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;