Merge rust-bitcoin#4620: Add alternate print format to DerivationPath using 'h' suffix

4284dee DerivationPath: support 'h' in Display output for hardened components (vicjuma)

Pull request description:

  DerivationPath now supports a display format using both 'h' a single quote (') to indicate hardened components.

  This aligns it with its ChildNumber's output style.

  Resolves: rust-bitcoin#4618

ACKs for top commit:
  apoelstra:
    ACK 4284dee; successfully ran local tests
  tcharding:
    ACK 4284dee

Tree-SHA512: 24e053c22ec94b851935debbab83d15ad9f41ccfca0a7c34a061450989b176295512e8ffb187b2a54c6c6926f82ec7e4a4186ccdba2ec2616a6e0603d90d2a9b

Author: apoelstra

bitcoin/src/bip32.rs

@@ -482,11 +482,19 @@ impl fmt::Display for DerivationPath {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let mut iter = self.0.iter();
         if let Some(first_element) = iter.next() {
-            write!(f, "{}", first_element)?;
+            if f.alternate() {
+                write!(f, "{:#}", first_element)?;
+            } else {
+                write!(f, "{}", first_element)?;
+            }
         }
         for cn in iter {
             f.write_str("/")?;
-            write!(f, "{}", cn)?;
+            if f.alternate() {
+                write!(f, "{:#}", cn)?;
+            } else {
+                write!(f, "{}", cn)?;
+            }
         }
         Ok(())
     }
@@ -1108,6 +1116,13 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_derivation_path_display() {
+        let path = DerivationPath::from_str("m/84'/0'/0'/0/0").unwrap();
+        assert_eq!(format!("{}", path), "84'/0'/0'/0/0");
+        assert_eq!(format!("{:#}", path), "84h/0h/0h/0/0");
+    }
+
     #[test]
     fn parse_derivation_path_out_of_range() {
         let invalid_path = "2147483648";