feat: Add oid::is_empty_tree() and oid::is_empty_blob()`.

Author: Copilot

gix-hash/src/oid.rs

@@ -148,6 +148,22 @@ impl oid {
             Kind::Sha1 => &self.bytes == oid::null_sha1().as_bytes(),
         }
     }
+
+    /// Returns `true` if this hash is equal to an empty blob.
+    #[inline]
+    pub fn is_empty_blob(&self) -> bool {
+        match self.kind() {
+            Kind::Sha1 => &self.bytes == oid::empty_blob_sha1().as_bytes(),
+        }
+    }
+
+    /// Returns `true` if this hash is equal to an empty tree.
+    #[inline]
+    pub fn is_empty_tree(&self) -> bool {
+        match self.kind() {
+            Kind::Sha1 => &self.bytes == oid::empty_tree_sha1().as_bytes(),
+        }
+    }
 }
 
 /// Sha1 specific methods
@@ -175,6 +191,18 @@ impl oid {
     pub(crate) fn null_sha1() -> &'static Self {
         oid::from_bytes([0u8; SIZE_OF_SHA1_DIGEST].as_ref())
     }
+
+    /// Returns an oid representing the hash of an empty blob.
+    #[inline]
+    pub(crate) fn empty_blob_sha1() -> &'static Self {
+        oid::from_bytes(b"\xe6\x9d\xe2\x9b\xb2\xd1\xd6\x43\x4b\x8b\x29\xae\x77\x5a\xd8\xc2\xe4\x8c\x53\x91")
+    }
+
+    /// Returns an oid representing the hash of an empty tree.
+    #[inline]
+    pub(crate) fn empty_tree_sha1() -> &'static Self {
+        oid::from_bytes(b"\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04")
+    }
 }
 
 impl AsRef<oid> for &oid {

gix-hash/tests/hash/oid.rs

@@ -19,3 +19,44 @@ fn is_null() {
     assert!(gix_hash::Kind::Sha1.null().is_null());
     assert!(gix_hash::Kind::Sha1.null().as_ref().is_null());
 }
+
+#[test]
+fn is_empty_blob() {
+    // Test with ObjectId::empty_blob
+    let empty_blob = gix_hash::ObjectId::empty_blob(gix_hash::Kind::Sha1);
+    assert!(empty_blob.is_empty_blob());
+    assert!(empty_blob.as_ref().is_empty_blob());
+    
+    // Test that non-empty blob hash returns false
+    let non_empty = gix_hash::Kind::Sha1.null();
+    assert!(!non_empty.is_empty_blob());
+    assert!(!non_empty.as_ref().is_empty_blob());
+}
+
+#[test]
+fn is_empty_tree() {
+    // Test with ObjectId::empty_tree
+    let empty_tree = gix_hash::ObjectId::empty_tree(gix_hash::Kind::Sha1);
+    assert!(empty_tree.is_empty_tree());
+    assert!(empty_tree.as_ref().is_empty_tree());
+    
+    // Test that non-empty tree hash returns false
+    let non_empty = gix_hash::Kind::Sha1.null();
+    assert!(!non_empty.is_empty_tree());
+    assert!(!non_empty.as_ref().is_empty_tree());
+}
+
+#[test]
+fn oid_methods_are_consistent_with_objectid() {
+    // Verify that the oid methods return the same results as ObjectId methods
+    let empty_blob = gix_hash::ObjectId::empty_blob(gix_hash::Kind::Sha1);
+    let empty_tree = gix_hash::ObjectId::empty_tree(gix_hash::Kind::Sha1);
+    
+    // Check that ObjectId and oid versions give same results
+    assert_eq!(empty_blob.is_empty_blob(), empty_blob.as_ref().is_empty_blob());
+    assert_eq!(empty_tree.is_empty_tree(), empty_tree.as_ref().is_empty_tree());
+    
+    // Check cross-validation (empty blob is not empty tree and vice versa)
+    assert!(!empty_blob.as_ref().is_empty_tree());
+    assert!(!empty_tree.as_ref().is_empty_blob());
+}