Merge #426: Rework translate API to allow associated types to be translated

8e5b09b Introduce Translator trait (sanket1729)
851120e Add impl_from_tree! (sanket1729)
c43129c Misc rustfmt change (sanket1729)

Pull request description:

  The Translate API currently does not support translating the hashes and timelocks. Ideally, we want to write an HTLC as `or( and( alice_key, older(timeout), and(bob_key, sha256(hash)))`.
  But it is impossible to use placeholders for `hash`, and `timelock`. It is only possible for keys.

  This is a significant API change, but I think it is for good. The diff is large, but reviewing `lib.rs` is the main diff, other diffs are just chasing compiler errors

ACKs for top commit:
  tcharding:
    ACK 8e5b09b
  apoelstra:
    ACK 8e5b09b

Tree-SHA512: 291ccbbb76a4768c83878728288db117ed2fc45608f911ac02d8e3ec0a2ef384c10e0e086a9debf76d324978f8a6f6812f737b276a86194b3d93a032c3bd6c7d

Author: sanket1729

examples/xpub_descriptors.rs

@@ -18,7 +18,7 @@ use std::str::FromStr;
 
 use miniscript::bitcoin::secp256k1::{Secp256k1, Verification};
 use miniscript::bitcoin::{Address, Network};
-use miniscript::{Descriptor, DescriptorPublicKey, TranslatePk2};
+use miniscript::{Descriptor, DescriptorPublicKey};
 
 const XPUB_1: &str = "xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB";
 const XPUB_2: &str = "xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH";
@@ -42,7 +42,7 @@ fn p2wsh<C: Verification>(secp: &Secp256k1<C>) -> Address {
 
     let address = Descriptor::<DescriptorPublicKey>::from_str(&s)
         .unwrap()
-        .translate_pk2(|xpk| xpk.derive_public_key(secp))
+        .derived_descriptor(&secp, 0) // dummy index value if it not a wildcard
         .unwrap()
         .address(Network::Bitcoin)
         .unwrap();

src/descriptor/bare.rs

@@ -19,7 +19,6 @@
 //!
 
 use core::fmt;
-use core::str::FromStr;
 
 use bitcoin::blockdata::script;
 use bitcoin::{Address, Network, Script};
@@ -32,7 +31,7 @@ use crate::prelude::*;
 use crate::util::{varint_len, witness_to_scriptsig};
 use crate::{
     BareCtx, Error, ForEach, ForEachKey, Miniscript, MiniscriptKey, Satisfier, ToPublicKey,
-    TranslatePk,
+    TranslatePk, Translator,
 };
 
 /// Create a Bare Descriptor. That is descriptor that is
@@ -145,35 +144,24 @@ impl<Pk: MiniscriptKey> Liftable<Pk> for Bare<Pk> {
     }
 }
 
-impl<Pk> FromTree for Bare<Pk>
-where
-    Pk: MiniscriptKey + FromStr,
-    Pk::Hash: FromStr,
-    <Pk as FromStr>::Err: ToString,
-    <<Pk as MiniscriptKey>::Hash as FromStr>::Err: ToString,
-{
+impl_from_tree!(
+    Bare<Pk>,
     fn from_tree(top: &expression::Tree) -> Result<Self, Error> {
         let sub = Miniscript::<Pk, BareCtx>::from_tree(top)?;
         BareCtx::top_level_checks(&sub)?;
         Bare::new(sub)
     }
-}
-
-impl<Pk> FromStr for Bare<Pk>
-where
-    Pk: MiniscriptKey + FromStr,
-    Pk::Hash: FromStr,
-    <Pk as FromStr>::Err: ToString,
-    <<Pk as MiniscriptKey>::Hash as FromStr>::Err: ToString,
-{
-    type Err = Error;
+);
 
+impl_from_str!(
+    Bare<Pk>,
+    type Err = Error;,
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         let desc_str = verify_checksum(s)?;
         let top = expression::Tree::from_str(desc_str)?;
         Self::from_tree(&top)
     }
-}
+);
 
 impl<Pk: MiniscriptKey> ForEachKey<Pk> for Bare<Pk> {
     fn for_each_key<'a, F: FnMut(ForEach<'a, Pk>) -> bool>(&'a self, pred: F) -> bool
@@ -192,14 +180,11 @@ where
 {
     type Output = Bare<Q>;
 
