descriptor: Improve addr/address

Currently we have some duplicate code and unusual error wrapping.
Correctly handle the error returned when calculating an address. Use
`expect` when we have already checked for the failure. Improve the docs,
explaining what is called when and what its equivalent to.

Author: tcharding

src/descriptor/bare.rs

@@ -267,6 +267,7 @@ impl<Pk: MiniscriptKey + ToPublicKey> Pkh<Pk> {
     }
 
     /// Obtains the [`Address`] for this descriptor.
+    /// Called by [`DescriptorTrait::address`] for this descriptor.
     pub fn addr(&self, network: Network) -> Address {
         Address::p2pkh(&self.pk.to_public_key(), network)
     }

src/descriptor/segwitv0.rs

@@ -369,6 +369,7 @@ impl<Pk: MiniscriptKey + ToPublicKey> Wpkh<Pk> {
     }
 
     /// Obtains the [`Address`] for this descriptor.
+    /// Non failing version of [`DescriptorTrait::address`] for this descriptor.
     pub fn addr(&self, network: Network) -> Address {
         bitcoin::Address::p2wpkh(&self.pk.to_public_key(), network)
             .expect("Rust Miniscript types don't allow uncompressed pks in segwit descriptors")
@@ -466,7 +467,8 @@ impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Wpkh<Pk> {
     where
         Pk: ToPublicKey,
     {
-        Ok(self.addr(network))
+        let addr = Address::p2wpkh(&self.pk.to_public_key(), network)?;
+        Ok(addr)
     }
 
     fn script_pubkey(&self) -> Script

src/descriptor/sh.rs

@@ -220,20 +220,21 @@ impl<Pk: MiniscriptKey + ToPublicKey> Sh<Pk> {
     }
 
     /// Obtains the [`Address`] for this descriptor.
+    /// Non failing verion of [`DescriptorTrait::address`] for this descriptor.
     pub fn addr(&self, network: Network) -> Address {
+        self.address_fallible(network)
+            .expect("size checked in Miniscritp")
+    }
+
+    fn address_fallible(&self, network: Network) -> Result<Address, Error>
+    where
+        Pk: ToPublicKey,
+    {
         match self.inner {
-            ShInner::Wsh(ref wsh) => {
-                Address::p2sh(&wsh.spk(), network).expect("Size checked in Miniscript")
-            }
-            ShInner::Wpkh(ref wpkh) => {
-                Address::p2sh(&wpkh.spk(), network).expect("Size checked in Miniscript")
-            }
-            ShInner::SortedMulti(ref smv) => {
-                Address::p2sh(&smv.encode(), network).expect("Size checked in Miniscript")
-            }
-            ShInner::Ms(ref ms) => {
-                Address::p2sh(&ms.encode(), network).expect("Size checked in Miniscript")
-            }
+            ShInner::Wsh(ref wsh) => Ok(Address::p2sh(&wsh.spk(), network)?),
+            ShInner::Wpkh(ref wpkh) => Ok(Address::p2sh(&wpkh.spk(), network)?),
+            ShInner::SortedMulti(ref smv) => Ok(Address::p2sh(&smv.encode(), network)?),
+            ShInner::Ms(ref ms) => Ok(Address::p2sh(&ms.encode(), network)?),
         }
     }
 
@@ -278,12 +279,7 @@ impl<Pk: MiniscriptKey> DescriptorTrait<Pk> for Sh<Pk> {
     where
         Pk: ToPublicKey,
     {
-        match self.inner {
-            ShInner::Wsh(ref wsh) => Ok(Address::p2sh(&wsh.spk(), network)?),
-            ShInner::Wpkh(ref wpkh) => Ok(Address::p2sh(&wpkh.spk(), network)?),
-            ShInner::SortedMulti(ref smv) => Ok(Address::p2sh(&smv.encode(), network)?),
-            ShInner::Ms(ref ms) => Ok(Address::p2sh(&ms.encode(), network)?),
-        }
+        self.address_fallible(network)
     }
 
     fn script_pubkey(&self) -> Script

src/descriptor/tr.rs

@@ -286,6 +286,7 @@ impl<Pk: MiniscriptKey + ToPublicKey> Tr<Pk> {
     }
 
     /// Obtains the [`Address`] for this descriptor.
+    /// Called by [`DescriptorTrait::address`] for this descriptor.
     pub fn addr(&self, network: Network) -> Result<Address, Error> {
         let spend_info = self.spend_info();
         Ok(Address::p2tr_tweaked(spend_info.output_key(), network))