Introduce keychain::LocalChangeSet

This corresponds to `keychain::KeychainChangeSet` but for the redesigned
structures with `LocalChain`.

This structure is now used in `Wallet` as well as the examples.

crates/chain/src/indexed_tx_graph.rs

@@ -2,6 +2,7 @@ use alloc::vec::Vec;
 use bitcoin::{OutPoint, Transaction, TxOut};
 
 use crate::{
+    keychain::DerivationAdditions,
     tx_graph::{Additions, TxGraph},
     Anchor, Append,
 };
@@ -212,6 +213,15 @@ impl<A, IA: Default> From<Additions<A>> for IndexedAdditions<A, IA> {
     }
 }
 
+impl<A, K> From<DerivationAdditions<K>> for IndexedAdditions<A, DerivationAdditions<K>> {
+    fn from(index_additions: DerivationAdditions<K>) -> Self {
+        Self {
+            graph_additions: Default::default(),
+            index_additions,
+        }
+    }
+}
+
 /// Represents a structure that can index transaction data.
 pub trait Indexer {
     /// The resultant "additions" when new transaction data is indexed.

crates/chain/src/keychain.rs

@@ -18,10 +18,11 @@
 use crate::{
     chain_graph::{self, ChainGraph},
     collections::BTreeMap,
-    local_chain::LocalChain,
+    indexed_tx_graph::IndexedAdditions,
+    local_chain::{self, LocalChain},
     sparse_chain::ChainPosition,
     tx_graph::TxGraph,
-    Append, ForEachTxOut,
+    Anchor, Append, ForEachTxOut,
 };
 
 #[cfg(feature = "miniscript")]
@@ -125,6 +126,67 @@ impl<K, A> Default for LocalUpdate<K, A> {
     }
 }
 
+/// A structure that records the corresponding changes as result of applying an [`LocalUpdate`].
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(
+        crate = "serde_crate",
+        bound(
+            deserialize = "K: Ord + serde::Deserialize<'de>, A: Ord + serde::Deserialize<'de>",
+            serialize = "K: Ord + serde::Serialize, A: Ord + serde::Serialize",
+        )
+    )
+)]
+pub struct LocalChangeSet<K, A> {
+    /// Changes to the [`LocalChain`].
+    pub chain_changeset: local_chain::ChangeSet,
+
+    /// Additions to [`IndexedTxGraph`].
+    ///
+    /// [`IndexedTxGraph`]: crate::indexed_tx_graph::IndexedTxGraph
+    pub indexed_additions: IndexedAdditions<A, DerivationAdditions<K>>,
+}
+
+impl<K, A> Default for LocalChangeSet<K, A> {
+    fn default() -> Self {
+        Self {
+            chain_changeset: Default::default(),
+            indexed_additions: Default::default(),
+        }
+    }
+}
+
+impl<K: Ord, A: Anchor> Append for LocalChangeSet<K, A> {
+    fn append(&mut self, other: Self) {
+        Append::append(&mut self.chain_changeset, other.chain_changeset);
+        Append::append(&mut self.indexed_additions, other.indexed_additions);
+    }
+
+    fn is_empty(&self) -> bool {
+        self.chain_changeset.is_empty() && self.indexed_additions.is_empty()
+    }
+}
+
+impl<K, A> From<local_chain::ChangeSet> for LocalChangeSet<K, A> {
+    fn from(chain_changeset: local_chain::ChangeSet) -> Self {
+        Self {
+            chain_changeset,
+            ..Default::default()
+        }
+    }
+}
+
+impl<K, A> From<IndexedAdditions<A, DerivationAdditions<K>>> for LocalChangeSet<K, A> {
+    fn from(indexed_additions: IndexedAdditions<A, DerivationAdditions<K>>) -> Self {
+        Self {
+            indexed_additions,
+            ..Default::default()
+        }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq)]
 /// An update that includes the last active indexes of each keychain.
 pub struct KeychainScan<K, P> {