backend: make hash_length() specifically about commit IDs

The function is currently only about the length of commit IDs, so
let's clarify that. I'm going to add another function for the length
of change IDs next. I don't know if we're going to care about lengths
of other hashes in the future. We might even be able to remove the
current restriction that all commit IDs and all change IDs have the
same length.

examples/custom-backend/main.rs

@@ -92,8 +92,8 @@ impl Backend for JitBackend {
         "jit"
     }
 
-    fn hash_length(&self) -> usize {
-        self.inner.hash_length()
+    fn commit_id_length(&self) -> usize {
+        self.inner.commit_id_length()
     }
 
     fn git_repo(&self) -> Option<Repository> {

lib/src/backend.rs

@@ -383,7 +383,8 @@ pub trait Backend: Send + Sync + Debug {
     /// `.jj/repo/store/backend` when the repo is created.
     fn name(&self) -> &str;
 
-    fn hash_length(&self) -> usize;
+    /// The length of commit IDs in bytes.
+    fn commit_id_length(&self) -> usize;
 
     fn git_repo(&self) -> Option<git2::Repository>;
 

lib/src/git_backend.rs

@@ -187,7 +187,7 @@ impl Backend for GitBackend {
         "git"
     }
 
-    fn hash_length(&self) -> usize {
+    fn commit_id_length(&self) -> usize {
         HASH_LENGTH
     }
 

lib/src/index.rs

@@ -158,14 +158,14 @@ impl<'a> IndexRef<'a> {
 
 struct CommitGraphEntry<'a> {
     data: &'a [u8],
-    hash_length: usize,
+    commit_id_length: usize,
 }
 
 // TODO: Add pointers to ancestors further back, like a skip list. Clear the
 // lowest set bit to determine which generation number the pointers point to.
 impl CommitGraphEntry<'_> {
-    fn size(hash_length: usize) -> usize {
-        36 + hash_length
+    fn size(commit_id_length: usize) -> usize {
+        36 + commit_id_length
     }
 
     fn generation_number(&self) -> u32 {
@@ -195,18 +195,18 @@ impl CommitGraphEntry<'_> {
     }
 
     fn commit_id(&self) -> CommitId {
-        CommitId::from_bytes(&self.data[36..36 + self.hash_length])
+        CommitId::from_bytes(&self.data[36..36 + self.commit_id_length])
     }
 }
 
 struct CommitLookupEntry<'a> {
     data: &'a [u8],
-    hash_length: usize,
+    commit_id_length: usize,
 }
 
 impl CommitLookupEntry<'_> {
-    fn size(hash_length: usize) -> usize {
-        hash_length + 4
+    fn size(commit_id_length: usize) -> usize {
+        commit_id_length + 4
     }
 
     fn commit_id(&self) -> CommitId {
@@ -215,12 +215,12 @@ impl CommitLookupEntry<'_> {
 
     // might be better to add borrowed version of CommitId
     fn commit_id_bytes(&self) -> &[u8] {
-        &self.data[0..self.hash_length]
+        &self.data[0..self.commit_id_length]
     }
 
     fn pos(&self) -> IndexPosition {
         IndexPosition(
-            (&self.data[self.hash_length..self.hash_length + 4])
+            (&self.data[self.commit_id_length..self.commit_id_length + 4])
                 .read_u32::<LittleEndian>()
                 .unwrap(),
         )
@@ -255,7 +255,7 @@ pub struct ReadonlyIndex {
     parent_file: Option<Arc<ReadonlyIndex>>,
     num_parent_commits: u32,
     name: String,
-    hash_length: usize,
+    commit_id_length: usize,
     commit_graph_entry_size: usize,
     commit_lookup_entry_size: usize,
     // Number of commits not counting the parent file
@@ -373,17 +373,17 @@ struct MutableGraphEntry {
 pub struct MutableIndex {
     parent_file: Option<Arc<ReadonlyIndex>>,
     num_parent_commits: u32,
-    hash_length: usize,
+    commit_id_length: usize,
     graph: Vec<MutableGraphEntry>,
     lookup: BTreeMap<CommitId, IndexPosition>,
 }
 
