handle doc on type_value (#10132)

substrate/frame/support/procedural/src/pallet/expand/type_value.rs

@@ -59,7 +59,10 @@ pub fn expand_type_values(def: &mut Def) -> proc_macro2::TokenStream {
 			(Default::default(), Default::default())
 		};
 
+		let docs = &type_value.docs;
+
 		expand.extend(quote::quote_spanned!(type_value.attr_span =>
+			#( #[doc = #docs] )*
 			#vis struct #ident<#struct_use_gen>(core::marker::PhantomData<((), #struct_use_gen)>);
 			impl<#struct_impl_gen> #frame_support::traits::Get<#type_> for #ident<#struct_use_gen>
 			#where_clause

substrate/frame/support/procedural/src/pallet/parse/type_value.rs

@@ -38,6 +38,8 @@ pub struct TypeValueDef {
 	pub where_clause: Option<syn::WhereClause>,
 	/// The span of the pallet::type_value attribute.
 	pub attr_span: proc_macro2::Span,
+	/// Docs on the item.
+	pub docs: Vec<syn::Lit>,
 }
 
 impl TypeValueDef {
@@ -53,9 +55,18 @@ impl TypeValueDef {
 			return Err(syn::Error::new(item.span(), msg))
 		};
 
-		if !item.attrs.is_empty() {
-			let msg = "Invalid pallet::type_value, unexpected attribute";
-			return Err(syn::Error::new(item.attrs[0].span(), msg))
+		let mut docs = vec![];
+		for attr in &item.attrs {
+			if let Ok(syn::Meta::NameValue(meta)) = attr.parse_meta() {
+				if meta.path.get_ident().map_or(false, |ident| ident == "doc") {
+					docs.push(meta.lit);
+					continue
+				}
+			}
+
+			let msg = "Invalid pallet::type_value, unexpected attribute, only doc attribute are \
+				allowed";
+			return Err(syn::Error::new(attr.span(), msg))
 		}
 
 		if let Some(span) = item
@@ -106,6 +117,7 @@ impl TypeValueDef {
 			type_,
 			instances,
 			where_clause,
+			docs,
 		})
 	}
 }