Translation for linked map

srml/support/procedural/src/storage/instance_trait.rs

@@ -28,6 +28,7 @@ pub(crate) const DEFAULT_INSTANTIABLE_TRAIT_NAME: &str = "__GeneratedInstantiabl
 // prefix for consts in trait Instance
 pub(crate) const PREFIX_FOR: &str = "PREFIX_FOR_";
 pub(crate) const HEAD_KEY_FOR: &str = "HEAD_KEY_FOR_";
+pub(crate) const LINKED_MAP_KEY_FORMAT_FOR: &str = "LINKED_MAP_KEY_FORMAT_FOR_";
 
 // Used to generate the const:
 // `const $name: &'static str = $value_prefix ++ instance_prefix ++ $value_suffix`

srml/support/procedural/src/storage/storage_struct.rs

@@ -20,7 +20,7 @@ use proc_macro2::TokenStream;
 use quote::quote;
 use super::{
 	DeclStorageDefExt, StorageLineTypeDef,
-	instance_trait::{PREFIX_FOR, HEAD_KEY_FOR},
+	instance_trait::{PREFIX_FOR, HEAD_KEY_FOR, LINKED_MAP_KEY_FORMAT_FOR},
 };
 
 fn from_optional_value_to_query(is_option: bool, default: &Option<syn::Expr>) -> TokenStream {
@@ -156,21 +156,51 @@ pub fn decl_and_impl(scrate: &TokenStream, def: &DeclStorageDefExt) -> TokenStre
 					quote!( #prefix.as_bytes() )
 				};
 
+				let (key_format_type, key_format_decl) = {
+					let name = syn::Ident::new(
+						&format!("{}{}", LINKED_MAP_KEY_FORMAT_FOR, line.name),
+						proc_macro2::Span::call_site(),
+					);
+
+					let format_type = quote!( #name<#optional_instance>);
+
+					let optional_phantom = optional_instance
+						.as_ref()
+						.map(|instance| quote!( #scrate::rstd::marker::PhantomData<#instance> ));
+
+					let struct_decl = quote!(
+						#visibility struct #format_type(#optional_phantom);
+					);
+
+					let format_impl = quote!(
+						impl<#optional_instance_bound> #scrate::storage::generator::LinkedMapKeyFormat
+							for #format_type
+						{
+							type Hasher = #scrate::#hasher;
+
+							fn head_key() -> &'static [u8] {
+								#head_key
+							}
+						}
+					);
+
+					(format_type, quote!( #struct_decl #format_impl ))
+				};
+
 				quote!(
+					#key_format_decl
+
 					impl<#impl_trait> #scrate::#storage_generator_trait for #storage_struct
 					#optional_storage_where_clause
 					{
 						type Query = #query_type;
 						type Hasher = #scrate::#hasher;
+						type KeyFormat = #key_format_type;
 
 						fn prefix() -> &'static [u8] {
 							#final_prefix
 						}
 
-						fn head_key() -> &'static [u8] {
-							#head_key
-						}
-
 						fn from_optional_value_to_query(v: Option<#value_type>) -> Self::Query {
 							#from_optional_value_to_query
 						}