Allow where bounds on decl_module! and decl_storage! (#3000)

* Introduces a `where` bound to `decl_macro!` and `decl_storage!`

* More fixes

* Adds documentation

substrate/srml/support/procedural/src/lib.rs

@@ -139,6 +139,14 @@ use proc_macro::TokenStream;
 /// Accessing the structure no requires the instance as generic parameter:
 /// * `Foo::<I>` if the value type is not generic
 /// * `Foo::<T, I>` if the value type is generic
+///
+/// ## Where clause
+///
+/// This macro supports a where clause which will be replicated to all generated types.
+///
+/// ```nocompile
+/// trait Store for Module<T: Trait> as Example where T::AccountId: std::fmt::Display {}
+/// ```
 #[proc_macro]
 pub fn decl_storage(input: TokenStream) -> TokenStream {
 	storage::transformation::decl_storage_impl(input)

substrate/srml/support/procedural/src/storage/impls.rs

@@ -47,6 +47,7 @@ pub(crate) struct Impls<'a, I: Iterator<Item=syn::Meta>> {
 	pub cratename: &'a syn::Ident,
 	pub name: &'a syn::Ident,
 	pub attrs: I,
+	pub where_clause: &'a Option<syn::WhereClause>,
 }
 
 impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
@@ -62,6 +63,7 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			prefix,
 			name,
 			attrs,
+			where_clause,
 			..
 		} = self;
 		let DeclStorageTypeInfos { typ, value_type, is_option, .. } = type_infos;
@@ -94,19 +96,21 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			quote!{ #prefix.as_bytes() }
 		};
 
-		let (struct_trait, impl_trait, trait_and_instance) = if ext::type_contains_ident(
+		let (struct_trait, impl_trait, trait_and_instance, where_clause) = if ext::type_contains_ident(
 			value_type, traitinstance
 		) {
 			(
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable #equal_default_instance),
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable),
 				quote!(#traitinstance, #instance),
+				where_clause.clone(),
 			)
 		} else {
 			(
 				quote!(#instance #bound_instantiable #equal_default_instance),
 				quote!(#instance #bound_instantiable),
-				quote!(#instance)
+				quote!(#instance),
+				None,
 			)
 		};
 
@@ -115,10 +119,10 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			#( #[ #attrs ] )*
 			#visibility struct #name<#struct_trait>(
 				#scrate::rstd::marker::PhantomData<(#trait_and_instance)>
-			);
+			) #where_clause;
 
 			impl<#impl_trait> #scrate::storage::hashed::generator::StorageValue<#typ>
-				for #name<#trait_and_instance>
+				for #name<#trait_and_instance> #where_clause
 			{
 				type Query = #value_type;
 
@@ -167,6 +171,7 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			prefix,
 			name,
 			attrs,
+			where_clause,
 			..
 		} = self;
 		let DeclStorageTypeInfos { typ, value_type, is_option, .. } = type_infos;
@@ -201,19 +206,22 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			quote!{ #prefix.as_bytes() }
 		};
 
-		let (struct_trait, impl_trait, trait_and_instance) = if ext::type_contains_ident(value_type, traitinstance)
-			|| ext::type_contains_ident(kty, traitinstance)
-		{
+		let trait_required = ext::type_contains_ident(value_type, traitinstance)
+			|| ext::type_contains_ident(kty, traitinstance);
+
+		let (struct_trait, impl_trait, trait_and_instance, where_clause) = if trait_required {
 			(
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable #equal_default_instance),
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable),
 				quote!(#traitinstance, #instance),
+				where_clause.clone(),
 			)
 		} else {
 			(
 				quote!(#instance #bound_instantiable #equal_default_instance),
 				quote!(#instance #bound_instantiable),
-				quote!(#instance)
+				quote!(#instance),
+				None,
 			)
 		};
 
@@ -222,10 +230,10 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			#( #[ #attrs ] )*
 			#visibility struct #name<#struct_trait>(
 				#scrate::rstd::marker::PhantomData<(#trait_and_instance)>
-			);
+			) #where_clause;
 
-			impl<#impl_trait>
-				#scrate::storage::hashed::generator::StorageMap<#kty, #typ> for #name<#trait_and_instance>
+			impl<#impl_trait> #scrate::storage::hashed::generator::StorageMap<#kty, #typ>
+				for #name<#trait_and_instance> #where_clause
 			{
 				type Query = #value_type;
 
@@ -270,7 +278,7 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			}
 
 			impl<#impl_trait> #scrate::storage::hashed::generator::AppendableStorageMap<#kty, #typ>
-				for #name<#trait_and_instance>
+				for #name<#trait_and_instance> #where_clause
 			{}
 		}
 	}
@@ -287,6 +295,7 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			prefix,
 			name,
 			attrs,
+			where_clause,
 			..
 		} = self;
 
@@ -298,7 +307,9 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 		} = instance_opts;
 
 		let final_prefix = if let Some(instance) = instance {
-			let const_name = syn::Ident::new(&format!("{}{}", PREFIX_FOR, name.to_string()), proc_macro2::Span::call_site());
+			let const_name = Ident::new(
+				&format!("{}{}", PREFIX_FOR, name.to_string()), proc_macro2::Span::call_site()
+			);
 			quote!{ #instance::#const_name.as_bytes() }
 		} else {
 			quote!{ #prefix.as_bytes() }
@@ -306,7 +317,9 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 
 		// make sure to use different prefix for head and elements.
 		let final_head_key = if let Some(instance) = instance {
-			let const_name = syn::Ident::new(&format!("{}{}", HEAD_KEY_FOR, name.to_string()), proc_macro2::Span::call_site());
+			let const_name = Ident::new(
+				&format!("{}{}", HEAD_KEY_FOR, name.to_string()), proc_macro2::Span::call_site()
+			);
 			quote!{ #instance::#const_name.as_bytes() }
 		} else {
 			let final_head_key = format!("head of {}", prefix);
@@ -316,8 +329,10 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 		let DeclStorageTypeInfos { typ, value_type, is_option, .. } = type_infos;
 		let option_simple_1 = option_unwrap(is_option);
 		let name_lowercase = name.to_string().to_lowercase();
-		let inner_module = syn::Ident::new(&format!("__linked_map_details_for_{}_do_not_use", name_lowercase), name.span());
-		let linkage = syn::Ident::new(&format!("__LinkageFor{}DoNotUse", name), name.span());
+		let inner_module = Ident::new(
+			&format!("__linked_map_details_for_{}_do_not_use", name_lowercase), name.span()
+		);
+		let linkage = Ident::new(&format!("__LinkageFor{}DoNotUse", name), name.span());
 		let phantom_data = quote! { #scrate::rstd::marker::PhantomData };
 		let as_map = quote!{ <Self as #scrate::storage::hashed::generator::StorageMap<#kty, #typ>> };
 		let put_or_insert = quote! {
@@ -337,23 +352,35 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			}
 		};
 
