Merge bitcoindevkit#1473: Remove persist submodule

a0bf45b docs: remove PersistBackend from docs, Cargo.toml and wallet README.md (Steve Myers)
feb27df feat(chain)!: add `take` convenience method to `Append` trait (志宇)
1eca568 feat!: rm `persist` submodule (志宇)

Pull request description:

  ### Description

  @LLFourn suggested these changes which greatly simplifies the amount of code we have to maintain and removes the `async-trait` dependency. We remove `PersistBackend`, `PersistBackendAsync`, `StageExt` and `StageExtAsync` completely. Instead, we introduce `Wallet::take_staged(&mut self) -> Option<ChangeSet>`.

  The original intention to keep a staging area (`StageExt`, `StageExtAsync`) is to enforce:
  1. The caller will not persist an empty changeset.
  2. The caller does not take the staged changeset if the database (`PersistBackend`) fails.

  We achieve `1.` by returning `None` if the staged changeset is empty.

  `2.` is not too important. The caller can try figure out what to do with the changeset if persisting to db fails.

  ### Notes to the reviewers

  I added a `take` convenience method to the `Append` trait. I thought it would be handy for the caller to do a staging area with this.

  ### Changelog notice

  * Remove `persist` submodule from `bdk_chain`.
  * Change `Wallet` to outsource it's persistence logic by introducing `Wallet::take_staged`.
  * Add `take` convenience method to `Append` trait.

  ### 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:

  ~* [ ] I've added tests for the new feature~
  * [x] I've added docs for the new feature

ACKs for top commit:
  notmandatory:
    ACK a0bf45b
  evanlinjin:
    self-ACK a0bf45b

Tree-SHA512: 38939ab446c84d9baecd4cd36a7b66add5a121212ad5e06ade04a60f7903133dd9a20219e230ab8a40404c47e07b946ccd43085572d71c3a2a80240a2223a500

crates/chain/Cargo.toml

@@ -19,7 +19,6 @@ serde_crate = { package = "serde", version = "1", optional = true, features = ["
 # Use hashbrown as a feature flag to have HashSet and HashMap from it.
 hashbrown = { version = "0.9.1", optional = true, features = ["serde"] }
 miniscript = { version = "12.0.0", optional = true, default-features = false }
-async-trait = {  version = "0.1.80", optional = true }
 
 [dev-dependencies]
 rand = "0.8"
@@ -29,4 +28,3 @@ proptest = "1.2.0"
 default = ["std", "miniscript"]
 std = ["bitcoin/std", "miniscript?/std"]
 serde = ["serde_crate", "bitcoin/serde", "miniscript?/serde"]
-async = ["async-trait"]

crates/chain/src/changeset.rs

@@ -0,0 +1,89 @@
+/// A changeset containing [`crate`] structures typically persisted together.
+#[cfg(feature = "miniscript")]
+#[derive(Debug, Clone, PartialEq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(crate::serde::Deserialize, crate::serde::Serialize),
+    serde(
+        crate = "crate::serde",
+        bound(
+            deserialize = "A: Ord + crate::serde::Deserialize<'de>, K: Ord + crate::serde::Deserialize<'de>",
+            serialize = "A: Ord + crate::serde::Serialize, K: Ord + crate::serde::Serialize",
+        ),
+    )
+)]
+pub struct CombinedChangeSet<K, A> {
+    /// Changes to the [`LocalChain`](crate::local_chain::LocalChain).
+    pub chain: crate::local_chain::ChangeSet,
+    /// Changes to [`IndexedTxGraph`](crate::indexed_tx_graph::IndexedTxGraph).
+    pub indexed_tx_graph: crate::indexed_tx_graph::ChangeSet<A, crate::keychain::ChangeSet<K>>,
+    /// Stores the network type of the transaction data.
+    pub network: Option<bitcoin::Network>,
+}
+
+#[cfg(feature = "miniscript")]
+impl<K, A> core::default::Default for CombinedChangeSet<K, A> {
+    fn default() -> Self {
+        Self {
+            chain: core::default::Default::default(),
+            indexed_tx_graph: core::default::Default::default(),
+            network: None,
+        }
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl<K: Ord, A: crate::Anchor> crate::Append for CombinedChangeSet<K, A> {
+    fn append(&mut self, other: Self) {
+        crate::Append::append(&mut self.chain, other.chain);
+        crate::Append::append(&mut self.indexed_tx_graph, other.indexed_tx_graph);
+        if other.network.is_some() {
+            debug_assert!(
+                self.network.is_none() || self.network == other.network,
+                "network type must either be just introduced or remain the same"
+            );
+            self.network = other.network;
+        }
+    }
+
+    fn is_empty(&self) -> bool {
+        self.chain.is_empty() && self.indexed_tx_graph.is_empty() && self.network.is_none()
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl<K, A> From<crate::local_chain::ChangeSet> for CombinedChangeSet<K, A> {
+    fn from(chain: crate::local_chain::ChangeSet) -> Self {
+        Self {
+            chain,
+            ..Default::default()
+        }
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl<K, A> From<crate::indexed_tx_graph::ChangeSet<A, crate::keychain::ChangeSet<K>>>
+    for CombinedChangeSet<K, A>
+{
+    fn from(
+        indexed_tx_graph: crate::indexed_tx_graph::ChangeSet<A, crate::keychain::ChangeSet<K>>,
+    ) -> Self {
+        Self {
+            indexed_tx_graph,
+            ..Default::default()
+        }
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl<K, A> From<crate::keychain::ChangeSet<K>> for CombinedChangeSet<K, A> {
+    fn from(indexer: crate::keychain::ChangeSet<K>) -> Self {
+        Self {
+            indexed_tx_graph: crate::indexed_tx_graph::ChangeSet {
+                indexer,
+                ..Default::default()
+            },
+            ..Default::default()
+        }
+    }
+}

crates/chain/src/lib.rs

@@ -50,7 +50,8 @@ pub use descriptor_ext::{DescriptorExt, DescriptorId};
 mod spk_iter;
 #[cfg(feature = "miniscript")]
 pub use spk_iter::*;
-pub mod persist;
+mod changeset;
+pub use changeset::*;
 pub mod spk_client;
 
 #[allow(unused_imports)]