Merge #91: Avoid allocating a string in Display implementation

2684570 fix Display impl for ct desc (Riccardo Casatta)
589e67c fix Display impl for dynafed pegin (Riccardo Casatta)
9a93134 fix Display impl for legacy pegin (Riccardo Casatta)

Pull request description:

  This applies the changes in b11c818 to other Display implementations.

ACKs for top commit:
  apoelstra:
    ACK 2684570 successfully ran local tests

Tree-SHA512: 516c0592ff827ae181dc735562be3723a6fac9ee323dd9907a35d8c387c0495ef03993ff601fdf3ad82c6073ec1c809a5719a1a2ba69e2923cb37ace24580b3c

Author: apoelstra

src/confidential/mod.rs

@@ -26,7 +26,7 @@ use std::fmt;
 use bitcoin::bip32;
 use elements::secp256k1_zkp;
 
-use crate::descriptor::checksum::{desc_checksum, verify_checksum};
+use crate::descriptor::checksum::{self, verify_checksum};
 use crate::descriptor::{
     ConversionError, DefiniteDescriptorKey, DescriptorSecretKey, DescriptorPublicKey,
     DescriptorXKey, Wildcard
@@ -189,9 +189,10 @@ impl<Pk: MiniscriptKey + ToPublicKey, T: Extension + ParseableExt> Descriptor<Pk
 
 impl<Pk: MiniscriptKey, T: Extension> fmt::Display for Descriptor<Pk, T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let desc_str = format!("ct({},{:#})", self.key, self.descriptor);
-        let checksum = desc_checksum(&desc_str).map_err(|_| fmt::Error)?;
-        write!(f, "{}#{}", desc_str, checksum)
+        use fmt::Write;
+        let mut wrapped_f = checksum::Formatter::new(f);
+        write!(wrapped_f, "ct({},{:#})", self.key, self.descriptor)?;
+        wrapped_f.write_checksum_if_not_alt()
     }
 }
 

src/descriptor/pegin/dynafed_pegin.rs

@@ -27,7 +27,7 @@ use bitcoin::blockdata::script::{self, PushBytes};
 use bitcoin::{self, ScriptBuf as BtcScript};
 use elements::secp256k1_zkp;
 
-use crate::descriptor::checksum::{desc_checksum, verify_checksum};
+use crate::descriptor::checksum::{self, verify_checksum};
 use crate::expression::{self, FromTree};
 use crate::extensions::{CovExtArgs, CovenantExt};
 use crate::policy::{semantic, Liftable};
@@ -69,9 +69,10 @@ impl<Pk: MiniscriptKey> fmt::Debug for Pegin<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for Pegin<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let desc = format!("pegin({},{})", self.fed_desc, self.elem_desc);
-        let checksum = desc_checksum(&desc).map_err(|_| fmt::Error)?;
-        write!(f, "{}#{}", &desc, &checksum)
+        use fmt::Write;
+        let mut wrapped_f = checksum::Formatter::new(f);
+        write!(wrapped_f, "pegin({},{})", self.fed_desc, self.elem_desc)?;
+        wrapped_f.write_checksum_if_not_alt()
     }
 }
 

src/descriptor/pegin/legacy_pegin.rs

@@ -34,7 +34,7 @@ use bitcoin::{self, hashes, ScriptBuf as BtcScript};
 use bitcoin_miniscript::TranslatePk as BtcTranslatePk;
 use elements::secp256k1_zkp;
 
-use crate::descriptor::checksum::{desc_checksum, verify_checksum};
+use crate::descriptor::checksum::{self, verify_checksum};
 use crate::expression::{self, FromTree};
 use crate::extensions::{CovExtArgs, CovenantExt};
 use crate::policy::{semantic, Liftable};
@@ -326,9 +326,10 @@ impl<Pk: MiniscriptKey> fmt::Debug for LegacyPegin<Pk> {
 
 impl<Pk: MiniscriptKey> fmt::Display for LegacyPegin<Pk> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let desc = format!("legacy_pegin({},{})", self.ms, self.desc);
-        let checksum = desc_checksum(&desc).map_err(|_| fmt::Error)?;
-        write!(f, "{}#{}", &desc, &checksum)
+        use fmt::Write;
+        let mut wrapped_f = checksum::Formatter::new(f);
+        write!(wrapped_f, "legacy_pegin({},{})", self.ms, self.desc)?;
+        wrapped_f.write_checksum_if_not_alt()
     }
 }