Update `has_inputs_and_outputs()` for new consensus rules (#2398)

* update the has_inputs_and_outputs() to new rules

* apply clippy suggestions

* add some TODOs

zebra-chain/src/transaction.rs

@@ -483,4 +483,11 @@ impl Transaction {
             .map(orchard::ShieldedData::nullifiers)
             .flatten()
     }
+
+    /// Access the [`orchard::Flags`] in this transaction, if there is any,
+    /// regardless of version.
+    pub fn orchard_flags(&self) -> Option<orchard::shielded_data::Flags> {
+        self.orchard_shielded_data()
+            .map(|orchard_shielded_data| orchard_shielded_data.flags)
+    }
 }

zebra-consensus/src/transaction/check.rs

@@ -13,12 +13,14 @@ use crate::error::TransactionError;
 /// Checks that the transaction has inputs and outputs.
 ///
 /// For `Transaction::V4`:
-/// * at least one of `tx_in_count`, `nSpendsSapling`, and `nJoinSplit` MUST be non-zero.
-/// * at least one of `tx_out_count`, `nOutputsSapling`, and `nJoinSplit` MUST be non-zero.
+/// * At least one of `tx_in_count`, `nSpendsSapling`, and `nJoinSplit` MUST be non-zero.
+/// * At least one of `tx_out_count`, `nOutputsSapling`, and `nJoinSplit` MUST be non-zero.
 ///
 /// For `Transaction::V5`:
-/// * at least one of `tx_in_count`, `nSpendsSapling`, and `nActionsOrchard` MUST be non-zero.
-/// * at least one of `tx_out_count`, `nOutputsSapling`, and `nActionsOrchard` MUST be non-zero.
+/// * This condition must hold: `tx_in_count` > 0 or `nSpendsSapling` > 0 or
+/// (`nActionsOrchard` > 0 and `enableSpendsOrchard` = 1)
+/// * This condition must hold: `tx_out_count` > 0 or `nOutputsSapling` > 0 or
+/// (`nActionsOrchard` > 0 and `enableOutputsOrchard` = 1)
 ///
 /// This check counts both `Coinbase` and `PrevOut` transparent inputs.
 ///
@@ -30,10 +32,22 @@ pub fn has_inputs_and_outputs(tx: &Transaction) -> Result<(), TransactionError>
     let n_spends_sapling = tx.sapling_spends_per_anchor().count();
     let n_outputs_sapling = tx.sapling_outputs().count();
     let n_actions_orchard = tx.orchard_actions().count();
+    let flags_orchard = tx.orchard_flags().unwrap_or_else(Flags::empty);
 
-    if tx_in_count + n_spends_sapling + n_joinsplit + n_actions_orchard == 0 {
+    // TODO: Improve the code to express the spec rules better #2410.
+    if tx_in_count
+        + n_spends_sapling
+        + n_joinsplit
+        + (n_actions_orchard > 0 && flags_orchard.contains(Flags::ENABLE_SPENDS)) as usize
+        == 0
+    {
         Err(TransactionError::NoInputs)
-    } else if tx_out_count + n_outputs_sapling + n_joinsplit + n_actions_orchard == 0 {
+    } else if tx_out_count
+        + n_outputs_sapling
+        + n_joinsplit
+        + (n_actions_orchard > 0 && flags_orchard.contains(Flags::ENABLE_OUTPUTS)) as usize
+        == 0
+    {
         Err(TransactionError::NoOutputs)
     } else {
         Ok(())

zebra-consensus/src/transaction/tests.rs

@@ -86,8 +86,35 @@ fn fake_v5_transaction_with_orchard_actions_has_inputs_and_outputs() {
     // guaranteed structurally by `orchard::ShieldedData`)
     insert_fake_orchard_shielded_data(&mut transaction);
 
-    // If a transaction has at least one Orchard shielded action, it should be considered to have
-    // inputs and/or outputs
+    // The check will fail if the transaction has no flags
+    assert_eq!(
+        check::has_inputs_and_outputs(&transaction),
+        Err(TransactionError::NoInputs)
+    );
+
+    // If we add ENABLE_SPENDS flag it will pass the inputs check but fails with the outputs
+    // TODO: Avoid new calls to `insert_fake_orchard_shielded_data` for each check #2409.
+    let shielded_data = insert_fake_orchard_shielded_data(&mut transaction);
+    shielded_data.flags = orchard::Flags::ENABLE_SPENDS;
+
+    assert_eq!(
+        check::has_inputs_and_outputs(&transaction),
+        Err(TransactionError::NoOutputs)
+    );
+
+    // If we add ENABLE_OUTPUTS flag it will pass the outputs check but fails with the inputs
+    let shielded_data = insert_fake_orchard_shielded_data(&mut transaction);
+    shielded_data.flags = orchard::Flags::ENABLE_OUTPUTS;
+
+    assert_eq!(
+        check::has_inputs_and_outputs(&transaction),
+        Err(TransactionError::NoInputs)
+    );
+
+    // Finally make it valid by adding both required flags
+    let shielded_data = insert_fake_orchard_shielded_data(&mut transaction);
+    shielded_data.flags = orchard::Flags::ENABLE_SPENDS | orchard::Flags::ENABLE_OUTPUTS;
+
     assert!(check::has_inputs_and_outputs(&transaction).is_ok());
 }