Merge #1387: fix(wallet): remove the generic from wallet

e51af49 fix(wallet): remove generic from wallet (Rob N)

Pull request description:

  ### Description

  The `PersistenceBackend` uses generics to describe errors returned while applying the change set to the persistence layer. This change removes generics wherever possible and introduces a new public error enum. Removing the generics from `PersistenceBackend` errors is the first step towards #1363

  *Update*: I proceeded with removing the generics from `Wallet` by introducing a `Box<dyn PersistenceBackend>` .

  ### Notes to the reviewers

  This one sort of blew up in the number of changes due to the use of generics for most of the `Wallet` error variants. The generics were only used for the persistence errors, so I removed the generics from higher level errors whenever possible. The error variants of `PersistenceBackend` may also be more expressive, but I will level that up for discussion and make any changes required.

  ### Changelog notice

  - Changed `PersistenceBackend` errors to depend on the `anyhow` crate.
  - Remove the generic `T` from `Wallet`

  ### 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

  #### Bugfixes:

  * [x] This pull request breaks the existing API
  * [ ] I've added tests to reproduce the issue which are now passing
  * [x] I'm linking the issue being fixed by this PR

ACKs for top commit:
  evanlinjin:
    ACK e51af49

Tree-SHA512: 8ce4f1c495310e16145555f4a6a29a0f42cf8944eda68004595c3532580767f64f779185022147a00d75001c40d69fdf8f8de2d348eb68484b170d2a181117ff

crates/bdk/Cargo.toml

@@ -13,6 +13,7 @@ edition = "2021"
 rust-version = "1.63"
 
 [dependencies]
+anyhow = { version = "1", default-features = false }
 rand = "^0.8"
 miniscript = { version = "11.0.0", features = ["serde"], default-features = false }
 bitcoin = { version = "0.31.0", features = ["serde", "base64", "rand-std"], default-features = false }

crates/bdk/src/wallet/error.rs

@@ -47,11 +47,11 @@ impl std::error::Error for MiniscriptPsbtError {}
 /// Error returned from [`TxBuilder::finish`]
 ///
 /// [`TxBuilder::finish`]: crate::wallet::tx_builder::TxBuilder::finish
-pub enum CreateTxError<P> {
+pub enum CreateTxError {
     /// There was a problem with the descriptors passed in
     Descriptor(DescriptorError),
-    /// We were unable to write wallet data to the persistence backend
-    Persist(P),
+    /// We were unable to load wallet data from or write wallet data to the persistence backend
+    Persist(anyhow::Error),
     /// There was a problem while extracting and manipulating policies
     Policy(PolicyError),
     /// Spending policy is not compatible with this [`KeychainKind`]
@@ -119,17 +119,14 @@ pub enum CreateTxError<P> {
     MiniscriptPsbt(MiniscriptPsbtError),
 }
 
-impl<P> fmt::Display for CreateTxError<P>
-where
-    P: fmt::Display,
-{
+impl fmt::Display for CreateTxError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             Self::Descriptor(e) => e.fmt(f),
             Self::Persist(e) => {
                 write!(
                     f,
-                    "failed to write wallet data to persistence backend: {}",
+                    "failed to load wallet data from or write wallet data to persistence backend: {}",
                     e
                 )
             }
@@ -214,38 +211,38 @@ where
     }
 }
 
-impl<P> From<descriptor::error::Error> for CreateTxError<P> {
+impl From<descriptor::error::Error> for CreateTxError {
     fn from(err: descriptor::error::Error) -> Self {
         CreateTxError::Descriptor(err)
     }
 }
 
-impl<P> From<PolicyError> for CreateTxError<P> {
+impl From<PolicyError> for CreateTxError {
     fn from(err: PolicyError) -> Self {
         CreateTxError::Policy(err)
     }
 }
 
-impl<P> From<MiniscriptPsbtError> for CreateTxError<P> {
+impl From<MiniscriptPsbtError> for CreateTxError {
     fn from(err: MiniscriptPsbtError) -> Self {
         CreateTxError::MiniscriptPsbt(err)
     }
 }
 
-impl<P> From<psbt::Error> for CreateTxError<P> {
+impl From<psbt::Error> for CreateTxError {
     fn from(err: psbt::Error) -> Self {
         CreateTxError::Psbt(err)
     }
 }
 
-impl<P> From<coin_selection::Error> for CreateTxError<P> {
+impl From<coin_selection::Error> for CreateTxError {
     fn from(err: coin_selection::Error) -> Self {
         CreateTxError::CoinSelection(err)
     }
 }
 
 #[cfg(feature = "std")]
-impl<P: core::fmt::Display + core::fmt::Debug> std::error::Error for CreateTxError<P> {}
+impl std::error::Error for CreateTxError {}
 
 #[derive(Debug)]
 /// Error returned from [`Wallet::build_fee_bump`]

crates/bdk/src/wallet/export.rs

@@ -53,9 +53,8 @@
 //! # Ok::<_, Box<dyn std::error::Error>>(())
 //! ```
 
-use core::str::FromStr;
-
 use alloc::string::{String, ToString};
+use core::str::FromStr;
 use serde::{Deserialize, Serialize};
 
 use miniscript::descriptor::{ShInner, WshInner};
@@ -110,8 +109,8 @@ impl FullyNodedExport {
     ///
     /// If the database is empty or `include_blockheight` is false, the `blockheight` field
     /// returned will be `0`.
-    pub fn export_wallet<D>(
-        wallet: &Wallet<D>,
+    pub fn export_wallet(
+        wallet: &Wallet,
         label: &str,
         include_blockheight: bool,
     ) -> Result<Self, &'static str> {
@@ -225,7 +224,7 @@ mod test {
         descriptor: &str,
         change_descriptor: Option<&str>,
         network: Network,
-    ) -> Wallet<()> {
+    ) -> Wallet {
         let mut wallet = Wallet::new_no_persist(descriptor, change_descriptor, network).unwrap();
         let transaction = Transaction {
             input: vec![],