-		let (struct_trait, impl_trait, trait_and_instance, trait_lifetime) = if ext::type_contains_ident(
-			value_type,
-			traitinstance
-		) || ext::type_contains_ident(kty, traitinstance)
-		{
+		let trait_required = ext::type_contains_ident(value_type, traitinstance)
+			|| ext::type_contains_ident(kty, traitinstance);
+
+		let (struct_trait, impl_trait, trait_and_instance) = if trait_required {
 			(
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable #equal_default_instance),
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable),
 				quote!(#traitinstance, #instance),
-				quote!(#traitinstance: 'static),
 			)
 		} else {
 			(
 				quote!(#instance #bound_instantiable #equal_default_instance),
 				quote!(#instance #bound_instantiable),
 				quote!(#instance),
-				quote!()
+			)
+		};
+
+		let (where_clause, trait_where_clause) = if trait_required {
+			(
+				where_clause.clone(),
+				where_clause.clone().map(|mut wc| {
+					wc.predicates.push(syn::parse_quote!(#traitinstance: 'static));
+					wc
+				}).or_else(|| syn::parse_quote!(where #traitinstance: 'static)),
+			)
+		} else {
+			(
+				None,
+				None,
 			)
 		};
 
@@ -390,8 +417,8 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 					pub _data: #phantom_data<V>,
 				}
 
-				impl<'a, S: #scrate::HashedStorage<#scrate::#hasher>, #impl_trait>
-					Iterator for Enumerator<'a, S, #kty, (#typ, #trait_and_instance)>
+				impl<'a, S: #scrate::HashedStorage<#scrate::#hasher>, #impl_trait> Iterator
+					for Enumerator<'a, S, #kty, (#typ, #trait_and_instance)> #where_clause
 				{
 					type Item = (#kty, #typ);
 
@@ -442,7 +469,9 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			#( #[ #attrs ] )*
 			#visibility struct #name<#struct_trait>(#phantom_data<(#trait_and_instance)>);
 
-			impl<#impl_trait> self::#inner_module::Utils<#trait_and_instance> for #name<#trait_and_instance> {
+			impl<#impl_trait> self::#inner_module::Utils<#trait_and_instance>
+				for #name<#trait_and_instance> #where_clause
+			{
 				fn remove_linkage<S: #scrate::HashedStorage<#scrate::#hasher>>(
 					linkage: self::#inner_module::Linkage<#kty>,
 					storage: &mut S,
@@ -529,8 +558,8 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 
 			#structure
 
-			impl<#impl_trait>
-				#scrate::storage::hashed::generator::StorageMap<#kty, #typ> for #name<#trait_and_instance>
+			impl<#impl_trait> #scrate::storage::hashed::generator::StorageMap<#kty, #typ>
+				for #name<#trait_and_instance> #where_clause
 			{
 				type Query = #value_type;
 
@@ -605,10 +634,8 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 				}
 			}
 
-			impl<#impl_trait>
-				#scrate::storage::hashed::generator::EnumerableStorageMap<#kty, #typ> for #name<#trait_and_instance>
-				where
-					#trait_lifetime
+			impl<#impl_trait> #scrate::storage::hashed::generator::EnumerableStorageMap<#kty, #typ>
+				for #name<#trait_and_instance> #trait_where_clause
 			{
 				fn head<S: #scrate::HashedStorage<#scrate::#hasher>>(storage: &S) -> Option<#kty> {
 					use self::#inner_module::Utils;
@@ -654,13 +681,16 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			name,
 			attrs,
 			instance_opts,
+			where_clause,
 			..
 		} = self;
 
 		let DeclStorageTypeInfos { typ, value_type, is_option, .. } = type_infos;
 		let option_simple_1 = option_unwrap(is_option);
 
-		let as_double_map = quote!{ <Self as #scrate::storage::unhashed::generator::StorageDoubleMap<#k1ty, #k2ty, #typ>> };
+		let as_double_map = quote!{
+			<Self as #scrate::storage::unhashed::generator::StorageDoubleMap<#k1ty, #k2ty, #typ>>
+		};
 
 		let mutate_impl = if !is_option {
 			quote!{
@@ -683,26 +713,30 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 		} = instance_opts;
 
 		let final_prefix = if let Some(instance) = instance {
-			let const_name = syn::Ident::new(&format!("{}{}", PREFIX_FOR, name.to_string()), proc_macro2::Span::call_site());
+			let const_name = Ident::new(
+				&format!("{}{}", PREFIX_FOR, name.to_string()), proc_macro2::Span::call_site()
+			);
 			quote!{ #instance::#const_name.as_bytes() }
 		} else {
 			quote!{ #prefix.as_bytes() }
 		};
 
-		let (struct_trait, impl_trait, trait_and_instance) = if ext::type_contains_ident(value_type, traitinstance)
-			|| ext::type_contains_ident(k1ty, traitinstance)
-			|| ext::type_contains_ident(k2ty, traitinstance)
+		let (struct_trait, impl_trait, trait_and_instance, where_clause) = if ext::type_contains_ident(
+			value_type, traitinstance
+		) || ext::type_contains_ident(k1ty, traitinstance) || ext::type_contains_ident(k2ty, traitinstance)
 		{
 			(
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable #equal_default_instance),
 				quote!(#traitinstance: #traittype, #instance #bound_instantiable),
 				quote!(#traitinstance, #instance),
+				where_clause.clone(),
 			)
 		} else {
 			(
 				quote!(#instance #bound_instantiable #equal_default_instance),
 				quote!(#instance #bound_instantiable),
-				quote!(#instance)
+				quote!(#instance),
+				None,
 			)
 		};
 
@@ -712,8 +746,8 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 			#visibility struct #name<#struct_trait>
 				(#scrate::rstd::marker::PhantomData<(#trait_and_instance)>);
 
