index: rename ReadonlyIndexImpl to ReadonlyIndexSegment

I'm going to split the internal Segment types and the public Index types
in order to clarify the layering concept. The public Index types will be
wrappers like DefaultReadonlyIndex.

Strictly speaking, ReadonlyIndexImpl is a segment + parent pointer pair,
but I think calling it a segment is pretty okay. It could be called a
ReadonlyIndexFile, but "File" can't apply to the mutable part.

lib/src/default_index_store.rs

@@ -88,13 +88,13 @@ impl DefaultIndexStore {
         commit_id_length: usize,
         change_id_length: usize,
         op_id: &OperationId,
-    ) -> Result<Arc<ReadonlyIndexImpl>, IndexLoadError> {
+    ) -> Result<Arc<ReadonlyIndexSegment>, IndexLoadError> {
         let op_id_file = self.dir.join("operations").join(op_id.hex());
         let buf = fs::read(op_id_file).unwrap();
         let index_file_id_hex = String::from_utf8(buf).unwrap();
         let index_file_path = self.dir.join(&index_file_id_hex);
         let mut index_file = File::open(index_file_path).unwrap();
-        ReadonlyIndexImpl::load_from(
+        ReadonlyIndexSegment::load_from(
             &mut index_file,
             self.dir.to_owned(),
             index_file_id_hex,
@@ -108,7 +108,7 @@ impl DefaultIndexStore {
         &self,
         store: &Arc<Store>,
         operation: &Operation,
-    ) -> Result<Arc<ReadonlyIndexImpl>, DefaultIndexStoreError> {
+    ) -> Result<Arc<ReadonlyIndexSegment>, DefaultIndexStoreError> {
         let view = operation.view()?;
         let operations_dir = self.dir.join("operations");
         let commit_id_length = store.commit_id_length();
@@ -192,7 +192,7 @@ impl DefaultIndexStore {
     /// Records a link from the given operation to the this index version.
     fn associate_file_with_operation(
         &self,
-        index: &ReadonlyIndexImpl,
+        index: &ReadonlyIndexSegment,
         op_id: &OperationId,
     ) -> io::Result<()> {
         let mut temp_file = NamedTempFile::new_in(&self.dir)?;
@@ -218,7 +218,7 @@ impl IndexStore for DefaultIndexStore {
     fn get_index_at_op(&self, op: &Operation, store: &Arc<Store>) -> Box<dyn ReadonlyIndex> {
         let op_id_hex = op.id().hex();
         let op_id_file = self.dir.join("operations").join(op_id_hex);
-        let index_impl = if op_id_file.exists() {
+        let index_segment = if op_id_file.exists() {
             match self.load_index_at_operation(
                 store.commit_id_length(),
                 store.change_id_length(),
@@ -238,7 +238,7 @@ impl IndexStore for DefaultIndexStore {
         } else {
             self.index_at_operation(store, op).unwrap()
         };
-        Box::new(DefaultReadonlyIndex(index_impl))
+        Box::new(DefaultReadonlyIndex(index_segment))
     }
 
     fn write_index(
@@ -250,16 +250,16 @@ impl IndexStore for DefaultIndexStore {
             .into_any()
             .downcast::<MutableIndexImpl>()
             .expect("index to merge in must be a MutableIndexImpl");
-        let index = index.save_in(self.dir.clone()).map_err(|err| {
+        let index_segment = index.save_in(self.dir.clone()).map_err(|err| {
             IndexWriteError::Other(format!("Failed to write commit index file: {err}"))
         })?;
-        self.associate_file_with_operation(&index, op_id)
+        self.associate_file_with_operation(&index_segment, op_id)
             .map_err(|err| {
                 IndexWriteError::Other(format!(
                     "Failed to associate commit index file with a operation {op_id:?}: {err}"
                 ))
             })?;
-        Ok(Box::new(DefaultReadonlyIndex(index)))
+        Ok(Box::new(DefaultReadonlyIndex(index_segment)))
     }
 }
 
@@ -370,8 +370,8 @@ pub enum IndexLoadError {
 // TODO: replace the table by a trie so we don't have to repeat the full commit
 //       ids
 // TODO: add a fanout table like git's commit graph has?
-struct ReadonlyIndexImpl {
-    parent_file: Option<Arc<ReadonlyIndexImpl>>,
+struct ReadonlyIndexSegment {
+    parent_file: Option<Arc<ReadonlyIndexSegment>>,
     num_parent_commits: u32,
     name: String,
     commit_id_length: usize,
@@ -387,7 +387,7 @@ struct ReadonlyIndexImpl {
 
 /// Commit index backend which stores data on local disk.
 #[derive(Debug)]
-pub struct DefaultReadonlyIndex(Arc<ReadonlyIndexImpl>);
+pub struct DefaultReadonlyIndex(Arc<ReadonlyIndexSegment>);
 
 impl ReadonlyIndex for DefaultReadonlyIndex {
     fn as_any(&self) -> &dyn Any {
@@ -403,9 +403,9 @@ impl ReadonlyIndex for DefaultReadonlyIndex {
     }
 }
 