 impl MutableIndex {
-    pub(crate) fn full(hash_length: usize) -> Self {
+    pub(crate) fn full(commit_id_length: usize) -> Self {
         Self {
             parent_file: None,
             num_parent_commits: 0,
-            hash_length,
+            commit_id_length,
             graph: vec![],
             lookup: BTreeMap::new(),
         }
@@ -391,11 +391,11 @@ impl MutableIndex {
 
     pub fn incremental(parent_file: Arc<ReadonlyIndex>) -> Self {
         let num_parent_commits = parent_file.num_parent_commits + parent_file.num_local_commits;
-        let hash_length = parent_file.hash_length;
+        let commit_id_length = parent_file.commit_id_length;
         Self {
             parent_file: Some(parent_file),
             num_parent_commits,
-            hash_length,
+            commit_id_length,
             graph: vec![],
             lookup: BTreeMap::new(),
         }
@@ -534,7 +534,7 @@ impl MutableIndex {
             assert_eq!(entry.change_id.as_bytes().len(), 16);
             buf.write_all(entry.change_id.as_bytes()).unwrap();
 
-            assert_eq!(entry.commit_id.as_bytes().len(), self.hash_length);
+            assert_eq!(entry.commit_id.as_bytes().len(), self.commit_id_length);
             buf.write_all(entry.commit_id.as_bytes()).unwrap();
         }
 
@@ -576,7 +576,7 @@ impl MutableIndex {
                     maybe_parent_file = parent_file.parent_file.clone();
                 }
                 None => {
-                    squashed = MutableIndex::full(self.hash_length);
+                    squashed = MutableIndex::full(self.commit_id_length);
                     break;
                 }
             }
@@ -598,7 +598,7 @@ impl MutableIndex {
             return Ok(self.parent_file.unwrap());
         }
 
-        let hash_length = self.hash_length;
+        let commit_id_length = self.commit_id_length;
 
         let buf = self.maybe_squash_with_ancestors().serialize();
         let mut hasher = Blake2b512::new();
@@ -612,14 +612,14 @@ impl MutableIndex {
         persist_content_addressed_temp_file(temp_file, index_file_path)?;
 
         let mut cursor = Cursor::new(&buf);
-        ReadonlyIndex::load_from(&mut cursor, dir, index_file_id_hex, hash_length).map_err(|err| {
-            match err {
+        ReadonlyIndex::load_from(&mut cursor, dir, index_file_id_hex, commit_id_length).map_err(
+            |err| match err {
                 IndexLoadError::IndexCorrupt(err) => {
                     panic!("Just-created index file is corrupt: {err}")
                 }
                 IndexLoadError::IoError(err) => err,
-            }
-        })
+            },
+        )
     }
 
     pub fn num_commits(&self) -> u32 {
@@ -1543,7 +1543,7 @@ impl ReadonlyIndex {
         file: &mut dyn Read,
         dir: PathBuf,
         name: String,
-        hash_length: usize,
+        commit_id_length: usize,
     ) -> Result<Arc<ReadonlyIndex>, IndexLoadError> {
         let parent_filename_len = file.read_u32::<LittleEndian>()?;
         let num_parent_commits;
@@ -1555,7 +1555,7 @@ impl ReadonlyIndex {
             let parent_file_path = dir.join(&parent_filename);
             let mut index_file = File::open(parent_file_path).unwrap();
             let parent_file =
-                ReadonlyIndex::load_from(&mut index_file, dir, parent_filename, hash_length)?;
+                ReadonlyIndex::load_from(&mut index_file, dir, parent_filename, commit_id_length)?;
             num_parent_commits = parent_file.num_parent_commits + parent_file.num_local_commits;
             maybe_parent_file = Some(parent_file);
         } else {
@@ -1566,9 +1566,9 @@ impl ReadonlyIndex {
         let num_parent_overflow_entries = file.read_u32::<LittleEndian>()?;
         let mut data = vec![];
         file.read_to_end(&mut data)?;
-        let commit_graph_entry_size = CommitGraphEntry::size(hash_length);
+        let commit_graph_entry_size = CommitGraphEntry::size(commit_id_length);
         let graph_size = (num_commits as usize) * commit_graph_entry_size;
-        let commit_lookup_entry_size = CommitLookupEntry::size(hash_length);
+        let commit_lookup_entry_size = CommitLookupEntry::size(commit_id_length);
         let lookup_size = (num_commits as usize) * commit_lookup_entry_size;
         let parent_overflow_size = (num_parent_overflow_entries as usize) * 4;
         let expected_size = graph_size + lookup_size + parent_overflow_size;
@@ -1582,7 +1582,7 @@ impl ReadonlyIndex {
             parent_file: maybe_parent_file,
             num_parent_commits,
             name,
-            hash_length,
+            commit_id_length,
             commit_graph_entry_size,
             commit_lookup_entry_size,
             num_local_commits: num_commits,
@@ -1662,7 +1662,7 @@ impl ReadonlyIndex {
         let offset = (local_pos as usize) * self.commit_graph_entry_size;
         CommitGraphEntry {
             data: &self.graph[offset..offset + self.commit_graph_entry_size],
-            hash_length: self.hash_length,
+            commit_id_length: self.commit_id_length,
         }
     }
 
