Merge #299: Allow constructing Sh descriptors wrapping an existing Wsh/Wpkh

bd7c642 Allow constructing Sh descriptors wrapping an existing Wsh/Wpkh (Nadav Ivgi)

Pull request description:

  Useful if you already have an `W{s,pk}h` descriptor and wish to wrap it with P2SH.

  This used to be [possible](https://github.com/shesek/minsc/blob/33433462e84e3903a70a9aac6f47e591df094127/src/stdlib/miniscript.rs#L149-L153) before the new inner types for the Descriptor enum variants, which has private fields that cannot be initialized externally.

ACKs for top commit:
  apoelstra:
    ACK bd7c642
  sanket1729:
    ACK bd7c642

Tree-SHA512: c89f77d4cc8bcbda39f48361fc0693a7731ab2202f487dace44ab612fcdbd011476e6fbe79f1d429f10f9b1ea7e8ea1b164592e77e901030cec39f82dd764c02

Author: sanket1729

src/descriptor/mod.rs

@@ -277,6 +277,18 @@ impl<Pk: MiniscriptKey> Descriptor<Pk> {
         Ok(Descriptor::Bare(Bare::new(ms)?))
     }
 
+    // Wrap with sh
+
+    /// Create a new sh wrapper for the given wpkh descriptor
+    pub fn new_sh_with_wpkh(wpkh: Wpkh<Pk>) -> Self {
+        Descriptor::Sh(Sh::new_with_wpkh(wpkh))
+    }
+
+    /// Create a new sh wrapper for the given wsh descriptor
+    pub fn new_sh_with_wsh(wsh: Wsh<Pk>) -> Self {
+        Descriptor::Sh(Sh::new_with_wsh(wsh))
+    }
+
     // sorted multi
 
     /// Create a new sh sortedmulti descriptor with threshold `k`

src/descriptor/sh.rs

@@ -175,6 +175,13 @@ impl<Pk: MiniscriptKey> Sh<Pk> {
         })
     }
 
+    /// Create a new p2sh wrapper for the given wsh descriptor
+    pub fn new_with_wsh(wsh: Wsh<Pk>) -> Self {
+        Self {
+            inner: ShInner::Wsh(wsh),
+        }
+    }
+
     /// Create a new p2sh wrapped wsh sortedmulti descriptor from threshold
     /// `k` and Vec of `pks`
     pub fn new_wsh_sortedmulti(k: usize, pks: Vec<Pk>) -> Result<Self, Error> {
@@ -191,6 +198,13 @@ impl<Pk: MiniscriptKey> Sh<Pk> {
             inner: ShInner::Wpkh(Wpkh::new(pk)?),
         })
     }
+
+    /// Create a new p2sh wrapper for the given wpkh descriptor
+    pub fn new_with_wpkh(wpkh: Wpkh<Pk>) -> Self {
+        Self {
+            inner: ShInner::Wpkh(wpkh),
+        }
+    }
 }
 
 impl<Pk: MiniscriptKey + ToPublicKey> Sh<Pk> {