Add coinbase shielded descriptions check

zebra-consensus/src/transaction.rs

@@ -55,6 +55,8 @@ pub enum VerifyTransactionError {
     NoTransfer,
     /// The balance of money moving around doesn't compute.
     BadBalance,
+    /// Violation of coinbase rules.
+    Coinbase,
     /// Could not verify a transparent script
     Script(#[from] zebra_script::Error),
     /// Could not verify a Groth16 proof of a JoinSplit/Spend/Output description
@@ -148,6 +150,7 @@ where
                     #[allow(clippy::if_same_then_else)] // delete when filled in
                     if tx.is_coinbase() {
                         // do something special for coinbase transactions
+                        check::coinbase_tx_does_not_spend_shielded(&tx)?;
                     } else {
                         // otherwise, check no coinbase inputs
                         // feed all of the inputs to the script verifier

zebra-consensus/src/transaction/check.rs

@@ -92,3 +92,27 @@ pub fn shielded_balances_match(
         return Err(VerifyTransactionError::BadBalance);
     }
 }
+
+/// Check that a coinbase tx does not have any JoinSplit or Spend descriptions.
+///
+/// https://zips.z.cash/protocol/canopy.pdf#consensusfrombitcoin
+pub fn coinbase_tx_does_not_spend_shielded(tx: &Transaction) -> Result<(), VerifyTransactionError> {
+    match tx {
+        Transaction::V4 {
+            joinsplit_data: Some(joinsplit_data),
+            shielded_data: Some(shielded_data),
+            ..
+        } => {
+            if !tx.is_coinbase() {
+                return Ok(());
+            } else if joinsplit_data.joinsplits().count() == 0
+                && shielded_data.spends().count() == 0
+            {
+                return Ok(());
+            } else {
+                return Err(VerifyTransactionError::Coinbase);
+            }
+        }
+        _ => return Err(VerifyTransactionError::WrongVersion),
+    }
+}