@@ -1670,7 +1670,7 @@ impl ReadonlyIndex {
         let offset = (lookup_pos as usize) * self.commit_lookup_entry_size;
         CommitLookupEntry {
             data: &self.lookup[offset..offset + self.commit_lookup_entry_size],
-            hash_length: self.hash_length,
+            commit_id_length: self.commit_id_length,
         }
     }
 

lib/src/index_store.rs

@@ -54,7 +54,7 @@ impl IndexStore {
         let op_id_hex = op.id().hex();
         let op_id_file = self.dir.join("operations").join(op_id_hex);
         if op_id_file.exists() {
-            match self.load_index_at_operation(store.hash_length(), op.id()) {
+            match self.load_index_at_operation(store.commit_id_length(), op.id()) {
                 Err(IndexLoadError::IndexCorrupt(_)) => {
                     // If the index was corrupt (maybe it was written in a different format),
                     // we just reindex.
@@ -77,7 +77,7 @@ impl IndexStore {
 
     fn load_index_at_operation(
         &self,
-        hash_length: usize,
+        commit_id_length: usize,
         op_id: &OperationId,
     ) -> Result<Arc<ReadonlyIndex>, IndexLoadError> {
         let op_id_file = self.dir.join("operations").join(op_id.hex());
@@ -93,7 +93,7 @@ impl IndexStore {
             &mut index_file,
             self.dir.clone(),
             index_file_id_hex,
-            hash_length,
+            commit_id_length,
         )
     }
 
@@ -104,7 +104,7 @@ impl IndexStore {
     ) -> io::Result<Arc<ReadonlyIndex>> {
         let view = operation.view();
         let operations_dir = self.dir.join("operations");
-        let hash_length = store.hash_length();
+        let commit_id_length = store.commit_id_length();
         let mut new_heads = view.heads().clone();
         let mut parent_op_id: Option<OperationId> = None;
         for op in dag_walk::bfs(
@@ -127,11 +127,11 @@ impl IndexStore {
         match parent_op_id {
             None => {
                 maybe_parent_file = None;
-                data = MutableIndex::full(hash_length);
+                data = MutableIndex::full(commit_id_length);
             }
             Some(parent_op_id) => {
                 let parent_file = self
-                    .load_index_at_operation(hash_length, &parent_op_id)
+                    .load_index_at_operation(commit_id_length, &parent_op_id)
                     .unwrap();
                 maybe_parent_file = Some(parent_file.clone());
                 data = MutableIndex::incremental(parent_file)

lib/src/local_backend.rs

@@ -123,7 +123,7 @@ impl Backend for LocalBackend {
         "local"
     }
 
-    fn hash_length(&self) -> usize {
+    fn commit_id_length(&self) -> usize {
         64
     }
 

lib/src/revset.rs

@@ -86,7 +86,7 @@ fn resolve_full_commit_id(
     symbol: &str,
 ) -> Result<Option<Vec<CommitId>>, RevsetError> {
     if let Ok(binary_commit_id) = hex::decode(symbol) {
-        if repo.store().hash_length() != binary_commit_id.len() {
+        if repo.store().commit_id_length() != binary_commit_id.len() {
             return Ok(None);
         }
         let commit_id = CommitId::new(binary_commit_id);

lib/src/store.rs

@@ -43,8 +43,8 @@ impl Store {
         })
     }
 
-    pub fn hash_length(&self) -> usize {
-        self.backend.hash_length()
+    pub fn commit_id_length(&self) -> usize {
+        self.backend.commit_id_length()
     }
 
     pub fn git_repo(&self) -> Option<git2::Repository> {