Incrementable: return None instead of saturating (#7846)

Closes #7845

---------

Co-authored-by: cmd[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Guillaume Thiolliere <guillaume.thiolliere@parity.io>

prdoc/pr_7846.prdoc

+title: 'Incrementable: return None instead of saturating'
+doc:
+- audience:
+  - Runtime Dev
+  - Runtime User
+  description: 'Fix implementation to follow the trait specification more closely. Closes #7845 '
+crates:
+- name: frame-support
+  bump: patch

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

@@ -25,7 +25,7 @@ use scale_info::TypeInfo;
 pub use sp_core::storage::TrackedStorageKey;
 use sp_core::Get;
 use sp_runtime::{
-	traits::{Convert, Member, Saturating},
+	traits::{Convert, Member},
 	DispatchError, RuntimeDebug,
 };
 
@@ -292,9 +292,7 @@ macro_rules! impl_incrementable {
 		$(
 			impl Incrementable for $type {
 				fn increment(&self) -> Option<Self> {
-					let mut val = self.clone();
-					val.saturating_inc();
-					Some(val)
+					self.checked_add(1)
 				}
 
 				fn initial_value() -> Option<Self> {
@@ -332,6 +330,14 @@ mod tests {
 	use crate::BoundedVec;
 	use sp_core::{ConstU32, ConstU64};
 
+	#[test]
+	fn incrementable_works() {
+		assert_eq!(0u8.increment(), Some(1));
+		assert_eq!(1u8.increment(), Some(2));
+
+		assert_eq!(u8::MAX.increment(), None);
+	}
+
 	#[test]
 	fn linear_storage_price_works() {
 		type Linear = LinearStoragePrice<ConstU64<7>, ConstU64<3>, u64>;