use custom ext::Opt for default_value in DeclStorageLine (#1722)

instead of ext::Seq

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

@@ -74,8 +74,7 @@ struct AddExtraGenesisLine {
 	pub extra_field: ext::Parens<Ident>,
 	pub coldot_token: Token![:],
 	pub extra_type: syn::Type,
-	// FIXME #1570: use a custom ext::Option instead (syn option on '=' fails)
-	pub default_value: ext::Seq<DeclStorageDefault>,
+	pub default_value: ext::Opt<DeclStorageDefault>,
 }
 
 #[derive(Parse, ToTokens, Debug)]
@@ -91,8 +90,7 @@ struct DeclStorageLine {
 	pub build: Option<DeclStorageBuild>,
 	pub coldot_token: Token![:],
 	pub storage_type: DeclStorageType,
-	// FIXME #1570: use a custom ext::Option instead (syn option on '=' fails)
-	pub default_value: ext::Seq<DeclStorageDefault>,
+	pub default_value: ext::Opt<DeclStorageDefault>,
 }
 
 

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

@@ -203,7 +203,7 @@ fn decl_store_extra_genesis(
 			config_field.extend(quote!( pub #ident: #storage_type, ));
 			opt_build = Some(build.as_ref().map(|b| &b.expr.content).map(|b|quote!( #b ))
 				.unwrap_or_else(|| quote!( (|config: &GenesisConfig<#traitinstance>| config.#ident.clone()) )));
-			let fielddefault = default_value.inner.get(0).as_ref().map(|d| &d.expr).map(|d|
+			let fielddefault = default_value.inner.as_ref().map(|d| &d.expr).map(|d|
 				if type_infos.is_option {
 					quote!( #d.unwrap_or_default() )
 				} else {
@@ -270,7 +270,7 @@ fn decl_store_extra_genesis(
 					genesis_extrafields.extend(quote!{
 						#attrs pub #extrafield: #extra_type,
 					});
-					let extra_default = default_value.inner.get(0).map(|d| &d.expr).map(|e| quote!{ #e })
+					let extra_default = default_value.inner.as_ref().map(|d| &d.expr).map(|e| quote!{ #e })
 						.unwrap_or_else(|| quote!( Default::default() ));
 					genesis_extrafields_default.extend(quote!{
 						#extrafield: #extra_default,
@@ -403,7 +403,7 @@ fn decl_storage_items(
 
 		let type_infos = get_type_infos(storage_type);
 		let gettype = type_infos.full_type;
-		let fielddefault = default_value.inner.get(0).as_ref().map(|d| &d.expr).map(|d| quote!( #d ))
+		let fielddefault = default_value.inner.as_ref().map(|d| &d.expr).map(|d| quote!( #d ))
 			.unwrap_or_else(|| quote!{ Default::default() });
 
 		let typ = type_infos.typ;
@@ -643,7 +643,7 @@ fn store_functions_to_metadata (
 				#scrate::storage::generator::StorageFunctionModifier::Default
 			}
 		};
-		let default = default_value.inner.get(0).as_ref().map(|d| &d.expr)
+		let default = default_value.inner.as_ref().map(|d| &d.expr)
 			.map(|d| {
 				quote!( #d )
 			})

substrate/srml/support/procedural/tools/src/syn_ext.rs

@@ -191,33 +191,25 @@ impl ToTokens for OuterAttributes {
 }
 
 #[derive(Debug)]
-pub struct Seq<P> {
-	pub inner: Vec<P>,
+pub struct Opt<P> {
+	pub inner: Option<P>,
 }
 
-impl<P: Parse> Parse for Seq<P> {
+impl<P: Parse> Parse for Opt<P> {
 	// Note that it cost a double parsing (same as enum derive)
 	fn parse(input: ParseStream) -> Result<Self> {
-		let mut inner = Vec::new();
-		loop {
-			let fork = input.fork();
-			let res: Result<P> = fork.parse();
-			match res {
-				Ok(_item) => {
-					// move cursor
-					let item: P = input.parse().expect("Same parsing ran before");
-					inner.push(item);
-				},
-				Err(_e) => break,
-			}
-		}
-		Ok(Seq { inner })
+		let inner = match input.fork().parse::<P>() {
+			Ok(_item) => Some(input.parse().expect("Same parsing ran before")),
+			Err(_e) => None,
+		};
+
+		Ok(Opt { inner })
 	}
 }
 
-impl<P: ToTokens> ToTokens for Seq<P> {
+impl<P: ToTokens> ToTokens for Opt<P> {
 	fn to_tokens(&self, tokens: &mut T2) {
-		for p in self.inner.iter() {
+		if let Some(ref p) = self.inner {
 			p.to_tokens(tokens);
 		}
 	}