Apply suggestions from code review

Co-authored-by: Marek <[email protected]>

zebra-consensus/src/transaction.rs

@@ -611,14 +611,13 @@ where
     /// Waits for the UTXOs that are being spent by the given transaction to arrive in
     /// the state for [`Block`](Request::Block) requests.
     ///
-    /// `known_utxos` are additional UTXOs known at the time of validation (i.e.
-    /// from previous transactions in the block).
-    ///
     /// Looks up UTXOs that are being spent by the given transaction in the state or waits
     /// for them to be added to the mempool for [`Mempool`](Request::Mempool) requests.
     ///
-    /// Returns a tuple with a OutPoint -> Utxo map, and a vector of Outputs
-    /// in the same order as the matching inputs in the transaction.
+    /// Returns a triple containing:
+    /// - `OutPoint` -> `Utxo` map, 
+    /// - vec of `Output`s in the same order as the matching inputs in the `tx`,
+    /// - vec of `Outpoint`s spent by a mempool `tx` that were not found in the best chain's utxo set.
     async fn spent_utxos(
         tx: Arc<Transaction>,
         req: Request,
@@ -633,6 +632,8 @@ where
         TransactionError,
     > {
         let is_mempool = req.is_mempool();
+        // Additional UTXOs known at the time of validation,
+        // i.e., from previous transactions in the block.
         let known_utxos = req.known_utxos();
 
         let inputs = tx.inputs();

zebra-node-services/src/mempool/transaction_dependencies.rs

@@ -7,7 +7,7 @@ use zebra_chain::{transaction, transparent};
 /// Representation of mempool transactions' dependencies on other transactions in the mempool.
 #[derive(Default, Debug, Clone)]
 pub struct TransactionDependencies {
-    /// Lists of mempool transactions that create UTXOs spent by
+    /// Lists of mempool transaction ids that create UTXOs spent by
     /// a mempool transaction. Used during block template construction
     /// to exclude transactions from block templates unless all of the
     /// transactions they depend on have been included.

zebra-rpc/src/methods/get_block_template_rpcs/zip317.rs

@@ -198,6 +198,10 @@ fn has_direct_dependencies(
         return true;
     };
 
+if selected_txs.len() < deps.len() {
+    return false;
+}
+
     let mut num_available_deps = 0;
     for tx in selected_txs {
         #[cfg(test)]
@@ -291,6 +295,12 @@ fn checked_add_transaction_weighted_random(
         let mut next_level_dependents = HashSet::new();
 
         for dependent_tx_id in &current_level_dependents {
+            // ## Note
+            //
+            // A necessary condition for adding the dependent tx is that it spends unmined outputs coming only from
+            // the selected txs, which come from the mempool. If the tx also spends in-chain outputs, it won't
+            // be added. This behavior is not specified by consensus rules and can be changed at any time,
+            // meaning that such txs could be added.
             if has_direct_dependencies(tx_dependencies.get(dependent_tx_id), selected_txs) {
                 let Some(candidate_tx) = dependent_txs.remove(dependent_tx_id) else {
                     continue;