feat(aztec-nr): add EphemeralArray::empty_at constructor (#23839)

Author: nchamo

noir-projects/aztec-nr/aztec/src/ephemeral/mod.nr

@@ -30,6 +30,11 @@ impl<T> EphemeralArray<T> {
         Self { slot }
     }
 
+    /// Returns an empty ephemeral array at the given slot, clearing any pre-existing data.
+    pub unconstrained fn empty_at(slot: Field) -> Self {
+        Self::at(slot).clear()
+    }
+
     /// Returns the number of elements stored in the array.
     pub unconstrained fn len(self) -> u32 {
         ephemeral::len_oracle(self.slot)
@@ -76,8 +81,9 @@ impl<T> EphemeralArray<T> {
         ephemeral::remove_oracle(self.slot, index);
     }
 
-    /// Removes all elements from the array and returns self for chaining (e.g. `EphemeralArray::at(slot).clear()`
-    /// to get a guaranteed-empty array at a given slot).
+    /// Removes all elements from the array and returns self for chaining.
+    ///
+    /// Prefer [`EphemeralArray::empty_at`] when the intent is to start with a fresh array.
     pub unconstrained fn clear(self) -> Self {
         ephemeral::clear_oracle(self.slot);
         self
@@ -362,6 +368,19 @@ mod test {
         });
     }
 
+    #[test]
+    unconstrained fn empty_at_wipes_previous_data() {
+        let env = TestEnvironment::new();
+        env.utility_context(|_| {
+            let array: EphemeralArray<Field> = EphemeralArray::at(SLOT);
+            array.push(1);
+            assert_eq(array.len(), 1);
+
+            let fresh: EphemeralArray<Field> = EphemeralArray::empty_at(SLOT);
+            assert_eq(fresh.len(), 0);
+        });
+    }
+
     #[test]
     unconstrained fn clear_returns_self() {
         let env = TestEnvironment::new();

noir-projects/aztec-nr/aztec/src/messages/discovery/mod.nr

@@ -146,7 +146,7 @@ pub unconstrained fn do_sync_state(
     // First we process all private logs, which can contain different kinds of messages e.g. private notes, partial
     // notes, private events, etc.
     // TODO(F-588): populate with tagging secrets for constrained delivery
-    let provided_secrets = EphemeralArray::<ProvidedSecret>::at(PROVIDED_SECRETS_ARRAY_BASE_SLOT).clear();
+    let provided_secrets = EphemeralArray::<ProvidedSecret>::empty_at(PROVIDED_SECRETS_ARRAY_BASE_SLOT);
     let logs = message_processing::get_pending_tagged_logs(scope, provided_secrets);
     logs.for_each(|_i, pending_tagged_log: PendingTaggedLog| {
         if pending_tagged_log.log.len() == 0 {

noir-projects/aztec-nr/aztec/src/messages/processing/offchain.nr

@@ -141,9 +141,9 @@ pub unconstrained fn sync_inbox(
     scope: AztecAddress,
 ) -> EphemeralArray<OffchainMessageWithContext> {
     let inbox: CapsuleArray<PendingOffchainMsg> = CapsuleArray::at(contract_address, OFFCHAIN_INBOX_SLOT, scope);
-    let context_resolution_requests: EphemeralArray<Field> = EphemeralArray::at(OFFCHAIN_CONTEXT_REQUESTS_SLOT).clear();
+    let context_resolution_requests: EphemeralArray<Field> = EphemeralArray::empty_at(OFFCHAIN_CONTEXT_REQUESTS_SLOT);
     let ready_to_process: EphemeralArray<OffchainMessageWithContext> =
-        EphemeralArray::at(OFFCHAIN_READY_MESSAGES_SLOT).clear();
+        EphemeralArray::empty_at(OFFCHAIN_READY_MESSAGES_SLOT);
 
     // Build a request list aligned with the inbox indices.
     let mut i = 0;

noir-projects/aztec-nr/aztec/src/oracle/shared_secret.nr

@@ -43,7 +43,7 @@ pub unconstrained fn get_shared_secrets<let N: u32>(
     eph_pks: BoundedVec<EmbeddedCurvePoint, N>,
     contract_address: AztecAddress,
 ) -> BoundedVec<Field, N> {
-    let request_array: EphemeralArray<EmbeddedCurvePoint> = EphemeralArray::at(GET_SHARED_SECRETS_REQUEST_SLOT).clear();
+    let request_array: EphemeralArray<EmbeddedCurvePoint> = EphemeralArray::empty_at(GET_SHARED_SECRETS_REQUEST_SLOT);
     eph_pks.for_each(|pk| request_array.push(pk));
 
     let response_array = get_shared_secrets_oracle(address, request_array, contract_address);

noir-projects/noir-contracts/contracts/standard/handshake_registry_contract/src/sync.nr

@@ -109,7 +109,7 @@ unconstrained fn get_handshake_logs_in_range(
     from_block: Option<u32>,
     to_block: Option<u32>,
 ) -> EphemeralArray<LogRetrievalResponse> {
-    let requests = EphemeralArray::at(LOG_RETRIEVAL_REQUEST_ARRAY_SLOT).clear();
+    let requests = EphemeralArray::empty_at(LOG_RETRIEVAL_REQUEST_ARRAY_SLOT);
     requests.push(
         LogRetrievalRequest {
             contract_address,