Introduce OrchardWallet::GetPotentialSpendsFromNullifier method.

src/rust/include/rust/orchard/wallet.h

@@ -333,6 +333,18 @@ void orchard_wallet_get_potential_spends(
         push_txid_callback_t push_cb
         );
 
+/**
+ * Returns a vector of transaction IDs for transactions that have been observed as
+ * spending the given nullifier by using the `push_cb` callback to push transaction
+ * IDs onto the provided result vector.
+ */
+void orchard_wallet_get_potential_spends_from_nullifier(
+        const OrchardWalletPtr* wallet,
+        const uint256& nullifier,
+        void* resultVector,
+        push_txid_callback_t push_cb
+        );
+
 /**
  * Fetches the information needed to spend the wallet note at the given outpoint,
  * relative to the current root known to the wallet of the Orchard commitment

src/rust/src/wallet.rs

@@ -1125,6 +1125,24 @@ pub extern "C" fn orchard_wallet_get_potential_spends(
     }
 }
 
+#[no_mangle]
+pub extern "C" fn orchard_wallet_get_potential_spends_from_nullifier(
+    wallet: *const Wallet,
+    nullifier: *const [c_uchar; 32],
+    result: Option<FFICallbackReceiver>,
+    push_cb: Option<PushTxId>,
+) {
+    let wallet = unsafe { wallet.as_ref() }.expect("Wallet pointer may not be null.");
+    let nullifier =
+        Nullifier::from_bytes(&*unsafe { nullifier.as_ref() }.expect("nullifier may not be null."));
+
+    if let Some(inpoints) = wallet.potential_spends.get(&nullifier.unwrap()) {
+        for inpoint in inpoints {
+            unsafe { (push_cb.unwrap())(result, inpoint.txid.as_ref()) };
+        }
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn orchard_wallet_get_spend_info(
     wallet: *const Wallet,

src/wallet/orchard.h

@@ -410,6 +410,17 @@ public:
         reinterpret_cast<std::vector<uint256>*>(txidsRet)->push_back(txid_out);
     }
 
+    std::vector<uint256> GetPotentialSpendsFromNullifier(const uint256& nullifier) const {
+        std::vector<uint256> result;
+        orchard_wallet_get_potential_spends_from_nullifier(
+            inner.get(),
+            nullifier,
+            &result,
+            PushTxId
+            );
+        return result;
+    }
+
     std::vector<uint256> GetPotentialSpends(const OrchardOutPoint& outPoint) const {
         std::vector<uint256> result;
         orchard_wallet_get_potential_spends(

src/wallet/wallet.cpp

@@ -1668,9 +1668,8 @@ set<uint256> CWallet::GetConflicts(const uint256& txid) const
         }
     }
 
-    for (uint32_t i = 0; i < wtx.GetOrchardBundle().GetNumActions(); i++) {
-        OrchardOutPoint op(wtx.GetHash(), i);
-        auto potential_spends = orchardWallet.GetPotentialSpends(op);
+    for (const uint256& nullifier : wtx.GetOrchardBundle().GetNullifiers()) {
+        auto potential_spends = orchardWallet.GetPotentialSpendsFromNullifier(nullifier);
 
         if (potential_spends.size() <= 1) {
             continue;  // No conflict if zero or one spends