feat: add ObjectId::is_empty_tree() as sybling of ::is_empty_blob().

Author: Byron

gix-hash/src/kind.rs

@@ -57,14 +57,14 @@ impl Kind {
         [0u8; Kind::longest().len_in_bytes()]
     }
 
-    /// Returns the amount of ascii-characters needed to encode this has in hex.
+    /// Returns the amount of bytes needed to encode this instance as hexadecimal characters.
     #[inline]
     pub const fn len_in_hex(&self) -> usize {
         match self {
             Kind::Sha1 => 40,
         }
     }
-    /// Returns the amount of bytes taken up by the hash of the current kind.
+    /// Returns the amount of bytes taken up by the hash of this instance.
     #[inline]
     pub const fn len_in_bytes(&self) -> usize {
         match self {
@@ -73,7 +73,7 @@ impl Kind {
     }
 
     /// Returns the kind of hash that would fit the given `hex_len`, or `None` if there is no fitting hash.
-    /// Note that 0 as `hex_len` fits always yields Sha1.
+    /// Note that `0` as `hex_len` up to 40 always yields `Sha1`.
     #[inline]
     pub const fn from_hex_len(hex_len: usize) -> Option<Self> {
         Some(match hex_len {
@@ -98,15 +98,15 @@ impl Kind {
         }
     }
 
-    /// Create a null-id of our hash kind.
+    /// Create a shared null-id of our hash kind.
     #[inline]
     pub fn null_ref(&self) -> &'static oid {
         match self {
             Kind::Sha1 => oid::null_sha1(),
         }
     }
 
-    /// Create a null-id of our hash kind.
+    /// Create an owned null-id of our hash kind.
     #[inline]
     pub const fn null(&self) -> ObjectId {
         match self {

gix-hash/src/lib.rs

@@ -1,6 +1,6 @@
 //! This crate provides types for identifying git objects using a hash digest.
 //!
-//! These are provided in borrowed versions as well as owned ones.
+//! These are provided in [borrowed versions][oid] as well as an [owned one][ObjectId].
 //! ## Feature Flags
 #![cfg_attr(
     feature = "document-features",
@@ -19,8 +19,10 @@ pub use object_id::{decode, ObjectId};
 ///
 pub mod prefix;
 
-/// An partial owned hash possibly identifying an object uniquely,
-/// whose non-prefix bytes are zeroed.
+/// An partial, owned hash possibly identifying an object uniquely, whose non-prefix bytes are zeroed.
+///
+/// An example would `0000000000000000000000000000000032bd3242`, where `32bd3242` is the prefix,
+/// which would be able to match all hashes that *start with* `32bd3242`.
 #[derive(PartialEq, Eq, Hash, Ord, PartialOrd, Clone, Copy, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Prefix {
@@ -31,7 +33,7 @@ pub struct Prefix {
 /// The size of a SHA1 hash digest in bytes.
 const SIZE_OF_SHA1_DIGEST: usize = 20;
 
-/// Denotes the kind of function to produce a `Id`.
+/// Denotes the kind of function to produce a [`ObjectId`].
 #[derive(Default, PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum Kind {

gix-hash/src/object_id.rs

@@ -1,14 +1,13 @@
 use std::{
     borrow::Borrow,
     convert::TryInto,
-    fmt,
     hash::{Hash, Hasher},
     ops::Deref,
 };
 
 use crate::{borrowed::oid, Kind, SIZE_OF_SHA1_DIGEST};
 
-/// An owned hash identifying objects, most commonly Sha1
+/// An owned hash identifying objects, most commonly `Sha1`
 #[derive(PartialEq, Eq, Ord, PartialOrd, Clone, Copy)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum ObjectId {
@@ -77,11 +76,11 @@ pub mod decode {
 