-			impl<#impl_trait>
-				#scrate::storage::unhashed::generator::StorageDoubleMap<#k1ty, #k2ty, #typ> for #name<#trait_and_instance>
+			impl<#impl_trait> #scrate::storage::unhashed::generator::StorageDoubleMap<#k1ty, #k2ty, #typ>
+				for #name<#trait_and_instance> #where_clause
 			{
 				type Query = #value_type;
 

substrate/srml/support/procedural/src/storage/mod.rs

@@ -65,6 +65,7 @@ struct StorageDefinition {
 	pub mod_gt_token: Token![>],
 	pub as_token: Token![as],
 	pub crate_ident: Ident,
+	pub where_clause: Option<syn::WhereClause>,
 	pub content: ext::Braces<ext::Punctuated<DeclStorageLine, Token![;]>>,
 	pub extra_genesis: ext::Opt<AddExtraGenesis>,
 }

substrate/srml/support/procedural/src/storage/transformation.rs

@@ -27,6 +27,7 @@ use proc_macro2::{TokenStream as TokenStream2, Span};
 use syn::{
 	Ident,
 	GenericParam,
+	WhereClause,
 	spanned::Spanned,
 	parse::{
 		Error,
@@ -68,6 +69,7 @@ pub fn decl_storage_impl(input: TokenStream) -> TokenStream {
 		crate_ident: cratename,
 		content: ext::Braces { content: storage_lines, ..},
 		extra_genesis,
+		where_clause,
 		..
 	} = def;
 
@@ -110,6 +112,7 @@ pub fn decl_storage_impl(input: TokenStream) -> TokenStream {
 		&instance_opts,
 		&storage_lines,
 		&extra_genesis.inner,
+		&where_clause,
 	));
 	let decl_storage_items = decl_storage_items(
 		&scrate,
@@ -118,6 +121,7 @@ pub fn decl_storage_impl(input: TokenStream) -> TokenStream {
 		&instance_opts,
 		&cratename,
 		&storage_lines,
+		&where_clause,
 	);
 
 	let decl_store_items = decl_store_items(
@@ -140,6 +144,7 @@ pub fn decl_storage_impl(input: TokenStream) -> TokenStream {
 		&traittype,
 		&instance_opts,
 		&storage_lines,
+		&where_clause,
 	);
 
 	let InstanceOpts {
@@ -156,10 +161,14 @@ pub fn decl_storage_impl(input: TokenStream) -> TokenStream {
 			#decl_store_items
 		}
 		#store_default_struct
-		impl<#traitinstance: #traittype, #instance #bound_instantiable> #storetype for #module_ident<#traitinstance, #instance> {
+		impl<#traitinstance: #traittype, #instance #bound_instantiable> #storetype
+			for #module_ident<#traitinstance, #instance> #where_clause
+		{
 			#impl_store_items
 		}
-		impl<#traitinstance: 'static + #traittype, #instance #bound_instantiable> #module_ident<#traitinstance, #instance> {
+		impl<#traitinstance: 'static + #traittype, #instance #bound_instantiable>
+			#module_ident<#traitinstance, #instance> #where_clause
+		{
 			#impl_store_fns
 			#[doc(hidden)]
 			pub fn store_metadata_functions() -> &'static [#scrate::metadata::StorageEntryMetadata] {
@@ -184,6 +193,7 @@ fn decl_store_extra_genesis(
 	instance_opts: &InstanceOpts,
 	storage_lines: &ext::Punctuated<DeclStorageLine, Token![;]>,
 	extra_genesis: &Option<AddExtraGenesis>,
+	where_clause: &Option<syn::WhereClause>,
 ) -> Result<TokenStream2> {
 
 	let InstanceOpts {
@@ -479,7 +489,26 @@ fn decl_store_extra_genesis(
 
 		let impl_trait = quote!(BuildModuleGenesisStorage<#traitinstance, #inherent_instance>);
 
-		let builders_clone_bound = quote!( #( #builders_clone_bound: Clone ),* );
+		let extend_where_clause = |to_extend: &mut WhereClause| {
+			if let Some(where_clause) = where_clause {
+				to_extend.predicates.extend(where_clause.predicates.iter().cloned());
+			}
+		};
+
+		let mut genesis_where_clause: WhereClause = syn::parse_quote!(
+			where #( #builders_clone_bound: Clone ),*
+		);
+		let mut fn_where_clause = genesis_where_clause.clone();
+
+
+		let mut build_storage_where_clause = genesis_where_clause.clone();
+		extend_where_clause(&mut build_storage_where_clause);
+
+		if is_trait_needed {
+			extend_where_clause(&mut genesis_where_clause);
+		} else if assimilate_require_generic {
+			extend_where_clause(&mut fn_where_clause);
+		}
 
 		let res = quote!{
 			#[derive(#scrate::Serialize, #scrate::Deserialize)]
@@ -487,13 +516,13 @@ fn decl_store_extra_genesis(
 			#[serde(rename_all = "camelCase")]
 			#[serde(deny_unknown_fields)]
 			#serde_bug_bound
-			pub struct GenesisConfig#fparam_struct {
+			pub struct GenesisConfig#fparam_struct #genesis_where_clause {
 				#config_field
 				#genesis_extrafields
 			}
 
 			#[cfg(feature = "std")]
-			impl#fparam_impl Default for GenesisConfig#sparam {
+			impl#fparam_impl Default for GenesisConfig#sparam #genesis_where_clause {
 				fn default() -> Self {
 					GenesisConfig {
 						#config_field_default
@@ -503,14 +532,14 @@ fn decl_store_extra_genesis(
 			}
 
 			#[cfg(feature = "std")]
-			impl#fparam_impl GenesisConfig#sparam where #builders_clone_bound {
+			impl#fparam_impl GenesisConfig#sparam #genesis_where_clause {
 				pub fn build_storage #fn_generic (self) -> std::result::Result<
 					(
 						#scrate::runtime_primitives::StorageOverlay,
 						#scrate::runtime_primitives::ChildrenStorageOverlay,
 					),
 					String
-				> {
+				> #fn_where_clause {
 					let mut storage = Default::default();
 					let mut child_storage = Default::default();
 					self.assimilate_storage::<#fn_traitinstance>(&mut storage, &mut child_storage)?;
@@ -522,7 +551,7 @@ fn decl_store_extra_genesis(
 					self,
 					r: &mut #scrate::runtime_primitives::StorageOverlay,
 					c: &mut #scrate::runtime_primitives::ChildrenStorageOverlay,
-				) -> std::result::Result<(), String> {
+				) -> std::result::Result<(), String> #fn_where_clause {
 					let storage = r;
 
