Fix storage expansion in pallet section (#6023)

fixes #5320 @sam0x17 @gupnik 

# Description

The issue could be confirmed with the added example. The cause is for
macro hygiene, `entries` in the `#( #entries_builder )*` expansion won't
be able to reference the `entries` defined outside. The solution here is
to allow the reference to be passed into the expansion with closure.

Or we could just switch to the unhygienic span with `quote::quote!`
instead such that `entries` will resolve to the "outer" definition.

prdoc/pr_6023.prdoc

@@ -0,0 +1,11 @@
+title: Fix storage in pallet section
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      Fix compilation of `pallet::storage` in a pallet section: a local binding definition was not
+      correctly referenced due to macro hygiene.
+
+crates:
+  - name: frame-support-procedural
+    bump: patch

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

@@ -427,15 +427,17 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 		};
 		entries_builder.push(quote::quote_spanned!(storage.attr_span =>
 			#(#cfg_attrs)*
-			{
-				<#full_ident as #frame_support::storage::StorageEntryMetadataBuilder>::build_metadata(
-					#deprecation,
-					#frame_support::__private::vec![
-						#( #docs, )*
-					],
-					&mut entries,
-				);
-			}
+			(|entries: &mut #frame_support::__private::Vec<_>| {
+				{
+					<#full_ident as #frame_support::storage::StorageEntryMetadataBuilder>::build_metadata(
+						#deprecation,
+						#frame_support::__private::vec![
+							#( #docs, )*
+						],
+						entries,
+					);
+				}
+			})
 		))
 	}
 
@@ -911,7 +913,7 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 					entries: {
 						#[allow(unused_mut)]
 						let mut entries = #frame_support::__private::vec![];
-						#( #entries_builder )*
+						#( #entries_builder(&mut entries); )*
 						entries
 					},
 				}

substrate/frame/support/test/tests/split_ui/pass/split_storage.rs

@@ -0,0 +1,49 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use frame_support::pallet_macros::import_section;
+
+mod storage;
+
+#[import_section(storage::storage)]
+#[frame_support::pallet(dev_mode)]
+pub mod pallet {
+    use frame_support::pallet_prelude::*;
+    use frame_system::pallet_prelude::*;
+
+    const STORAGE_VERSION: StorageVersion = StorageVersion::new(8);
+
+    #[pallet::pallet]
+    #[pallet::storage_version(STORAGE_VERSION)]
+    pub struct Pallet<T>(_);
+
+    #[pallet::config]
+    pub trait Config: frame_system::Config {}
+
+	#[pallet::call]
+	impl<T: Config> Pallet<T> {
+		pub fn increment_value(_origin: OriginFor<T>) -> DispatchResult {
+			Value::<T>::mutate(|v| {
+				v.saturating_add(1)
+			});
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/split_ui/pass/storage/mod.rs

@@ -0,0 +1,27 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use frame_support::pallet_macros::pallet_section;
+
+#[pallet_section]
+mod storage {
+	#[pallet::storage]
+	pub type Value<T> = StorageValue<_, u32, ValueQuery>;
+
+	#[pallet::storage]
+	pub type Map<T> = StorageMap<_, _, u32, u32, ValueQuery>;
+}