mesh-1269: enforce no dupe did tax

pallets/corporate-actions/src/lib.rs

@@ -384,6 +384,15 @@ decl_module! {
             let next_id = local_id.0.checked_add(1).map(LocalCAId).ok_or(Error::<T>::LocalCAIdOverflow)?;
             let id = CAId { ticker, local_id };
 
+            // Ensure there are no duplicates in withholding tax overrides.
+            let mut wt = wt;
+            if let Some(wt) = &mut wt {
+                let before = wt.len();
+                wt.sort_unstable_by_key(|&(did, _)| did);
+                wt.dedup_by_key(|&mut (did, _)| did);
+                ensure!(before == wt.len(), Error::<T>::DuplicateDidTax);
+            }
+
             // Create a checkpoint at `record_date`, if any.
             if let Some(record_date) = record_date {
                 <Asset<T>>::_create_checkpoint_emit(ticker, record_date, caa)?;
@@ -397,15 +406,7 @@ decl_module! {
                 .map(|t| t.dedup())
                 .unwrap_or_else(|| Self::default_target_identities(ticker));
             let dwt = default_wt.unwrap_or_else(|| Self::default_withholding_tax(ticker));
-            let wt = match wt {
-                None => Self::did_withholding_tax(ticker),
-                Some(mut wt) => {
-                    // Nuke duplicates.
-                    wt.sort_unstable_by_key(|&(did, _)| did);
-                    wt.dedup_by_key(|&mut (did, _)| did);
-                    wt
-                },
-            };
+            let wt = wt.unwrap_or_else(|| Self::did_withholding_tax(ticker));
 
             // Commit CA to storage.
             CorporateActions::insert(ticker, id.local_id, CorporateAction {
@@ -467,6 +468,9 @@ decl_error! {
         /// There have been too many CAs for this ticker and the ID would overflow.
         /// This won't occur in practice.
         LocalCAIdOverflow,
+        /// A withholding tax override for a given DID was specified more than once.
+        /// The chain refused to make a choice, and hence there was an error.
+        DuplicateDidTax,
     }
 }
 

pallets/runtime/tests/src/corporate_actions_test.rs

@@ -463,6 +463,15 @@ fn initiate_corporate_action_did_tax() {
     });
 }
 
+#[test]
+#[should_panic]
+fn initiate_corporate_action_did_tax_dupe() {
+    test(|ticker, [owner, foo, bar]| {
+        let wt = Some(vec![(bar.did, P75), (foo.did, P0), (bar.did, P50)]);
+        basic_ca(owner, ticker, None, None, wt);
+    });
+}
+
 #[test]
 fn initiate_corporate_action_targets() {
     test(|ticker, [owner, foo, bar]| {