T as Trait>::Balance
 			{
 				TestEvent(Balance),
 			}

srml/treasury/src/lib.rs

@@ -136,10 +136,7 @@ decl_storage! {
 
 /// An event in this module.
 decl_event!(
-	pub enum Event<T> where
-		Balance = <T as balances::Trait>::Balance,
-		AccountId = <T as system::Trait>::AccountId
-	{
+	pub enum Event<T> where <T as balances::Trait>::Balance, <T as system::Trait>::AccountId {
 		/// New proposal.
 		Proposed(ProposalIndex),
 		/// We have ended a spend period and will now allocate funds.