fix!: hex-display of any object ID is now faster as oid::hex_to_buf() now returns &mut str.

This helps callers to avoid converting to UTF8 by hand.

Author: Byron

gix-hash/src/oid.rs

@@ -44,9 +44,9 @@ pub struct HexDisplay<'a> {
 impl std::fmt::Display for HexDisplay<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let mut hex = Kind::hex_buf();
-        let max_len = self.inner.hex_to_buf(hex.as_mut());
-        let hex = std::str::from_utf8(&hex[..self.hex_len.min(max_len)]).expect("ascii only in hex");
-        f.write_str(hex)
+        let hex = self.inner.hex_to_buf(hex.as_mut());
+        let max_len = hex.len();
+        f.write_str(&hex[..self.hex_len.min(max_len)])
     }
 }
 
@@ -152,22 +152,21 @@ impl oid {
 
 /// Sha1 specific methods
 impl oid {
-    /// Write ourselves to the `out` in hexadecimal notation, returning the amount of written bytes.
+    /// Write ourselves to the `out` in hexadecimal notation, returning the hex-string ready for display.
     ///
     /// **Panics** if the buffer isn't big enough to hold twice as many bytes as the current binary size.
     #[inline]
     #[must_use]
-    pub fn hex_to_buf(&self, buf: &mut [u8]) -> usize {
+    pub fn hex_to_buf<'a>(&self, buf: &'a mut [u8]) -> &'a mut str {
         let num_hex_bytes = self.bytes.len() * 2;
-        faster_hex::hex_encode(&self.bytes, &mut buf[..num_hex_bytes]).expect("to count correctly");
-        num_hex_bytes
+        faster_hex::hex_encode(&self.bytes, &mut buf[..num_hex_bytes]).expect("to count correctly")
     }
 
     /// Write ourselves to `out` in hexadecimal notation.
     #[inline]
     pub fn write_hex_to(&self, out: &mut dyn std::io::Write) -> std::io::Result<()> {
         let mut hex = Kind::hex_buf();
-        let hex_len = self.hex_to_buf(&mut hex);
+        let hex_len = self.hex_to_buf(&mut hex).len();
         out.write_all(&hex[..hex_len])
     }
 
@@ -210,10 +209,8 @@ impl<'a> From<&'a [u8; SIZE_OF_SHA1_DIGEST]> for &'a oid {
 
 impl std::fmt::Display for &oid {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        for b in self.as_bytes() {
-            write!(f, "{b:02x}")?;
-        }
-        Ok(())
+        let mut buf = Kind::hex_buf();
+        f.write_str(self.hex_to_buf(&mut buf))
     }
 }