Remove unsigned_script_sig from Descriptor trait

The `unsigned_script_sig` method is only meaningfully implemented for Sh
descriptors, all the rest of the implementations just return
`Script::new()`. We can simplify the code by removing this method from
the `DescriptorTrait` altogether and just implementing it on
`Descriptor` and the Sh descriptor directly.

Author: tcharding

src/descriptor/bare.rs

@@ -138,13 +138,6 @@ where
 }
 
 impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Bare<Pk> {
-    fn unsigned_script_sig(&self) -> Script
-    where
-        Pk: ToPublicKey,
-    {
-        Script::new()
-    }
-
     fn get_satisfaction<S>(&self, satisfier: S) -> Result<(Vec<Vec<u8>>, Script), Error>
     where
         Pk: ToPublicKey,
@@ -319,13 +312,6 @@ where
 }
 
 impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Pkh<Pk> {
-    fn unsigned_script_sig(&self) -> Script
-    where
-        Pk: ToPublicKey,
-    {
-        Script::new()
-    }
-
     fn get_satisfaction<S>(&self, satisfier: S) -> Result<(Vec<Vec<u8>>, Script), Error>
     where
         Pk: ToPublicKey,

src/descriptor/mod.rs

@@ -79,18 +79,6 @@ pub type KeyMap = HashMap<DescriptorPublicKey, DescriptorSecretKey>;
 // because of traits cannot know underlying generic of Self.
 // Thus, we must implement additional trait for translate function
 pub trait DescriptorTrait<Pk: MiniscriptKey> {
-    /// Computes the scriptSig that will be in place for an unsigned
-    /// input spending an output with this descriptor. For pre-segwit
-    /// descriptors, which use the scriptSig for signatures, this
-    /// returns the empty script.
-    ///
-    /// This is used in Segwit transactions to produce an unsigned
-    /// transaction whose txid will not change during signing (since
-    /// only the witness data will change).
-    fn unsigned_script_sig(&self) -> Script
-    where
-        Pk: ToPublicKey;
-
     /// Returns satisfying non-malleable witness and scriptSig with minimum weight to spend an
     /// output controlled by the given descriptor if it possible to
     /// construct one using the satisfier S.
@@ -460,22 +448,21 @@ impl<Pk: MiniscriptKey + ToPublicKey> Descriptor<Pk> {
         }
     }
 
-    /// Computes the scriptSig that will be in place for an unsigned
-    /// input spending an output with this descriptor. For pre-segwit
-    /// descriptors, which use the scriptSig for signatures, this
-    /// returns the empty script.
+    /// Computes the scriptSig that will be in place for an unsigned input
+    /// spending an output with this descriptor. For pre-segwit descriptors,
+    /// which use the scriptSig for signatures, this returns the empty script.
     ///
-    /// This is used in Segwit transactions to produce an unsigned
-    /// transaction whose txid will not change during signing (since
-    /// only the witness data will change).
+    /// This is used in Segwit transactions to produce an unsigned transaction
+    /// whose txid will not change during signing (since only the witness data
+    /// will change).
     pub fn unsigned_script_sig(&self) -> Script {
         match *self {
-            Descriptor::Bare(ref bare) => bare.unsigned_script_sig(),
-            Descriptor::Pkh(ref pkh) => pkh.unsigned_script_sig(),
-            Descriptor::Wpkh(ref wpkh) => wpkh.unsigned_script_sig(),
-            Descriptor::Wsh(ref wsh) => wsh.unsigned_script_sig(),
+            Descriptor::Bare(_) => Script::new(),
+            Descriptor::Pkh(_) => Script::new(),
+            Descriptor::Wpkh(_) => Script::new(),
+            Descriptor::Wsh(_) => Script::new(),
             Descriptor::Sh(ref sh) => sh.unsigned_script_sig(),
-            Descriptor::Tr(ref tr) => tr.unsigned_script_sig(),
+            Descriptor::Tr(_) => Script::new(),
         }
     }
 

src/descriptor/segwitv0.rs

@@ -197,13 +197,6 @@ where
 }
 
 impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Wsh<Pk> {
-    fn unsigned_script_sig(&self) -> Script
-    where
-        Pk: ToPublicKey,
-    {
-        Script::new()
-    }
-
     fn get_satisfaction<S>(&self, satisfier: S) -> Result<(Vec<Vec<u8>>, Script), Error>
     where
         Pk: ToPublicKey,
@@ -436,13 +429,6 @@ where
 }
 
 impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Wpkh<Pk> {
-    fn unsigned_script_sig(&self) -> Script
-    where
-        Pk: ToPublicKey,
-    {
-        Script::new()
-    }
-
     fn get_satisfaction<S>(&self, satisfier: S) -> Result<(Vec<Vec<u8>>, Script), Error>
     where
         Pk: ToPublicKey,

src/descriptor/sh.rs

@@ -271,13 +271,15 @@ impl<Pk: MiniscriptKey + ToPublicKey> Sh<Pk> {
             ShInner::Ms(ref ms) => ms.encode(),
         }
     }
-}
 
-impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Sh<Pk> {
-    fn unsigned_script_sig(&self) -> Script
-    where
-        Pk: ToPublicKey,
-    {
+    /// Computes the scriptSig that will be in place for an unsigned input
+    /// spending an output with this descriptor. For pre-segwit descriptors,
+    /// which use the scriptSig for signatures, this returns the empty script.
+    ///
+    /// This is used in Segwit transactions to produce an unsigned transaction
+    /// whose txid will not change during signing (since only the witness data
+    /// will change).
+    pub fn unsigned_script_sig(&self) -> Script {
         match self.inner {
             ShInner::Wsh(ref wsh) => {
                 // wsh explicit must contain exactly 1 element
@@ -295,7 +297,9 @@ impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Sh<Pk> {
             ShInner::SortedMulti(..) | ShInner::Ms(..) => Script::new(),
         }
     }
+}
 
+impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Sh<Pk> {
     fn get_satisfaction<S>(&self, satisfier: S) -> Result<(Vec<Vec<u8>>, Script), Error>
     where
         Pk: ToPublicKey,

src/descriptor/tr.rs

@@ -559,13 +559,6 @@ impl<Pk: MiniscriptKey> Liftable<Pk> for Tr<Pk> {
 }
 
 impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Tr<Pk> {
-    fn unsigned_script_sig(&self) -> Script
-    where
-        Pk: ToPublicKey,
-    {
-        Script::new()
-    }
-
     fn get_satisfaction<S>(&self, satisfier: S) -> Result<(Vec<Vec<u8>>, Script), Error>
     where
         Pk: ToPublicKey,