feat: add Prefix::from_hex_nonempty() to allow creating short prefixes.

This can be useful in certain situations where the set of candidate object ids
is very small.

Author: Byron

Cargo.lock

@@ -93,12 +93,23 @@ impl Prefix {
     }
 
     /// Create an instance from the given hexadecimal prefix `value`, e.g. `35e77c16` would yield a `Prefix` with `hex_len()` = 8.
+    /// Note that the minimum hex length is `4` - use [`Self::from_hex_nonempty()`].
     pub fn from_hex(value: &str) -> Result<Self, from_hex::Error> {
         let hex_len = value.len();
+        if hex_len < Self::MIN_HEX_LEN {
+            return Err(from_hex::Error::TooShort { hex_len });
+        }
+        Self::from_hex_nonempty(value)
+    }
+
+    /// Create an instance from the given hexadecimal prefix `value`, e.g. `35e` would yield a `Prefix` with `hex_len()` = 3.
+    /// Note that this function supports all non-empty hex input - for a more typical implementation, use [`Self::from_hex()`].
+    pub fn from_hex_nonempty(value: &str) -> Result<Self, from_hex::Error> {
+        let hex_len = value.len();
 
         if hex_len > crate::Kind::longest().len_in_hex() {
             return Err(from_hex::Error::TooLong { hex_len });
-        } else if hex_len < Self::MIN_HEX_LEN {
+        } else if hex_len == 0 {
             return Err(from_hex::Error::TooShort { hex_len });
         }
 

gix-hash/src/prefix.rs

@@ -80,7 +80,7 @@ mod try_from {
     use crate::hex_to_id;
 
     #[test]
-    fn id_8_chars() {
+    fn id_6_chars() {
         let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";
         let input = "abcdef";
 
@@ -90,7 +90,7 @@ mod try_from {
     }
 
     #[test]
-    fn id_9_chars() {
+    fn id_7_chars() {
         let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";
         let input = "abcdefa";
 
@@ -107,7 +107,7 @@ mod try_from {
     }
 
     #[test]
-    fn id_to_long() {
+    fn id_too_long() {
         let input = "abcdefabcdefabcdefabcdefabcdefabcdefabcd123123123123123123";
         let expected = Error::TooLong { hex_len: 58 };
         let actual = Prefix::try_from(input).unwrap_err();
@@ -122,3 +122,59 @@ mod try_from {
         assert_eq!(actual, expected);
     }
 }
+
+mod from_hex_nonempty {
+    use std::cmp::Ordering;
+
+    use gix_hash::{prefix::from_hex::Error, Prefix};
+
+    use crate::hex_to_id;
+
+    #[test]
+    fn id_6_chars() {
+        let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";
+        let input = "abcdef";
+
+        let expected = hex_to_id(oid_hex);
+        let actual = Prefix::from_hex_nonempty(input).expect("No errors");
+        assert_eq!(actual.cmp_oid(&expected), Ordering::Equal);
+    }
+
+    #[test]
+    fn id_7_chars() {
+        let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";
+        let input = "abcdefa";
+
+        let expected = hex_to_id(oid_hex);
+        let actual = Prefix::from_hex_nonempty(input).expect("No errors");
+        assert_eq!(actual.cmp_oid(&expected), Ordering::Equal);
+    }
+
+    #[test]
+    fn id_2_chars_and_less() {
+        let oid_hex = "abcdefabcdefabcdefabcdefabcdefabcdefabcd";
+
+        let oid = hex_to_id(oid_hex);
+        let actual = Prefix::from_hex_nonempty("ab").expect("no errors");
+        assert_eq!(actual.cmp_oid(&oid), Ordering::Equal);
+
+        let actual = Prefix::from_hex_nonempty("a").expect("no errors");
+        assert_eq!(actual.cmp_oid(&oid), Ordering::Equal);
+    }
+
+    #[test]
+    fn id_empty() {
+        let input = "";
+        let expected = Error::TooShort { hex_len: 0 };
+        let actual = Prefix::from_hex_nonempty(input).unwrap_err();
+        assert_eq!(actual, expected);
+    }
+
+    #[test]
+    fn id_too_long() {
+        let input = "abcdefabcdefabcdefabcdefabcdefabcdefabcd123123123123123123";
+        let expected = Error::TooLong { hex_len: 58 };
+        let actual = Prefix::from_hex_nonempty(input).unwrap_err();
+        assert_eq!(actual, expected);
+    }
+}