expose module errors into metadata (#3752)

* expose module errors into metadata

* it checks

* Tests for error metadata

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* remove inherent errors from metadata

* bump version

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/support/src/error.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/srml/support/src/dispatch.rs

@@ -23,7 +23,7 @@ pub use std::fmt;
 pub use crate::codec::{Codec, EncodeLike, Decode, Encode, Input, Output, HasCompact, EncodeAsRef};
 pub use srml_metadata::{
 	FunctionMetadata, DecodeDifferent, DecodeDifferentArray, FunctionArgumentMetadata,
-	ModuleConstantMetadata, DefaultByte, DefaultByteGetter,
+	ModuleConstantMetadata, DefaultByte, DefaultByteGetter, ModuleErrorMetadata, ErrorMetadata
 };
 pub use sr_primitives::{
 	weights::{
@@ -1298,6 +1298,14 @@ macro_rules! decl_module {
 			{ $( $other_where_bounds )* }
 			$( $constants )*
 		}
+
+		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::ModuleErrorMetadata
+			for $mod_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
+		{
+			fn metadata() -> &'static [$crate::dispatch::ErrorMetadata] {
+				<$error_type as $crate::dispatch::ModuleErrorMetadata>::metadata()
+			}
+		}
 	}
 }
 

substrate/srml/support/src/error.rs

@@ -18,6 +18,7 @@
 
 #[doc(hidden)]
 pub use sr_primitives::traits::LookupError;
+pub use srml_metadata::{ModuleErrorMetadata, ErrorMetadata, DecodeDifferent};
 
 /// Declare an error type for a runtime module.
 ///
@@ -49,7 +50,7 @@ macro_rules! decl_error {
 		$(#[$attr:meta])*
 		pub enum $error:ident {
 			$(
-				$( #[$variant_attr:meta] )*
+				$( #[doc = $doc_attr:tt] )*
 				$name:ident
 			),*
 			$(,)?
@@ -62,7 +63,7 @@ macro_rules! decl_error {
 			Other(&'static str),
 			CannotLookup,
 			$(
-				$(#[$variant_attr])*
+				$( #[doc = $doc_attr] )*
 				$name
 			),*
 		}
@@ -115,6 +116,21 @@ macro_rules! decl_error {
 				$crate::dispatch::DispatchError::new(None, self.as_u8(), Some(self.as_str()))
 			}
 		}
+
+		impl $crate::error::ModuleErrorMetadata for $error {
+			fn metadata() -> &'static [$crate::error::ErrorMetadata] {
+				&[
+					$(
+						$crate::error::ErrorMetadata {
+							name: $crate::error::DecodeDifferent::Encode(stringify!($name)),
+							documentation: $crate::error::DecodeDifferent::Encode(&[
+								$( $doc_attr ),*
+							]),
+						}
+					),*
+				]
+			}
+		}
 	};
 	(@GENERATE_AS_U8
 		$self:ident

substrate/srml/support/src/metadata.rs

@@ -17,7 +17,7 @@
 pub use srml_metadata::{
 	DecodeDifferent, FnEncode, RuntimeMetadata, ModuleMetadata, RuntimeMetadataLastVersion,
 	DefaultByteGetter, RuntimeMetadataPrefixed, StorageEntryMetadata, StorageMetadata,
-	StorageEntryType, StorageEntryModifier, DefaultByte, StorageHasher
+	StorageEntryType, StorageEntryModifier, DefaultByte, StorageHasher, ModuleErrorMetadata
 };
 
 /// Implements the metadata support for the given runtime and all its modules.
@@ -96,6 +96,11 @@ macro_rules! __runtime_modules_to_metadata {
 					$crate::metadata::FnEncode(
 						$mod::$module::<$runtime $(, $mod::$instance )?>::module_constants_metadata
 					)
+				),
+				errors: $crate::metadata::DecodeDifferent::Encode(
+					$crate::metadata::FnEncode(
+						<$mod::$module::<$runtime $(, $mod::$instance )?> as $crate::metadata::ModuleErrorMetadata>::metadata
+					)
 				)
 			};
 			$( $rest )*
@@ -227,6 +232,7 @@ mod tests {
 	use srml_metadata::{
 		EventMetadata, StorageEntryModifier, StorageEntryType, FunctionMetadata, StorageEntryMetadata,
 		ModuleMetadata, RuntimeMetadataPrefixed, DefaultByte, ModuleConstantMetadata, DefaultByteGetter,
+		ErrorMetadata,
 	};
 	use codec::{Encode, Decode};
 	use crate::traits::Get;
@@ -278,7 +284,7 @@ mod tests {
 	}
 
 	mod event_module {
-		use crate::dispatch::Result;
+		use crate::dispatch::DispatchResult;
 
 		pub trait Trait {
 			type Origin;
@@ -296,7 +302,19 @@ mod tests {
 
 		decl_module! {
 			pub struct Module<T: Trait> for enum Call where origin: T::Origin {
-				fn aux_0(_origin) -> Result { unreachable!() }
+				type Error = Error;
+
+				fn aux_0(_origin) -> DispatchResult<Error> { unreachable!() }
+			}
+		}
+
+		crate::decl_error! {
+			pub enum Error {
+				/// Some user input error
+				UserInputError,
+				/// Something bad happened
+				/// this could be due to many reasons
+				BadThingHappened,
 			}
 		}
 	}
@@ -447,6 +465,7 @@ mod tests {
 						}
 					])
 				),
+				errors: DecodeDifferent::Encode(FnEncode(|| &[])),
 			},
 			ModuleMetadata {
 				name: DecodeDifferent::Encode("Module"),
@@ -469,6 +488,19 @@ mod tests {
 					])
 				)),
 				constants: DecodeDifferent::Encode(FnEncode(|| &[])),
+				errors: DecodeDifferent::Encode(FnEncode(|| &[
+					ErrorMetadata {
+						name: DecodeDifferent::Encode("UserInputError"),
+						documentation: DecodeDifferent::Encode(&[" Some user input error"]),
+					},
+					ErrorMetadata {
+						name: DecodeDifferent::Encode("BadThingHappened"),
+						documentation: DecodeDifferent::Encode(&[
+							" Something bad happened",
+							" this could be due to many reasons",
+						]),
+					},
+				])),
 			},
 			ModuleMetadata {
 				name: DecodeDifferent::Encode("Module2"),
@@ -505,6 +537,7 @@ mod tests {
 					])
 				)),
 				constants: DecodeDifferent::Encode(FnEncode(|| &[])),
+				errors: DecodeDifferent::Encode(FnEncode(|| &[])),
 			},
 		])
 	};