 					#builders
@@ -535,7 +564,7 @@ fn decl_store_extra_genesis(
 
 			#[cfg(feature = "std")]
 			impl#build_storage_impl #scrate::runtime_primitives::#impl_trait
-				for GenesisConfig#sparam where #builders_clone_bound
+				for GenesisConfig#sparam #build_storage_where_clause
 			{
 				fn build_module_genesis_storage(
 					self,
@@ -589,6 +618,7 @@ fn decl_storage_items(
 	instance_opts: &InstanceOpts,
 	cratename: &Ident,
 	storage_lines: &ext::Punctuated<DeclStorageLine, Token![;]>,
+	where_clause: &Option<WhereClause>,
 ) -> TokenStream2 {
 
 	let mut impls = TokenStream2::new();
@@ -728,6 +758,7 @@ fn decl_storage_items(
 			prefix: build_prefix(cratename, name),
 			name,
 			attrs,
+			where_clause,
 		};
 
 		let implementation = match kind {
@@ -899,6 +930,7 @@ fn store_functions_to_metadata (
 	traittype: &syn::TypeParamBound,
 	instance_opts: &InstanceOpts,
 	storage_lines: &ext::Punctuated<DeclStorageLine, Token![;]>,
+	where_clause: &Option<WhereClause>,
 ) -> (TokenStream2, TokenStream2) {
 
 	let InstanceOpts {
@@ -1008,12 +1040,18 @@ fn store_functions_to_metadata (
 
 		let def_get = quote! {
 			#[doc(hidden)]
-			pub struct #struct_name<#traitinstance, #instance #bound_instantiable #equal_default_instance>(pub #scrate::rstd::marker::PhantomData<(#traitinstance #comma_instance)>);
+			pub struct #struct_name<
+				#traitinstance, #instance #bound_instantiable #equal_default_instance
+			>(pub #scrate::rstd::marker::PhantomData<(#traitinstance #comma_instance)>);
+
 			#[cfg(feature = "std")]
 			#[allow(non_upper_case_globals)]
 			static #cache_name: #scrate::once_cell::sync::OnceCell<#scrate::rstd::vec::Vec<u8>> = #scrate::once_cell::sync::OnceCell::INIT;
+
 			#[cfg(feature = "std")]
-			impl<#traitinstance: #traittype, #instance #bound_instantiable> #scrate::metadata::DefaultByte for #struct_name<#traitinstance, #instance> {
+			impl<#traitinstance: #traittype, #instance #bound_instantiable> #scrate::metadata::DefaultByte
+				for #struct_name<#traitinstance, #instance> #where_clause
+			{
 				fn default_byte(&self) -> #scrate::rstd::vec::Vec<u8> {
 					use #scrate::codec::Encode;
 					#cache_name.get_or_init(|| {
@@ -1022,8 +1060,11 @@ fn store_functions_to_metadata (
 					}).clone()
 				}
 			}
+
 			#[cfg(not(feature = "std"))]
-			impl<#traitinstance: #traittype, #instance #bound_instantiable> #scrate::metadata::DefaultByte for #struct_name<#traitinstance, #instance> {
+			impl<#traitinstance: #traittype, #instance #bound_instantiable> #scrate::metadata::DefaultByte
+				for #struct_name<#traitinstance, #instance> #where_clause
+			{
 				fn default_byte(&self) -> #scrate::rstd::vec::Vec<u8> {
 					use #scrate::codec::Encode;
 					let def_val: #value_type = #default;