 /// Access and conversion
 impl ObjectId {
-    /// Returns the kind of hash used in this `Id`.
+    /// Returns the kind of hash used in this instance.
     #[inline]
-    pub fn kind(&self) -> crate::Kind {
+    pub fn kind(&self) -> Kind {
         match self {
-            ObjectId::Sha1(_) => crate::Kind::Sha1,
+            ObjectId::Sha1(_) => Kind::Sha1,
         }
     }
     /// Return the raw byte slice representing this hash.
@@ -119,7 +118,15 @@ impl ObjectId {
         }
     }
 
-    /// Returns true if this hash consists of all null bytes.
+    /// Returns an instances whose bytes are all zero.
+    #[inline]
+    pub const fn null(kind: Kind) -> ObjectId {
+        match kind {
+            Kind::Sha1 => Self::null_sha1(),
+        }
+    }
+
+    /// Returns `true` if this hash consists of all null bytes.
     #[inline]
     pub fn is_null(&self) -> bool {
         match self {
@@ -133,12 +140,10 @@ impl ObjectId {
         self == &Self::empty_blob(self.kind())
     }
 
-    /// Returns an Digest representing a hash with whose memory is zeroed.
+    /// Returns `true` if this hash is equal to an empty tree.
     #[inline]
-    pub const fn null(kind: crate::Kind) -> ObjectId {
-        match kind {
-            crate::Kind::Sha1 => Self::null_sha1(),
-        }
+    pub fn is_empty_tree(&self) -> bool {
+        self == &Self::empty_tree(self.kind())
     }
 }
 
@@ -194,10 +199,10 @@ impl From<&[u8]> for ObjectId {
     }
 }
 
-impl From<&crate::oid> for ObjectId {
+impl From<&oid> for ObjectId {
     fn from(v: &oid) -> Self {
         match v.kind() {
-            crate::Kind::Sha1 => ObjectId::from_20_bytes(v.as_bytes()),
+            Kind::Sha1 => ObjectId::from_20_bytes(v.as_bytes()),
         }
     }
 }
@@ -210,25 +215,25 @@ impl Deref for ObjectId {
     }
 }
 
-impl AsRef<crate::oid> for ObjectId {
+impl AsRef<oid> for ObjectId {
     fn as_ref(&self) -> &oid {
         oid::from_bytes_unchecked(self.as_slice())
     }
 }
 
-impl Borrow<crate::oid> for ObjectId {
+impl Borrow<oid> for ObjectId {
     fn borrow(&self) -> &oid {
         self.as_ref()
     }
 }
 
-impl fmt::Display for ObjectId {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+impl std::fmt::Display for ObjectId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "{}", self.to_hex())
     }
 }
 
-impl PartialEq<&crate::oid> for ObjectId {
+impl PartialEq<&oid> for ObjectId {
     fn eq(&self, other: &&oid) -> bool {
         self.as_ref() == *other
     }

gix-hash/src/oid.rs

@@ -11,7 +11,7 @@ use crate::{ObjectId, SIZE_OF_SHA1_DIGEST};
 /// internal `bytes` slice length (a fat pointer, pointing to data and its length in bytes)
 /// to encode additional information. Before accessing or returning the bytes, a new adjusted
 /// slice will be constructed, while the high bits will be used to help resolving the
-/// hash `[`kind()`][oid::kind()]`.
+/// hash [`kind()`][oid::kind()].
 /// We expect to have quite a few bits available for such 'conflict resolution' as most hashes aren't longer
 /// than 64 bytes.
 #[derive(PartialEq, Eq, Ord, PartialOrd)]
@@ -102,13 +102,13 @@ impl oid {
 
 /// Access
 impl oid {
-    /// The kind of hash used for this Digest.
+    /// The kind of hash used for this instance.
     #[inline]
     pub fn kind(&self) -> crate::Kind {
         crate::Kind::from_len_in_bytes(self.bytes.len())
     }
 
-    /// The first byte of the hash, commonly used to partition a set of `Id`s.
+    /// The first byte of the hash, commonly used to partition a set of object ids.
     #[inline]
     pub fn first_byte(&self) -> u8 {
         self.bytes[0]