miniscript: translate_pkk to take and return both pk and pkh

This adds the optional Pk to the translation methods, which allows
Descriptor with extended public keys to derive keys behind hashes.

Signed-off-by: Antoine Poinsot <darosior@protonmail.com>

src/descriptor/mod.rs

@@ -336,7 +336,7 @@ impl<Pk: MiniscriptKey> Descriptor<Pk> {
     ) -> Result<Descriptor<Q>, E>
     where
         Fpk: FnMut(&Pk) -> Result<Q, E>,
-        Fpkh: FnMut(&Pk::Hash) -> Result<Q::Hash, E>,
+        Fpkh: FnMut(&Option<Pk>, &Pk::Hash) -> Result<(Option<Q>, Q::Hash), E>,
         Q: MiniscriptKey,
     {
         match *self {
@@ -684,8 +684,11 @@ impl<Pk: MiniscriptKey + ToPublicKey> Descriptor<Pk> {
 }
 
 impl Descriptor<DescriptorPublicKey> {
-    /// Derives all wildcard keys in the descriptor using the supplied `child_number`
-    pub fn derive(&self, child_number: bip32::ChildNumber) -> Descriptor<DescriptorPublicKey> {
+    /// Derives all wildcard keys in the descriptor using the supplied `path`
+    pub fn derive(
+        &self,
+        child_number: bip32::ChildNumber,
+    ) -> Result<Descriptor<DescriptorPublicKey>, Error> {
         self.translate_pk(
             |pk| Result::Ok::<DescriptorPublicKey, ()>(pk.clone().derive(child_number)),
             |pk, _| match *pk {
@@ -700,7 +703,7 @@ impl Descriptor<DescriptorPublicKey> {
                 None => Err(()),
             },
         )
-        .expect("Translation fn can't fail.")
+        .map_err(|_| Error::BadDescriptor)
     }
 }
 
@@ -1522,8 +1525,9 @@ pk(xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHW
 pk(03f28773c2d975288bc7d1d205c3748651b075fbc6610e58cddeeddf8f19405aa8))";
         let policy: policy::concrete::Policy<DescriptorPublicKey> = descriptor_str.parse().unwrap();
         let descriptor = Descriptor::Sh(policy.compile().unwrap());
-        let derived_descriptor =
-            descriptor.derive(bip32::ChildNumber::from_normal_idx(42).unwrap());
+        let derived_descriptor = descriptor
+            .derive(bip32::ChildNumber::from_normal_idx(42).unwrap())
+            .expect("Deriving descriptor");
 
         let res_descriptor_str = "thresh(2,\
 pk([d34db33f/44'/0'/0']xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/42),\

src/miniscript/astelem.rs

@@ -70,15 +70,15 @@ impl<Pk: MiniscriptKey, Ctx: ScriptContext> Terminal<Pk, Ctx> {
     ) -> Result<Terminal<Q, Ctx>, Error>
     where
         FPk: FnMut(&Pk) -> Result<Q, Error>,
-        FPkh: FnMut(&Pk::Hash) -> Result<Q::Hash, Error>,
+        FPkh: FnMut(&Option<Pk>, &Pk::Hash) -> Result<(Option<Q>, Q::Hash), Error>,
         Q: MiniscriptKey,
     {
         let frag = match *self {
             Terminal::PkK(ref p) => Terminal::PkK(translatefpk(p)?),
-            Terminal::PkH(ref pk, ref pkh) => match pk {
-                Some(pk) => Terminal::PkH(Some(translatefpk(pk)?), translatefpkh(pkh)?),
-                None => Terminal::PkH(None, translatefpkh(pkh)?),
-            },
+            Terminal::PkH(ref pk, ref pkh) => {
+                let (pk, pkh) = translatefpkh(pk, pkh)?;
+                Terminal::PkH(pk, pkh)
+            }
             Terminal::After(n) => Terminal::After(n),
             Terminal::Older(n) => Terminal::Older(n),
             Terminal::Sha256(x) => Terminal::Sha256(x),

src/miniscript/mod.rs

@@ -219,7 +219,7 @@ impl<Pk: MiniscriptKey, Ctx: ScriptContext> Miniscript<Pk, Ctx> {
     ) -> Result<Miniscript<Q, Ctx>, FuncError>
     where
         FPk: FnMut(&Pk) -> Result<Q, FuncError>,
-        FPkh: FnMut(&Pk::Hash) -> Result<Q::Hash, FuncError>,
+        FPkh: FnMut(&Option<Pk>, &Pk::Hash) -> Result<(Option<Q>, Q::Hash), FuncError>,
         Q: MiniscriptKey,
     {
         let inner = self.node.translate_pk(translatefpk, translatefpkh)?;
@@ -373,7 +373,7 @@ mod tests {
         assert_eq!(roundtrip, script);
 
         let translated: Result<_, ()> =
-            script.translate_pk(&mut |k| Ok(k.clone()), &mut |h| Ok(h.clone()));
+            script.translate_pk(&mut |k| Ok(k.clone()), &mut |_, h| Ok((None, h.clone())));
         assert_eq!(translated, Ok(script));
     }