substrate/srml/support/src/dispatch.rs

@@ -183,6 +183,28 @@ impl<T> Parameter for T where T: Codec + Clone + Eq {}
 /// # fn main() {}
 /// ```
 ///
+/// ## Where clause
+///
+/// Besides the default `origin: T::Origin`, you can also pass other bounds to the module declaration.
+/// This where bound will be replicated to all types generated by this macro. The chaining of multiple
+/// trait bounds with `+` is not supported. If multiple bounds for one type are required, it needs to
+/// be split up into multiple bounds.
+///
+/// ```
+/// # #[macro_use]
+/// # extern crate srml_support;
+/// # use srml_support::dispatch::Result;
+/// # use srml_system::{self as system, ensure_signed};
+/// pub trait Trait: system::Trait where Self::AccountId: From<u32> {}
+///
+/// decl_module! {
+/// 	pub struct Module<T: Trait> for enum Call where origin: T::Origin, T::AccountId: From<u32> {
+/// 		// Your implementation
+/// 	}
+/// }
+/// # fn main() {}
+/// ```
+///
 /// ## Reserved Functions
 ///
 /// The following are reserved function signatures:
@@ -206,15 +228,21 @@ macro_rules! decl_module {
 	// Entry point #1.
 	(
 		$(#[$attr:meta])*
-		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
-		for enum $call_type:ident where origin: $origin_type:ty {
-			$($t:tt)*
+		pub struct $mod_type:ident<
+			$trait_instance:ident: $trait_name:ident
+			$( <I>, I: $instantiable:path $( = $module_default_instance:path )? )?
+		>
+		for enum $call_type:ident where origin: $origin_type:ty $(, $where_ty:ty: $where_bound:path )* {
+			$( $t:tt )*
 		}
 	) => {
 		$crate::decl_module!(@normalize
 			$(#[$attr])*
-			pub struct $mod_type<$trait_instance: $trait_name$(<I>, I: $instantiable $(= $module_default_instance)?)?>
+			pub struct $mod_type<
+				$trait_instance: $trait_name $(<I>, I: $instantiable $(= $module_default_instance)?)?
+			>
 			for enum $call_type where origin: $origin_type, system = system
+			{ $( $where_ty: $where_bound ),* }
 			{}
 			{}
 			{}
@@ -227,15 +255,25 @@ macro_rules! decl_module {
 	// Entry point #2.
 	(
 		$(#[$attr:meta])*
-		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
-		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident {
+		pub struct $mod_type:ident<
+			$trait_instance:ident: $trait_name:ident
+			$( <I>, I: $instantiable:path $( = $module_default_instance:path )? )?
+		>
+		for enum $call_type:ident where
+			origin: $origin_type:ty,
+			system = $system:ident
+			$(, $where_ty:ty: $where_bound:path )*
+		{
 			$($t:tt)*
 		}
 	) => {
 		$crate::decl_module!(@normalize
 			$(#[$attr])*
-			pub struct $mod_type<$trait_instance: $trait_name$(<I>, I: $instantiable $(= $module_default_instance)?)?>
+			pub struct $mod_type<
+				$trait_instance: $trait_name $(<I>, I: $instantiable $( = $module_default_instance )? )?
+			>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $where_ty: $where_bound ),* }
 			{}
 			{}
 			{}
@@ -251,6 +289,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{}
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -265,6 +304,7 @@ macro_rules! decl_module {
 			$(#[$attr])*
 			pub struct $mod_type<$trait_instance: $trait_name$(<I>, I: $instantiable $(= $module_default_instance)?)?>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $vis fn deposit_event $(<$dpeg $(, $dpeg_instance)?>)* () = default; }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -278,6 +318,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{}
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -294,6 +335,7 @@ macro_rules! decl_module {
 			$(#[$attr])*
 			pub struct $mod_type<$trait_instance: $trait_name$(<I>, I: $instantiable $(= $module_default_instance)?)?>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $vis fn deposit_event $(<$dpeg $(, $dpeg_instance)?>)* ($( $param_name: $param ),* ) { $( $impl )* } }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -307,6 +349,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{}
@@ -321,6 +364,7 @@ macro_rules! decl_module {
 			$(#[$attr])*
 			pub struct $mod_type<$trait_instance: $trait_name$(<I>, I: $instantiable $(= $module_default_instance)?)?>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ $( $on_initialize )* }
 			{ fn on_finalize( $( $param_name : $param ),* ) { $( $impl )* } }
@@ -334,6 +378,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{}
@@ -352,6 +397,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{}
 		{ $( $on_finalize:tt )* }
@@ -366,6 +412,7 @@ macro_rules! decl_module {
 			$(#[$attr])*
 			pub struct $mod_type<$trait_instance: $trait_name$(<I>, I: $instantiable $(= $module_default_instance)?)?>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ fn on_initialize( $( $param_name : $param ),* ) { $( $impl )* } }
 			{ $( $on_finalize )* }
@@ -379,6 +426,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{}
 		{ $( $on_finalize:tt )* }
@@ -400,6 +448,7 @@ macro_rules! decl_module {
 			$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?
 		>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -416,6 +465,7 @@ macro_rules! decl_module {
 				$trait_instance: $trait_name$(<I>, I: $instantiable $(= $module_default_instance)?)?
 			>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -434,6 +484,7 @@ macro_rules! decl_module {
 			$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?
 		>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -451,6 +502,7 @@ macro_rules! decl_module {
 				$( <I>, $instance: $instantiable $(= $module_default_instance)? )?
 			>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -473,6 +525,7 @@ macro_rules! decl_module {
 			$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?
 			>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -492,6 +545,7 @@ macro_rules! decl_module {
 				$trait_instance: $trait_name$(<I>, $instance: $instantiable $(= $module_default_instance)?)?
 			>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -517,6 +571,7 @@ macro_rules! decl_module {
 				$trait_name:ident$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?
 			>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -535,6 +590,7 @@ macro_rules! decl_module {
 				$trait_instance: $trait_name$(<I>, $instance: $instantiable $(= $module_default_instance)?)?
 			>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -554,6 +610,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -578,6 +635,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -602,6 +660,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -619,6 +678,7 @@ macro_rules! decl_module {
 			$(#[$attr])*
 			pub struct $mod_type<$trait_instance: $trait_name$(<I>, $instance: $instantiable $(= $module_default_instance)?)?>
 			for enum $call_type where origin: $origin_type, system = $system
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -640,6 +700,7 @@ macro_rules! decl_module {
 		$(#[$attr:meta])*
 		pub struct $mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path $(= $module_default_instance:path)?)?>
 		for enum $call_type:ident where origin: $origin_type:ty, system = $system:ident
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -653,6 +714,7 @@ macro_rules! decl_module {
 			for enum $call_type where origin: $origin_type, system = $system {
 				$( $dispatchables )*
 			}
+			{ $( $other_where_bounds )* }
 			{ $( $deposit_event )* }
 			{ $( $on_initialize )* }
 			{ $( $on_finalize )* }
@@ -684,14 +746,18 @@ macro_rules! decl_module {
 	(@impl_deposit_event
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, I: $instantiable:path)?>;
 		$system:ident;
+		{ $( $other_where_bounds:tt )* }
 	) => {};
 
 	(@impl_deposit_event
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
 		$system:ident;
+		{ $( $other_where_bounds:tt )* }
 		$vis:vis fn deposit_event$(<$event_trait_instance:ident $(, $event_instance:ident)?>)?() = default;
 	) => {
-		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?> $module<$trait_instance $(, $instance)?> {
+		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?> $module<$trait_instance $(, $instance)?>
+			where $( $other_where_bounds )*
+		{
 			$vis fn deposit_event(event: Event$(<$event_trait_instance $(, $event_instance)?>)?) {
 				<$system::Module<$trait_instance>>::deposit_event(
 					<$trait_instance as $trait_name$(<$instance>)?>::Event::from(event).into()
@@ -703,9 +769,12 @@ macro_rules! decl_module {
 	(@impl_deposit_event
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
 		$system:ident;
+		{ $( $other_where_bounds:tt )* }
 		$vis:vis fn deposit_event($param:ident : $param_ty:ty) { $( $impl:tt )* }
 	) => {
-		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?> $module<$trait_instance $(, $instance)?> {
+		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?> $module<$trait_instance $(, $instance)?>
+			where $( $other_where_bounds )*
+		{
 			$vis fn deposit_event($param: $param_ty) {
 				$( $impl )*
 			}
@@ -714,11 +783,12 @@ macro_rules! decl_module {
 
 	(@impl_on_initialize
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 		fn on_initialize() { $( $impl:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OnInitialize<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn on_initialize(_block_number_not_used: $trait_instance::BlockNumber) { $( $impl )* }
 		}
@@ -726,11 +796,12 @@ macro_rules! decl_module {
 
 	(@impl_on_initialize
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 		fn on_initialize($param:ident : $param_ty:ty) { $( $impl:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OnInitialize<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn on_initialize($param: $param_ty) { $( $impl )* }
 		}
@@ -738,20 +809,22 @@ macro_rules! decl_module {
 
 	(@impl_on_initialize
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OnInitialize<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{}
 	};
 
 	(@impl_on_finalize
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 		fn on_finalize() { $( $impl:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OnFinalize<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn on_finalize(_block_number_not_used: $trait_instance::BlockNumber) { $( $impl )* }
 		}
@@ -759,11 +832,12 @@ macro_rules! decl_module {
 
 	(@impl_on_finalize
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 		fn on_finalize($param:ident : $param_ty:ty) { $( $impl:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OnFinalize<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn on_finalize($param: $param_ty) { $( $impl )* }
 		}
@@ -771,21 +845,23 @@ macro_rules! decl_module {
 
 	(@impl_on_finalize
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OnFinalize<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{
 		}
 	};
 
 	(@impl_offchain
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 		fn offchain_worker() { $( $impl:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OffchainWorker<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn generate_extrinsics(_block_number_not_used: $trait_instance::BlockNumber) { $( $impl )* }
 		}
@@ -793,11 +869,12 @@ macro_rules! decl_module {
 