-    fn translate_pk<Fpk, Fpkh, E>(&self, mut fpk: Fpk, mut fpkh: Fpkh) -> Result<Self::Output, E>
+    fn translate_pk<T, E>(&self, t: &mut T) -> Result<Self::Output, E>
     where
-        Fpk: FnMut(&P) -> Result<Q, E>,
-        Fpkh: FnMut(&P::Hash) -> Result<Q::Hash, E>,
-        Q: MiniscriptKey,
+        T: Translator<P, Q, E>,
     {
-        Ok(Bare::new(self.ms.translate_pk(&mut fpk, &mut fpkh)?)
-            .expect("Translation cannot fail inside Bare"))
+        Ok(Bare::new(self.ms.translate_pk(t)?).expect("Translation cannot fail inside Bare"))
     }
 }
 
@@ -313,13 +298,8 @@ impl<Pk: MiniscriptKey> Liftable<Pk> for Pkh<Pk> {
     }
 }
 
-impl<Pk> FromTree for Pkh<Pk>
-where
-    Pk: MiniscriptKey + FromStr,
-    Pk::Hash: FromStr,
-    <Pk as FromStr>::Err: ToString,
-    <<Pk as MiniscriptKey>::Hash as FromStr>::Err: ToString,
-{
+impl_from_tree!(
+    Pkh<Pk>,
     fn from_tree(top: &expression::Tree) -> Result<Self, Error> {
         if top.name == "pkh" && top.args.len() == 1 {
             Ok(Pkh::new(expression::terminal(&top.args[0], |pk| {
@@ -333,23 +313,17 @@ where
             )))
         }
     }
-}
-
-impl<Pk> FromStr for Pkh<Pk>
-where
-    Pk: MiniscriptKey + FromStr,
-    Pk::Hash: FromStr,
-    <Pk as FromStr>::Err: ToString,
-    <<Pk as MiniscriptKey>::Hash as FromStr>::Err: ToString,
-{
-    type Err = Error;
+);
 
+impl_from_str!(
+    Pkh<Pk>,
+    type Err = Error;,
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         let desc_str = verify_checksum(s)?;
         let top = expression::Tree::from_str(desc_str)?;
         Self::from_tree(&top)
     }
-}
+);
 
 impl<Pk: MiniscriptKey> ForEachKey<Pk> for Pkh<Pk> {
     fn for_each_key<'a, F: FnMut(ForEach<'a, Pk>) -> bool>(&'a self, mut pred: F) -> bool
@@ -368,11 +342,10 @@ where
 {
     type Output = Pkh<Q>;
 
-    fn translate_pk<Fpk, Fpkh, E>(&self, mut fpk: Fpk, _fpkh: Fpkh) -> Result<Self::Output, E>
+    fn translate_pk<T, E>(&self, t: &mut T) -> Result<Self::Output, E>
     where
-        Fpk: FnMut(&P) -> Result<Q, E>,
-        Fpkh: FnMut(&P::Hash) -> Result<Q::Hash, E>,
+        T: Translator<P, Q, E>,
     {
-        Ok(Pkh::new(fpk(&self.pk)?))
+        Ok(Pkh::new(t.pk(&self.pk)?))
     }
 }

src/descriptor/key.rs

@@ -4,7 +4,7 @@ use core::str::FromStr;
 use std::error;
 
 use bitcoin::hashes::hex::FromHex;
-use bitcoin::hashes::{hash160, Hash, HashEngine};
+use bitcoin::hashes::{hash160, sha256, Hash, HashEngine};
 use bitcoin::secp256k1::{Secp256k1, Signing, Verification};
 use bitcoin::util::bip32;
 use bitcoin::{self, XOnlyPublicKey, XpubIdentifier};
@@ -737,6 +737,7 @@ impl<K: InnerXKey> DescriptorXKey<K> {
 impl MiniscriptKey for DescriptorPublicKey {
     // This allows us to be able to derive public keys even for PkH s
     type Hash = Self;
+    type Sha256 = bitcoin::hashes::sha256::Hash;
 
     fn is_uncompressed(&self) -> bool {
         match self {
@@ -802,6 +803,7 @@ impl fmt::Display for DerivedDescriptorKey {
 impl MiniscriptKey for DerivedDescriptorKey {
     // This allows us to be able to derive public keys even for PkH s
     type Hash = Self;
+    type Sha256 = bitcoin::hashes::sha256::Hash;
 
     fn is_uncompressed(&self) -> bool {
         self.key.is_uncompressed()
@@ -825,6 +827,10 @@ impl ToPublicKey for DerivedDescriptorKey {
     fn hash_to_hash160(hash: &Self) -> hash160::Hash {
         hash.to_public_key().to_pubkeyhash()
     }
+
+    fn to_sha256(hash: &sha256::Hash) -> sha256::Hash {
+        *hash
+    }
 }
 
 #[cfg(test)]