Merge #1533: [wallet] Enable support for single descriptor wallets

13e7008 doc(wallet): clarify docs for `Wallet::load` (valued mammal)
3951110 fix(wallet)!: Change method `LoadParams::descriptors` (valued mammal)
b802714 example(wallet): simplify miniscript compiler example (valued mammal)
2ca8b6f test(wallet): Add tests for single descriptor wallet (valued mammal)
31f1c2d fix(wallet): Change FromSql type to `Option<_>` (valued mammal)
75155b7 feat(wallet): Add method `Wallet::create_single` (valued mammal)

Pull request description:

  The change descriptor is made optional, making this an effective reversion of #1390 and enables creating wallets with a single descriptor.

  fixes #1511

  ### Notes to the reviewers

  PR 1390 also removed an error case [`ChangePolicyDescriptor`](https://github.com/bitcoindevkit/bdk/blob/8eef350bd08057acc39b6fc50b1217db5e29b968/crates/wallet/src/wallet/mod.rs#L1529-L1533) and this can possibly be added back. In the case the wallet only has a single descriptor we allow any utxos to fund a tx that aren't specifically marked unspendable regardless of the change spend policy.

  ### Changelog notice

  * Added method `Wallet::create_single` that expects a single `D: IntoWalletDescriptor` as input and enables building a wallet with no internal keychain.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [x] This pull request breaks the existing API
  * [x] I've added tests for the new feature
  * [x] I've added docs for the new feature

ACKs for top commit:
  evanlinjin:
    ACK 13e7008

Tree-SHA512: 3e6fe5d9165d62332ac1863ec769c4bc5c7cd3c7f3fbdb8f505906bcdc681fa73b3fef2571adb0e52e9a23d4257f66a6145838b90ec68596b5f4c64054a047fa

Author: evanlinjin

crates/chain/src/lib.rs

@@ -113,6 +113,13 @@ pub type KeychainIndexed<K, T> = ((K, u32), T);
 /// A wrapper that we use to impl remote traits for types in our crate or dependency crates.
 pub struct Impl<T>(pub T);
 
+impl<T> Impl<T> {
+    /// Returns the inner `T`.
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+}
+
 impl<T> From<T> for Impl<T> {
     fn from(value: T) -> Self {
         Self(value)

crates/wallet/README.md

@@ -79,8 +79,10 @@ let network = Network::Testnet;
 let descriptor = "wpkh(tprv8ZgxMBicQKsPdcAqYBpzAFwU5yxBUo88ggoBqu1qPcHUfSbKK1sKMLmC7EAk438btHQrSdu3jGGQa6PA71nvH5nkDexhLteJqkM4dQmWF9g/84'/1'/0'/0/*)";
 let change_descriptor = "wpkh(tprv8ZgxMBicQKsPdcAqYBpzAFwU5yxBUo88ggoBqu1qPcHUfSbKK1sKMLmC7EAk438btHQrSdu3jGGQa6PA71nvH5nkDexhLteJqkM4dQmWF9g/84'/1'/0'/1/*)";
 let wallet_opt = Wallet::load()
-    .descriptors(descriptor, change_descriptor)
     .network(network)
+    .descriptor(KeychainKind::External, Some(descriptor))
+    .descriptor(KeychainKind::Internal, Some(change_descriptor))
+    .extract_keys()
     .load_wallet(&mut db)
     .expect("wallet");
 let mut wallet = match wallet_opt {

crates/wallet/examples/compiler.rs

@@ -56,28 +56,8 @@ fn main() -> Result<(), Box<dyn Error>> {
 
     println!("Compiled into Descriptor: \n{}", descriptor);
 
-    // Do the same for another (internal) keychain
-    let policy_str = "or(
-        10@thresh(2,
-            pk(029ffbe722b147f3035c87cb1c60b9a5947dd49c774cc31e94773478711a929ac0),pk(025f05815e3a1a8a83bfbb03ce016c9a2ee31066b98f567f6227df1d76ec4bd143),pk(025625f41e4a065efc06d5019cbbd56fe8c07595af1231e7cbc03fafb87ebb71ec)
-        ),1@and(
-            pk(03deae92101c790b12653231439f27b8897264125ecb2f46f48278603102573165),
-            older(12960)
-        )
-    )"
-    .replace(&[' ', '\n', '\t'][..], "");
-
-    println!("Compiling internal policy: \n{}", policy_str);
-
-    let policy = Concrete::<String>::from_str(&policy_str)?;
-    let internal_descriptor = Descriptor::new_wsh(policy.compile()?)?.to_string();
-    println!(
-        "Compiled into internal Descriptor: \n{}",
-        internal_descriptor
-    );
-
     // Create a new wallet from descriptors
-    let mut wallet = Wallet::create(descriptor, internal_descriptor)
+    let mut wallet = Wallet::create_single(descriptor)
         .network(Network::Regtest)
         .create_wallet_no_persist()?;
 

crates/wallet/src/wallet/changeset.rs

@@ -103,16 +103,18 @@ impl ChangeSet {
         let row = wallet_statement
             .query_row([], |row| {
                 Ok((
-                    row.get::<_, Impl<Descriptor<DescriptorPublicKey>>>("descriptor")?,
-                    row.get::<_, Impl<Descriptor<DescriptorPublicKey>>>("change_descriptor")?,
-                    row.get::<_, Impl<bitcoin::Network>>("network")?,
+                    row.get::<_, Option<Impl<Descriptor<DescriptorPublicKey>>>>("descriptor")?,
+                    row.get::<_, Option<Impl<Descriptor<DescriptorPublicKey>>>>(
+                        "change_descriptor",
+                    )?,
+                    row.get::<_, Option<Impl<bitcoin::Network>>>("network")?,
                 ))
             })
             .optional()?;
-        if let Some((Impl(desc), Impl(change_desc), Impl(network))) = row {
-            changeset.descriptor = Some(desc);
-            changeset.change_descriptor = Some(change_desc);
-            changeset.network = Some(network);
+        if let Some((desc, change_desc, network)) = row {
+            changeset.descriptor = desc.map(Impl::into_inner);
+            changeset.change_descriptor = change_desc.map(Impl::into_inner);
+            changeset.network = network.map(Impl::into_inner);
         }
 
         changeset.local_chain = local_chain::ChangeSet::from_sqlite(db_tx)?;