 	(@impl_offchain
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 		fn offchain_worker($param:ident : $param_ty:ty) { $( $impl:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OffchainWorker<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn generate_extrinsics($param: $param_ty) { $( $impl )* }
 		}
@@ -805,10 +882,11 @@ macro_rules! decl_module {
 
 	(@impl_offchain
 		$module:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>;
+		{ $( $other_where_bounds:tt )* }
 	) => {
 		impl<$trait_instance: $trait_name$(<I>, $instance: $instantiable)?>
 			$crate::runtime_primitives::traits::OffchainWorker<$trait_instance::BlockNumber>
-			for $module<$trait_instance$(, $instance)?>
+			for $module<$trait_instance$(, $instance)?> where $( $other_where_bounds )*
 		{}
 	};
 
@@ -884,6 +962,7 @@ macro_rules! decl_module {
 		$( #[$attr:meta] )*
 		$call_type:ident;
 		<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?>
+		{ $( $other_where_bounds:tt )* }
 		{ $( $generated_variants:tt )* }
 		{ $( $current_params:tt )* }
 		variant $fn_name:ident;
@@ -897,6 +976,7 @@ macro_rules! decl_module {
 			$( #[$attr] )*
 			$call_type;
 			<$trait_instance: $trait_name $(<I>, $instance: $instantiable $(= $module_default_instance)? )?>
+			{ $( $other_where_bounds )* }
 			{ $( $generated_variants )* }
 			{
 				$( $current_params )*
@@ -914,6 +994,7 @@ macro_rules! decl_module {
 		$( #[$attr:meta] )*
 		$call_type:ident;
 		<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?>
+		{ $( $other_where_bounds:tt )* }
 		{ $( $generated_variants:tt )* }
 		{ $( $current_params:tt )* }
 		variant $fn_name:ident;
@@ -926,6 +1007,7 @@ macro_rules! decl_module {
 			$( #[$attr] )*
 			$call_type;
 			<$trait_instance: $trait_name $(<I>, $instance: $instantiable $(= $module_default_instance)? )?>
+			{ $( $other_where_bounds )* }
 			{ $( $generated_variants )* }
 			{
 				$( $current_params )*
@@ -941,6 +1023,7 @@ macro_rules! decl_module {
 		$( #[$attr:meta] )*
 		$call_type:ident;
 		<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?>
+		{ $( $other_where_bounds:tt )* }
 		{ $( $generated_variants:tt )* }
 		{ $( $current_params:tt )* }
 		variant $fn_name:ident;
@@ -955,6 +1038,7 @@ macro_rules! decl_module {
 			$( #[$attr] )*
 			$call_type;
 			<$trait_instance: $trait_name $(<I>, $instance: $instantiable $(= $module_default_instance)? )?>
+			{ $( $other_where_bounds )* }
 			{
 				$( $generated_variants )*
 				#[allow(non_camel_case_types)]
@@ -975,12 +1059,15 @@ macro_rules! decl_module {
 		$( #[$attr:meta] )*
 		$call_type:ident;
 		<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path $(= $module_default_instance:path)?)?>
+		{ $( $other_where_bounds:tt )* }
 		{ $( $generated_variants:tt )* }
 		{}
 	) => {
 		#[derive($crate::codec::Encode, $crate::codec::Decode)]
 		$( #[$attr] )*
-		pub enum $call_type<$trait_instance: $trait_name$(<I>, $instance: $instantiable $( = $module_default_instance)?)?> {
+		pub enum $call_type<$trait_instance: $trait_name$(<I>, $instance: $instantiable $( = $module_default_instance)?)?>
+			where $( $other_where_bounds )*
+		{
 			#[doc(hidden)]
 			#[codec(skip)]
 			__PhantomItem($crate::rstd::marker::PhantomData<($trait_instance $(, $instance)?)>, $crate::dispatch::Never),
@@ -1006,6 +1093,7 @@ macro_rules! decl_module {
 				{ $($fn_instance:ident: $fn_instantiable:path)? }
 			)*
 		}
+		{ $( $other_where_bounds:tt )* }
 		{ $( $deposit_event:tt )* }
 		{ $( $on_initialize:tt )* }
 		{ $( $on_finalize:tt )* }
@@ -1020,36 +1108,43 @@ macro_rules! decl_module {
 		pub struct $mod_type<
 			$trait_instance: $trait_name
 			$(<I>, $instance: $instantiable $( = $module_default_instance)?)?
-		>($crate::rstd::marker::PhantomData<($trait_instance $(, $instance)?)>);
+		>($crate::rstd::marker::PhantomData<($trait_instance $(, $instance)?)>) where
+			$( $other_where_bounds )*;
 
 		$crate::decl_module! {
 			@impl_on_initialize
 			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>;
+			{ $( $other_where_bounds )* }
 			$( $on_initialize )*
 		}
 
 		$crate::decl_module! {
 			@impl_on_finalize
 			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>;
+			{ $( $other_where_bounds )* }
 			$( $on_finalize )*
 		}
 
 		$crate::decl_module! {
 			@impl_offchain
 			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>;
+			{ $( $other_where_bounds )* }
 			$( $offchain )*
 		}
 		$crate::decl_module! {
 			@impl_deposit_event
 			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>;
 			$system;
+			{ $( $other_where_bounds )* }
 			$( $deposit_event )*
 		}
 
 		/// Can also be called using [`Call`].
 		///
 		/// [`Call`]: enum.Call.html
-		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $mod_type<$trait_instance $(, $instance)?> {
+		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $mod_type<$trait_instance $(, $instance)?>
+			where $( $other_where_bounds )*
+		{
 			$(
 				$crate::decl_module! {
 					@impl_function
@@ -1069,6 +1164,7 @@ macro_rules! decl_module {
 			$( #[$attr] )*
 			$call_type;
 			<$trait_instance: $trait_name $(<I>, $instance: $instantiable $(= $module_default_instance)? )?>
+			{ $( $other_where_bounds )* }
 			{}
 			{}
 			$(
@@ -1083,7 +1179,7 @@ macro_rules! decl_module {
 
