Support pallet::storage conditional compilation (#8324)

* Support pallet::storage conditional compilation.

* Add docs for cfg attributes.

* Keep strong types for get cfg attrs return.

* Update frame/support/procedural/src/pallet/parse/helper.rs

* Update frame/support/procedural/src/pallet/parse/storage.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

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

@@ -172,7 +172,7 @@ impl CallDef {
 				}
 
 				let mut call_var_attrs: Vec<FunctionAttr> =
-					helper::take_item_attrs(&mut method.attrs)?;
+					helper::take_item_pallet_attrs(&mut method.attrs)?;
 
 				if call_var_attrs.len() != 1 {
 					let msg = if call_var_attrs.is_empty() {
@@ -193,7 +193,7 @@ impl CallDef {
 					};
 
 					let arg_attrs: Vec<ArgAttrIsCompact> =
-						helper::take_item_attrs(&mut arg.attrs)?;
+						helper::take_item_pallet_attrs(&mut arg.attrs)?;
 
 					if arg_attrs.len() > 1 {
 						let msg = "Invalid pallet::call, argument has too many attributes";

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

@@ -309,7 +309,7 @@ impl ConfigDef {
 				|| check_event_type(frame_system, trait_item, has_instance)?;
 
 			// Parse for constant
-			let type_attrs_const: Vec<TypeAttrConst> = helper::take_item_attrs(trait_item)?;
+			let type_attrs_const: Vec<TypeAttrConst> = helper::take_item_pallet_attrs(trait_item)?;
 
 			if type_attrs_const.len() > 1 {
 				let msg = "Invalid attribute in pallet::config, only one attribute is expected";
@@ -339,7 +339,7 @@ impl ConfigDef {
 			}
 		}
 
-		let attr: Option<DisableFrameSystemSupertraitCheck> = helper::take_first_item_attr(
+		let attr: Option<DisableFrameSystemSupertraitCheck> = helper::take_first_item_pallet_attr(
 			&mut item.attrs
 		)?;
 

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

@@ -163,7 +163,7 @@ impl EventDef {
 			return Err(syn::Error::new(item.span(), "Invalid pallet::event, expected item enum"))
 		};
 
-		let event_attrs: Vec<PalletEventAttr> = helper::take_item_attrs(&mut item.attrs)?;
+		let event_attrs: Vec<PalletEventAttr> = helper::take_item_pallet_attrs(&mut item.attrs)?;
 		let attr_info = PalletEventAttrInfo::from_attrs(event_attrs)?;
 		let metadata = attr_info.metadata.unwrap_or_else(Vec::new);
 		let deposit_event = attr_info.deposit_event;

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

@@ -47,7 +47,7 @@ pub trait MutItemAttrs {
 }
 
 /// Take the first pallet attribute (e.g. attribute like `#[pallet..]`) and decode it to `Attr`
-pub fn take_first_item_attr<Attr>(item: &mut impl MutItemAttrs) -> syn::Result<Option<Attr>> where
+pub fn take_first_item_pallet_attr<Attr>(item: &mut impl MutItemAttrs) -> syn::Result<Option<Attr>> where
 	Attr: syn::parse::Parse,
 {
 	let attrs = if let Some(attrs) = item.mut_item_attrs() {
@@ -69,18 +69,29 @@ pub fn take_first_item_attr<Attr>(item: &mut impl MutItemAttrs) -> syn::Result<O
 }
 
 /// Take all the pallet attributes (e.g. attribute like `#[pallet..]`) and decode them to `Attr`
-pub fn take_item_attrs<Attr>(item: &mut impl MutItemAttrs) -> syn::Result<Vec<Attr>> where
+pub fn take_item_pallet_attrs<Attr>(item: &mut impl MutItemAttrs) -> syn::Result<Vec<Attr>> where
 	Attr: syn::parse::Parse,
 {
 	let mut pallet_attrs = Vec::new();
 
-	while let Some(attr) = take_first_item_attr(item)? {
+	while let Some(attr) = take_first_item_pallet_attr(item)? {
 		pallet_attrs.push(attr)
 	}
 
 	Ok(pallet_attrs)
 }
 
+/// Get all the cfg attributes (e.g. attribute like `#[cfg..]`) and decode them to `Attr`
+pub fn get_item_cfg_attrs(attrs: &[syn::Attribute]) -> Vec<syn::Attribute> {
+	attrs.iter().filter_map(|attr|  {
+		if attr.path.segments.first().map_or(false, |segment| segment.ident == "cfg") {
+			Some(attr.clone())
+		} else {
+			None
+		}
+	}).collect::<Vec<_>>()
+}
+
 impl MutItemAttrs for syn::Item {
 	fn mut_item_attrs(&mut self) -> Option<&mut Vec<syn::Attribute>> {
 		match self {

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

@@ -89,7 +89,7 @@ impl Def {
 		let mut type_values = vec![];
 
 		for (index, item) in items.iter_mut().enumerate() {
-			let pallet_attr: Option<PalletAttr> = helper::take_first_item_attr(item)?;
+			let pallet_attr: Option<PalletAttr> = helper::take_first_item_pallet_attr(item)?;
 
 			match pallet_attr {
 				Some(PalletAttr::Config(span)) if config.is_none() =>

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

@@ -78,7 +78,7 @@ impl PalletStructDef {
 			return Err(syn::Error::new(item.span(), msg));
 		};
 
-		let mut event_attrs: Vec<PalletStructAttr> = helper::take_item_attrs(&mut item.attrs)?;
+		let mut event_attrs: Vec<PalletStructAttr> = helper::take_item_pallet_attrs(&mut item.attrs)?;
 		if event_attrs.len() > 1 {
 			let msg = "Invalid pallet::pallet, multiple argument pallet::generate_store found";
 			return Err(syn::Error::new(event_attrs[1].keyword.span(), msg));

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

@@ -91,6 +91,8 @@ pub struct StorageDef {
 	pub where_clause: Option<syn::WhereClause>,
 	/// The span of the pallet::storage attribute.
 	pub attr_span: proc_macro2::Span,
+	/// The `cfg` attributes.
+	pub cfg_attrs: Vec<syn::Attribute>,
 }
 
 /// In `Foo<A, B, C>` retrieve the argument at given position, i.e. A is argument at position 0.
@@ -125,13 +127,15 @@ impl StorageDef {
 			return Err(syn::Error::new(item.span(), "Invalid pallet::storage, expected item type"));
 		};
 
-		let mut attrs: Vec<PalletStorageAttr> = helper::take_item_attrs(&mut item.attrs)?;
+		let mut attrs: Vec<PalletStorageAttr> = helper::take_item_pallet_attrs(&mut item.attrs)?;
 		if attrs.len() > 1 {
 			let msg = "Invalid pallet::storage, multiple argument pallet::getter found";
 			return Err(syn::Error::new(attrs[1].getter.span(), msg));
 		}
 		let getter = attrs.pop().map(|attr| attr.getter);
 
+		let cfg_attrs = helper::get_item_cfg_attrs(&item.attrs);
+
 		let mut instances = vec![];
 		instances.push(helper::check_type_def_gen(&item.generics, item.ident.span())?);
 
@@ -223,6 +227,7 @@ impl StorageDef {
 			getter,
 			query_kind,
 			where_clause,
+			cfg_attrs,
 		})
 	}
 }