Implement write_descriptor macro

Currently we have a bunch of places in the code where we create a
checksum formatter wrapper then write a descriptor to it then write the
checksum. This can all be wrapped up in a macro, has to be a macro
because the number of args is variable.

This reduces the line count with no real loss of clarity
`write_descriptor!` is pretty self explanatory.

src/descriptor/bare.rs

@@ -12,8 +12,8 @@ use core::fmt;
 use bitcoin::script::{self, PushBytes};
 use bitcoin::{Address, Network, ScriptBuf};
 
-use super::checksum::{self, verify_checksum};
-use crate::descriptor::DefiniteDescriptorKey;
+use super::checksum::verify_checksum;
+use crate::descriptor::{write_descriptor, DefiniteDescriptorKey};
 use crate::expression::{self, FromTree};
 use crate::miniscript::context::{ScriptContext, ScriptContextError};
 use crate::miniscript::satisfy::{Placeholder, Satisfaction, Witness};
@@ -156,12 +156,7 @@ impl<Pk: MiniscriptKey> fmt::Debug for Bare<Pk> {
 }
 
 impl<Pk: MiniscriptKey> fmt::Display for Bare<Pk> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        use fmt::Write;
-        let mut wrapped_f = checksum::Formatter::new(f);
-        write!(wrapped_f, "{}", self.ms)?;
-        wrapped_f.write_checksum_if_not_alt()
-    }
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write_descriptor!(f, "{}", self.ms) }
 }
 
 impl<Pk: MiniscriptKey> Liftable<Pk> for Bare<Pk> {
@@ -354,10 +349,7 @@ impl<Pk: MiniscriptKey> fmt::Debug for Pkh<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Pkh<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        use fmt::Write;
-        let mut wrapped_f = checksum::Formatter::new(f);
-        write!(wrapped_f, "pkh({})", self.pk)?;
-        wrapped_f.write_checksum_if_not_alt()
+        write_descriptor!(f, "pkh({})", self.pk)
     }
 }
 

src/descriptor/mod.rs

@@ -978,6 +978,21 @@ impl<Pk: MiniscriptKey> fmt::Display for Descriptor<Pk> {
 
 serde_string_impl_pk!(Descriptor, "a script descriptor");
 
+macro_rules! write_descriptor {
+    ($fmt:expr, $s:literal $(, $args:expr)*) => {
+        {
+            use fmt::Write as _;
+
+            let mut wrapped_f = $crate::descriptor::checksum::Formatter::new($fmt);
+            write!(wrapped_f, $s $(, $args)*)?;
+            wrapped_f.write_checksum_if_not_alt()?;
+
+            fmt::Result::Ok(())
+        }
+    }
+}
+pub(crate) use write_descriptor;
+
 #[cfg(test)]
 mod tests {
     use core::convert::TryFrom;

src/descriptor/segwitv0.rs

@@ -9,9 +9,9 @@ use core::fmt;
 
 use bitcoin::{Address, Network, ScriptBuf};
 
-use super::checksum::{self, verify_checksum};
+use super::checksum::verify_checksum;
 use super::SortedMultiVec;
-use crate::descriptor::DefiniteDescriptorKey;
+use crate::descriptor::{write_descriptor, DefiniteDescriptorKey};
 use crate::expression::{self, FromTree};
 use crate::miniscript::context::{ScriptContext, ScriptContextError};
 use crate::miniscript::satisfy::{Placeholder, Satisfaction, Witness};
@@ -260,13 +260,10 @@ impl<Pk: MiniscriptKey> fmt::Debug for Wsh<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Wsh<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        use fmt::Write;
-        let mut wrapped_f = checksum::Formatter::new(f);
         match self.inner {
-            WshInner::SortedMulti(ref smv) => write!(wrapped_f, "wsh({})", smv)?,
-            WshInner::Ms(ref ms) => write!(wrapped_f, "wsh({})", ms)?,
+            WshInner::SortedMulti(ref smv) => write_descriptor!(f, "wsh({})", smv),
+            WshInner::Ms(ref ms) => write_descriptor!(f, "wsh({})", ms),
         }
-        wrapped_f.write_checksum_if_not_alt()
     }
 }
 
@@ -461,10 +458,7 @@ impl<Pk: MiniscriptKey> fmt::Debug for Wpkh<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Wpkh<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        use fmt::Write;
-        let mut wrapped_f = checksum::Formatter::new(f);
-        write!(wrapped_f, "wpkh({})", self.pk)?;
-        wrapped_f.write_checksum_if_not_alt()
+        write_descriptor!(f, "wpkh({})", self.pk)
     }
 }
 

src/descriptor/sh.rs

@@ -13,9 +13,9 @@ use core::fmt;
 use bitcoin::script::PushBytes;
 use bitcoin::{script, Address, Network, ScriptBuf};
 
-use super::checksum::{self, verify_checksum};
+use super::checksum::verify_checksum;
 use super::{SortedMultiVec, Wpkh, Wsh};
-use crate::descriptor::DefiniteDescriptorKey;
+use crate::descriptor::{write_descriptor, DefiniteDescriptorKey};
 use crate::expression::{self, FromTree};
 use crate::miniscript::context::ScriptContext;
 use crate::miniscript::satisfy::{Placeholder, Satisfaction};
@@ -72,15 +72,12 @@ impl<Pk: MiniscriptKey> fmt::Debug for Sh<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Sh<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        use fmt::Write;
-        let mut wrapped_f = checksum::Formatter::new(f);
         match self.inner {
-            ShInner::Wsh(ref wsh) => write!(wrapped_f, "sh({:#})", wsh)?,
-            ShInner::Wpkh(ref pk) => write!(wrapped_f, "sh({:#})", pk)?,
-            ShInner::SortedMulti(ref smv) => write!(wrapped_f, "sh({})", smv)?,
-            ShInner::Ms(ref ms) => write!(wrapped_f, "sh({})", ms)?,
+            ShInner::Wsh(ref wsh) => write_descriptor!(f, "sh({:#})", wsh),
+            ShInner::Wpkh(ref pk) => write_descriptor!(f, "sh({:#})", pk),
+            ShInner::SortedMulti(ref smv) => write_descriptor!(f, "sh({})", smv),
+            ShInner::Ms(ref ms) => write_descriptor!(f, "sh({})", ms),
         }
-        wrapped_f.write_checksum_if_not_alt()
     }
 }