 		// Implement weight calculation function for Call
 		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::Weighable
-			for $call_type<$trait_instance $(, $instance)?>
+			for $call_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn weight(&self, _len: usize) -> $crate::dispatch::Weight {
 				match self {
@@ -1096,7 +1192,7 @@ macro_rules! decl_module {
 		// manual implementation of clone/eq/partialeq because using derive erroneously requires
 		// clone/eq/partialeq from T.
 		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::Clone
-			for $call_type<$trait_instance $(, $instance)?>
+			for $call_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn clone(&self) -> Self {
 				match *self {
@@ -1109,7 +1205,7 @@ macro_rules! decl_module {
 			}
 		}
 		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::PartialEq
-			for $call_type<$trait_instance $(, $instance)?>
+			for $call_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn eq(&self, _other: &Self) -> bool {
 				match *self {
@@ -1131,12 +1227,12 @@ macro_rules! decl_module {
 			}
 		}
 		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::Eq
-			for $call_type<$trait_instance $(, $instance)?>
+			for $call_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{}
 
 		#[cfg(feature = "std")]
 		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::fmt::Debug
-			for $call_type<$trait_instance $(, $instance)?>
+			for $call_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{
 			fn fmt(
 				&self,
@@ -1156,7 +1252,7 @@ macro_rules! decl_module {
 		}
 
 		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::Dispatchable
-			for $call_type<$trait_instance $(, $instance)?>
+			for $call_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{
 			type Trait = $trait_instance;
 			type Origin = $origin_type;
@@ -1176,12 +1272,14 @@ macro_rules! decl_module {
 			}
 		}
 		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $crate::dispatch::Callable<$trait_instance>
-			for $mod_type<$trait_instance $(, $instance)?>
+			for $mod_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{
 			type Call = $call_type<$trait_instance $(, $instance)?>;
 		}
 
-		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $mod_type<$trait_instance $(, $instance)?> {
+		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $mod_type<$trait_instance $(, $instance)?>
+			where $( $other_where_bounds )*
+		{
 			#[doc(hidden)]
 			pub fn dispatch<D: $crate::dispatch::Dispatchable<Trait = $trait_instance>>(
 				d: D,
@@ -1191,11 +1289,19 @@ macro_rules! decl_module {
 			}
 		}
 		$crate::__dispatch_impl_metadata! {
-			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $call_type $origin_type
-			{$( $(#[doc = $doc_attr])* fn $fn_name($from $(, $(#[$codec_attr])* $param_name : $param )*); )*}
+			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>
+			{ $( $other_where_bounds )* }
+			$call_type $origin_type
+			{
+				$(
+					$(#[doc = $doc_attr])*
+					fn $fn_name($from $(, $(#[$codec_attr])* $param_name : $param )*);
+				)*
+			}
 		}
 		$crate::__impl_module_constants_metadata ! {
 			$mod_type<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?>
+			{ $( $other_where_bounds )* }
 			$( $constants )*
 		}
 	}
@@ -1265,9 +1371,12 @@ macro_rules! impl_outer_dispatch {
 macro_rules! __dispatch_impl_metadata {
 	(
 		$mod_type:ident<$trait_instance:ident: $trait_name:ident$(<I>, $instance:ident: $instantiable:path)?>
+		{ $( $other_where_bounds:tt )* }
 		$($rest:tt)*
 	) => {
-		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $mod_type<$trait_instance $(, $instance)?> {
+		impl<$trait_instance: $trait_name $(<I>, $instance: $instantiable)?> $mod_type<$trait_instance $(, $instance)?>
+			where $( $other_where_bounds )*
+		{
 			#[doc(hidden)]
 			pub fn call_functions() -> &'static [$crate::dispatch::FunctionMetadata] {
 				$crate::__call_to_functions!($($rest)*)
@@ -1283,6 +1392,7 @@ macro_rules! __impl_module_constants_metadata {
 	// Without instance
 	(
 		$mod_type:ident<$trait_instance:ident: $trait_name:ident>
+		{ $( $other_where_bounds:tt )* }
 		$(
 			$( #[doc = $doc_attr:tt] )*
 			$name:ident: $type:ty = $value:expr;
@@ -1292,6 +1402,7 @@ macro_rules! __impl_module_constants_metadata {
 			$crate::__impl_module_constants_metadata! {
 				GENERATE_CODE
 				$mod_type<$trait_instance: $trait_name>
+				{ $( $other_where_bounds )* }
 				$(
 					$( #[doc = $doc_attr] )*
 					[< $name DefaultByteGetter >]
@@ -1303,6 +1414,7 @@ macro_rules! __impl_module_constants_metadata {
 	// With instance
 	(
 		$mod_type:ident<$trait_instance:ident: $trait_name:ident<I>, $instance:ident: $instantiable:path>
+		{ $( $other_where_bounds:tt )* }
 		$(
 			$( #[doc = $doc_attr:tt] )*
 			$name:ident: $type:ty = $value:expr;
@@ -1312,6 +1424,7 @@ macro_rules! __impl_module_constants_metadata {
 			$crate::__impl_module_constants_metadata! {
 				GENERATE_CODE
 				$mod_type<$trait_instance: $trait_name<I>, $instance: $instantiable>
+				{ $( $other_where_bounds )* }
 				$(
 					$( #[doc = $doc_attr] )*
 					[< $name DefaultByteGetter >]
@@ -1323,6 +1436,7 @@ macro_rules! __impl_module_constants_metadata {
 	// Do the code generation
 	(GENERATE_CODE
 		$mod_type:ident<$trait_instance:ident: $trait_name:ident $(<I>, $instance:ident: $instantiable:path)?>
+		{ $( $other_where_bounds:tt )* }
 		$(
 			$( #[doc = $doc_attr:tt] )*
 			$default_byte_name:ident
@@ -1334,7 +1448,7 @@ macro_rules! __impl_module_constants_metadata {
 		)*
 	) => {
 		impl<$trait_instance: 'static + $trait_name $(<I>, $instance: $instantiable)?>
-			$mod_type<$trait_instance $(, $instance)?>
+			$mod_type<$trait_instance $(, $instance)?> where $( $other_where_bounds )*
 		{
 			#[doc(hidden)]
 			pub fn module_constants_metadata() -> &'static [$crate::dispatch::ModuleConstantMetadata] {
@@ -1391,14 +1505,16 @@ macro_rules! __impl_module_constants_metadata {
 macro_rules! __call_to_functions {
 	(
 		$call_type:ident $origin_type:ty
-			{$(
+		{
+			$(
 				$(#[doc = $doc_attr:tt])*
 				fn $fn_name:ident($from:ident
 					$(
 						, $(#[$codec_attr:ident])* $param_name:ident : $param:ty
 					)*
 				);
-			)*}
+			)*
+		}
 	) => {
 		$crate::__functions_to_metadata!(0; $origin_type;; $(
 			fn $fn_name( $($(#[$codec_attr])* $param_name: $param ),* );
@@ -1523,7 +1639,7 @@ mod tests {
 	use super::*;
 	use crate::runtime_primitives::traits::{OnInitialize, OnFinalize};
 
