TxGraph doesn't index null-prevout spends of non-coinbase txs, so their conflicts go undetected #2286

use bdk_chain::{local_chain::LocalChain, BlockId, TxGraph};
use bitcoin::{absolute, hashes::Hash, transaction, Amount, BlockHash, OutPoint, ScriptBuf,
              Transaction, TxIn, TxOut, Txid};

#[test]
fn null_prevout_conflicts_remain_canonical() {
    let mut graph = TxGraph::<BlockId>::default();
    for tag in [1u8, 2] {
        let tx = Transaction {
            version: transaction::Version::TWO,
            lock_time: absolute::LockTime::ZERO,
            input: [OutPoint::null(), OutPoint::new(Txid::from_byte_array([tag; 32]), 0)]
                .map(|previous_output| TxIn { previous_output, ..Default::default() })
                .to_vec(),
            output: vec![TxOut {
                value: Amount::from_sat(1),
                script_pubkey: ScriptBuf::new(),
            }],
        };
        assert!(!tx.is_coinbase());
        let _ = graph.insert_seen_at(tx.compute_txid(), u64::from(tag));
        let _ = graph.insert_tx(tx);
    }
    let chain = LocalChain::from_blocks(
        [(0, BlockHash::all_zeros())].into_iter().collect(),
    ).unwrap();
    let view = chain.canonical_view(&graph, chain.tip().block_id(), Default::default());
    let count = view.txs().len();
    assert!(count <= 1, "canonical spenders of null outpoint: {count}");
}