Add lock time types

Add a `LockTime` type to hold the nLockTime `u32` value. Use it in
`Transaction` for `lock_time` instead of a `u32`. Make it public so this
new type can be used by rust-miniscript and other downstream projects.

Add a `PackedLockTime` type that wraps a raw `u32` and derives `Ord`,
this type is for wrapping a consensus lock time value for nesting in
types that would like to derive `Ord`.

examples/ecdsa-psbt.rs

@@ -43,8 +43,8 @@ use bitcoin::util::bip32::{
 };
 use bitcoin::util::psbt::{self, Input, Psbt, PsbtSighashType};
 use bitcoin::{
-    Address, Amount, Network, OutPoint, PrivateKey, PublicKey, Script, Sequence, Transaction, TxIn,
-    TxOut, Txid, Witness,
+    Address, Amount, Network, OutPoint, PackedLockTime, PrivateKey, PublicKey, Script, Sequence,
+    Transaction, TxIn, TxOut, Txid, Witness,
 };
 
 use self::psbt_sign::*;
@@ -207,7 +207,7 @@ impl WatchOnly {
 
         let tx = Transaction {
             version: 2,
-            lock_time: 0,
+            lock_time: PackedLockTime::ZERO,
             input: vec![TxIn {
                 previous_output: OutPoint {
                     txid: Txid::from_hex(INPUT_UTXO_TXID)?,

src/blockdata/constants.rs

@@ -16,6 +16,7 @@ use crate::hashes::hex::{self, HexIterator};
 use crate::hashes::{Hash, sha256d};
 use crate::blockdata::opcodes;
 use crate::blockdata::script;
+use crate::blockdata::locktime::PackedLockTime;
 use crate::blockdata::transaction::{OutPoint, Transaction, TxOut, TxIn, Sequence};
 use crate::blockdata::block::{Block, BlockHeader};
 use crate::blockdata::witness::Witness;
@@ -73,7 +74,7 @@ fn bitcoin_genesis_tx() -> Transaction {
     // Base
     let mut ret = Transaction {
         version: 1,
-        lock_time: 0,
+        lock_time: PackedLockTime::ZERO,
         input: vec![],
         output: vec![],
     };
@@ -201,6 +202,7 @@ mod test {
     use crate::hashes::hex::{ToHex, FromHex};
     use crate::network::constants::Network;
     use crate::consensus::encode::serialize;
+    use crate::blockdata::locktime::PackedLockTime;
 
     #[test]
     fn bitcoin_genesis_first_transaction() {
@@ -218,7 +220,7 @@ mod test {
         assert_eq!(serialize(&gen.output[0].script_pubkey),
                    Vec::from_hex("434104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac").unwrap());
         assert_eq!(gen.output[0].value, 50 * COIN_VALUE);
-        assert_eq!(gen.lock_time, 0);
+        assert_eq!(gen.lock_time, PackedLockTime::ZERO);
 
         assert_eq!(gen.wtxid().to_hex(), "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b");
     }