-	pub trait Trait: Sized {
+	pub trait Trait: system::Trait + Sized where Self::AccountId: From<u32> {
 		type Origin;
 		type BlockNumber: Into<u32>;
 		type Call: From<Call<Self>>;
@@ -1532,13 +1648,17 @@ mod tests {
 	pub mod system {
 		use super::Result;
 
+		pub trait Trait {
+			type AccountId;
+		}
+
 		pub fn ensure_root<R>(_: R) -> Result {
 			Ok(())
 		}
 	}
 
 	decl_module! {
-		pub struct Module<T: Trait> for enum Call where origin: T::Origin {
+		pub struct Module<T: Trait> for enum Call where origin: T::Origin, T::AccountId: From<u32> {
 			/// Hi, this is a comment.
 			fn aux_0(_origin) -> Result { unreachable!() }
 			fn aux_1(_origin, #[compact] _data: u32) -> Result { unreachable!() }
@@ -1641,6 +1761,10 @@ mod tests {
 		}
 	}
 
+	impl system::Trait for TraitImpl {
+		type AccountId = u32;
+	}
+
 	#[test]
 	fn module_json_metadata() {
 		let metadata = Module::<TraitImpl>::call_functions();

substrate/srml/support/test/tests/instance.rs

@@ -37,14 +37,18 @@ pub trait Currency {}
 mod module1 {
 	use super::*;
 
-	pub trait Trait<I>: system::Trait {
+	pub trait Trait<I>: system::Trait where <Self as system::Trait>::BlockNumber: From<u32> {
 		type Event: From<Event<Self, I>> + Into<<Self as system::Trait>::Event>;
 		type Origin: From<Origin<Self, I>>;
 		type SomeParameter: Get<u32>;
+		type GenericType: Default + Clone + parity_codec::Codec;
 	}
 
 	srml_support::decl_module! {
-		pub struct Module<T: Trait<I>, I: InstantiableThing> for enum Call where origin: <T as system::Trait>::Origin {
+		pub struct Module<T: Trait<I>, I: InstantiableThing> for enum Call where
+			origin: <T as system::Trait>::Origin,
+			T::BlockNumber: From<u32>
+		{
 			fn offchain_worker() {}
 
 			fn deposit_event<T, I>() = default;
@@ -56,11 +60,20 @@ mod module1 {
 	}
 
 	srml_support::decl_storage! {
-		trait Store for Module<T: Trait<I>, I: InstantiableThing> as Module1 {
-			pub Value config(value): u64;
+		trait Store for Module<T: Trait<I>, I: InstantiableThing> as Module1 where
+			T::BlockNumber: From<u32> + std::fmt::Display
+		{
+			pub Value config(value): T::GenericType;
 			pub Map: map u32 => u64;
 			pub LinkedMap: linked_map u32 => u64;
 		}
+
+		add_extra_genesis {
+			config(test) : T::BlockNumber;
+			build(|_, _, config: &Self| {
+				println!("{}", config.test);
+			});
+		}
 	}
 
 	srml_support::decl_event! {
@@ -72,14 +85,16 @@ mod module1 {
 
 	#[derive(PartialEq, Eq, Clone)]
 	#[cfg_attr(feature = "std", derive(Debug))]
-	pub enum Origin<T: Trait<I>, I> {
+	pub enum Origin<T: Trait<I>, I> where T::BlockNumber: From<u32> {
 		Members(u32),
 		_Phantom(std::marker::PhantomData<(T, I)>),
 	}
 
 	pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"12345678";
 
-	impl<T: Trait<I>, I: InstantiableThing> ProvideInherent for Module<T, I> {
+	impl<T: Trait<I>, I: InstantiableThing> ProvideInherent for Module<T, I> where
+		T::BlockNumber: From<u32>
+	{
 		type Call = Call<T, I>;
 		type Error = MakeFatalError<RuntimeString>;
 		const INHERENT_IDENTIFIER: InherentIdentifier = INHERENT_IDENTIFIER;
@@ -88,7 +103,7 @@ mod module1 {
 			unimplemented!();
 		}
 
-		fn check_inherent(_call: &Self::Call, _data: &InherentData) -> std::result::Result<(), Self::Error> {
+		fn check_inherent(_: &Self::Call, _: &InherentData) -> std::result::Result<(), Self::Error> {
 			unimplemented!();
 		}
 	}
@@ -109,7 +124,9 @@ mod module2 {
 	impl<T: Trait<I>, I: Instance> Currency for Module<T, I> {}
 
 	srml_support::decl_module! {
-		pub struct Module<T: Trait<I>, I: Instance=DefaultInstance> for enum Call where origin: <T as system::Trait>::Origin {
+		pub struct Module<T: Trait<I>, I: Instance=DefaultInstance> for enum Call where
+			origin: <T as system::Trait>::Origin
+		{
 			fn deposit_event<T, I>() = default;
 		}
 	}
@@ -176,11 +193,13 @@ impl module1::Trait<module1::Instance1> for Runtime {
 	type Event = Event;
 	type Origin = Origin;
 	type SomeParameter = SomeValue;
+	type GenericType = u32;
 }
 impl module1::Trait<module1::Instance2> for Runtime {
 	type Event = Event;
 	type Origin = Origin;
 	type SomeParameter = SomeValue;
+	type GenericType = u32;
 }
 impl module2::Trait for Runtime {
 	type Amount = u16;
@@ -228,10 +247,10 @@ srml_support::construct_runtime!(
 	{
 		System: system::{Module, Call, Event},
 		Module1_1: module1::<Instance1>::{
-			Module, Call, Storage, Event<T>, Config, Origin<T>, Inherent
+			Module, Call, Storage, Event<T>, Config<T>, Origin<T>, Inherent
 		},
 		Module1_2: module1::<Instance2>::{
-			Module, Call, Storage, Event<T>, Config, Origin<T>, Inherent
+			Module, Call, Storage, Event<T>, Config<T>, Origin<T>, Inherent
 		},
 		Module2: module2::{Module, Call, Storage, Event<T>, Config<T>, Origin<T>, Inherent},
 		Module2_1: module2::<Instance1>::{
@@ -255,9 +274,11 @@ fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher> {
 	GenesisConfig{
 		module1_Instance1: Some(module1::GenesisConfig {
 			value: 3,
+			test: 2,
 		}),
 		module1_Instance2: Some(module1::GenesisConfig {
 			value: 4,
+			test: 5,
 		}),
 		module2: Some(module2::GenesisConfig {
 			value: 4,