remove pallet::getter from pallet-offences (#6027)

# Description
Part of #3326
Removes pallet::getter from pallet-offences from type `Reports`.
Adds a test to verify that retrieval of `Reports` still works with
storage::getter.

polkadot address: 155YyFVoMnv9BY6qxy2i5wxtveUw7WE1n5H81fL8PZKTA1Sd

---------

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Dónal Murray <donal.murray@parity.io>

prdoc/pr_6027.prdoc

@@ -0,0 +1,9 @@
+title: Remove pallet::getter from pallet-offences
+doc:
+  - audience: Runtime Dev
+    description: |
+      This PR removes pallet::getter from pallet-offences from type Reports. It also adds a test to verify that retrieval of Reports still works with storage::getter.
+
+crates:
+  - name: pallet-offences
+    bump: patch

substrate/frame/offences/src/lib.rs

@@ -73,7 +73,6 @@ pub mod pallet {
 
 	/// The primary structure that holds all offence records keyed by report identifiers.
 	#[pallet::storage]
-	#[pallet::getter(fn reports)]
 	pub type Reports<T: Config> = StorageMap<
 		_,
 		Twox64Concat,
@@ -152,6 +151,13 @@ where
 }
 
 impl<T: Config> Pallet<T> {
+	/// Get the offence details from reports of given ID.
+	pub fn reports(
+		report_id: ReportIdOf<T>,
+	) -> Option<OffenceDetails<T::AccountId, T::IdentificationTuple>> {
+		Reports::<T>::get(report_id)
+	}
+
 	/// Compute the ID for the given report properties.
 	///
 	/// The report id depends on the offence kind, time slot and the id of offender.

substrate/frame/offences/src/tests.rs

@@ -21,12 +21,34 @@
 
 use super::*;
 use crate::mock::{
-	new_test_ext, offence_reports, with_on_offence_fractions, Offence, Offences, RuntimeEvent,
-	System, KIND,
+	new_test_ext, offence_reports, with_on_offence_fractions, Offence, Offences, Runtime,
+	RuntimeEvent, System, KIND,
 };
 use frame_system::{EventRecord, Phase};
+use sp_core::H256;
 use sp_runtime::Perbill;
 
+#[test]
+fn should_get_reports_with_storagemap_getter_and_function_getter() {
+	new_test_ext().execute_with(|| {
+		// given
+		let report_id: ReportIdOf<Runtime> = H256::from_low_u64_be(1);
+		let offence_details = OffenceDetails { offender: 1, reporters: vec![2, 3] };
+
+		Reports::<Runtime>::insert(report_id, offence_details.clone());
+
+		// when
+		let stored_offence_details = Offences::reports(report_id);
+		// then
+		assert_eq!(stored_offence_details, Some(offence_details.clone()));
+
+		// when
+		let stored_offence_details = Reports::<Runtime>::get(report_id);
+		// then
+		assert_eq!(stored_offence_details, Some(offence_details.clone()));
+	});
+}
+
 #[test]
 fn should_report_an_authority_and_trigger_on_offence() {
 	new_test_ext().execute_with(|| {