Implements require_transactional (#7261)

* Implements require_transactional

* support wasm

* only enable for debug build

* remove wasm support and add feature flag

* Apply suggestions from code review

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

* only use check for debug_assertions

* update per review

* update docs

* Apply suggestions from code review

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

* remove duplicated tests

* fix test

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

substrate/frame/support/src/storage/mod.rs

@@ -30,6 +30,57 @@ pub mod child;
 pub mod generator;
 pub mod migration;
 
+#[cfg(all(feature = "std", any(test, debug_assertions)))]
+mod debug_helper {
+	use std::cell::RefCell;
+
+	thread_local! {
+		static TRANSACTION_LEVEL: RefCell<u32> = RefCell::new(0);
+	}
+
+	pub fn require_transaction() {
+		let level = TRANSACTION_LEVEL.with(|v| *v.borrow());
+		if level == 0 {
+			panic!("Require transaction not called within with_transaction");
+		}
+	}
+
+	pub struct TransactionLevelGuard;
+
+	impl Drop for TransactionLevelGuard {
+		fn drop(&mut self) {
+			TRANSACTION_LEVEL.with(|v| *v.borrow_mut() -= 1);
+		}
+	}
+
+	/// Increments the transaction level.
+	///
+	/// Returns a guard that when dropped decrements the transaction level automatically.
+	pub fn inc_transaction_level() -> TransactionLevelGuard {
+		TRANSACTION_LEVEL.with(|v| {
+			let mut val = v.borrow_mut();
+			*val += 1;
+			if *val > 10 {
+				crate::debug::warn!(
+					"Detected with_transaction with nest level {}. Nested usage of with_transaction is not recommended.",
+					*val
+				);
+			}
+		});
+
+		TransactionLevelGuard
+	}
+}
+
+/// Assert this method is called within a storage transaction.
+/// This will **panic** if is not called within a storage transaction.
+///
+/// This assertion is enabled for native execution and when `debug_assertions` are enabled.
+pub fn require_transaction() {
+	#[cfg(all(feature = "std", any(test, debug_assertions)))]
+	debug_helper::require_transaction();
+}
+
 /// Execute the supplied function in a new storage transaction.
 ///
 /// All changes to storage performed by the supplied function are discarded if the returned
@@ -43,6 +94,10 @@ pub fn with_transaction<R>(f: impl FnOnce() -> TransactionOutcome<R>) -> R {
 	use TransactionOutcome::*;
 
 	start_transaction();
+
+	#[cfg(all(feature = "std", any(test, debug_assertions)))]
+	let _guard = debug_helper::inc_transaction_level();
+
 	match f() {
 		Commit(res) => { commit_transaction(); res },
 		Rollback(res) => { rollback_transaction(); res },
@@ -732,4 +787,27 @@ mod test {
 			assert_eq!(Digest::decode(&mut &value[..]).unwrap(), expected);
 		});
 	}
+
+	#[test]
+	#[should_panic(expected = "Require transaction not called within with_transaction")]
+	fn require_transaction_should_panic() {
+		TestExternalities::default().execute_with(|| {
+			require_transaction();
+		});
+	}
+
+	#[test]
+	fn require_transaction_should_not_panic_in_with_transaction() {
+		TestExternalities::default().execute_with(|| {
+			with_transaction(|| {
+				require_transaction();
+				TransactionOutcome::Commit(())
+			});
+
+			with_transaction(|| {
+				require_transaction();
+				TransactionOutcome::Rollback(())
+			});
+		});
+	}
 }