-impl Debug for ReadonlyIndexImpl {
+impl Debug for ReadonlyIndexSegment {
     fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), std::fmt::Error> {
-        f.debug_struct("ReadonlyIndex")
+        f.debug_struct("ReadonlyIndexSegment")
             .field("name", &self.name)
             .field("parent_file", &self.parent_file)
             .finish()
@@ -427,7 +427,7 @@ struct MutableGraphEntry {
 }
 
 pub struct MutableIndexImpl {
-    parent_file: Option<Arc<ReadonlyIndexImpl>>,
+    parent_file: Option<Arc<ReadonlyIndexSegment>>,
     num_parent_commits: u32,
     commit_id_length: usize,
     change_id_length: usize,
@@ -447,7 +447,7 @@ impl MutableIndexImpl {
         }
     }
 
-    fn incremental(parent_file: Arc<ReadonlyIndexImpl>) -> Self {
+    fn incremental(parent_file: Arc<ReadonlyIndexSegment>) -> Self {
         let num_parent_commits = parent_file.num_parent_commits + parent_file.num_local_commits;
         let commit_id_length = parent_file.commit_id_length;
         let change_id_length = parent_file.change_id_length;
@@ -609,7 +609,7 @@ impl MutableIndexImpl {
         squashed
     }
 
-    fn save_in(self, dir: PathBuf) -> io::Result<Arc<ReadonlyIndexImpl>> {
+    fn save_in(self, dir: PathBuf) -> io::Result<Arc<ReadonlyIndexSegment>> {
         if self.segment_num_commits() == 0 && self.parent_file.is_some() {
             return Ok(self.parent_file.unwrap());
         }
@@ -628,7 +628,7 @@ impl MutableIndexImpl {
         file.write_all(&buf)?;
         persist_content_addressed_temp_file(temp_file, index_file_path)?;
 
-        ReadonlyIndexImpl::load_from(
+        ReadonlyIndexSegment::load_from(
             &mut buf.as_slice(),
             dir,
             index_file_id_hex,
@@ -747,7 +747,7 @@ trait IndexSegment: Send + Sync {
 
     fn segment_num_commits(&self) -> u32;
 
-    fn segment_parent_file(&self) -> Option<&Arc<ReadonlyIndexImpl>>;
+    fn segment_parent_file(&self) -> Option<&Arc<ReadonlyIndexSegment>>;
 
     fn segment_name(&self) -> Option<String>;
 
@@ -779,7 +779,7 @@ trait IndexSegment: Send + Sync {
 pub struct CompositeIndex<'a>(&'a dyn IndexSegment);
 
 impl<'a> CompositeIndex<'a> {
-    fn ancestor_files_without_local(&self) -> impl Iterator<Item = &'a Arc<ReadonlyIndexImpl>> {
+    fn ancestor_files_without_local(&self) -> impl Iterator<Item = &'a Arc<ReadonlyIndexSegment>> {
         let parent_file = self.0.segment_parent_file();
         iter::successors(parent_file, |file| file.segment_parent_file())
     }
@@ -1564,7 +1564,7 @@ fn dedup_pop<T: Ord>(heap: &mut BinaryHeap<T>) -> Option<T> {
     Some(item)
 }
 
-impl IndexSegment for ReadonlyIndexImpl {
+impl IndexSegment for ReadonlyIndexSegment {
     fn segment_num_parent_commits(&self) -> u32 {
         self.num_parent_commits
     }
@@ -1573,7 +1573,7 @@ impl IndexSegment for ReadonlyIndexImpl {
         self.num_local_commits
     }
 
-    fn segment_parent_file(&self) -> Option<&Arc<ReadonlyIndexImpl>> {
+    fn segment_parent_file(&self) -> Option<&Arc<ReadonlyIndexSegment>> {
         self.parent_file.as_ref()
     }
 
@@ -1678,7 +1678,7 @@ impl IndexSegment for MutableIndexImpl {
         self.graph.len() as u32
     }
 
-    fn segment_parent_file(&self) -> Option<&Arc<ReadonlyIndexImpl>> {
+    fn segment_parent_file(&self) -> Option<&Arc<ReadonlyIndexSegment>> {
         self.parent_file.as_ref()
     }
 
@@ -1816,14 +1816,14 @@ impl<'a> IndexEntry<'a> {
     }
 }
 
-impl ReadonlyIndexImpl {
+impl ReadonlyIndexSegment {
     fn load_from(
         file: &mut dyn Read,
         dir: PathBuf,
         name: String,
         commit_id_length: usize,
         change_id_length: usize,
-    ) -> Result<Arc<ReadonlyIndexImpl>, IndexLoadError> {
+    ) -> Result<Arc<ReadonlyIndexSegment>, IndexLoadError> {
         let parent_filename_len = file.read_u32::<LittleEndian>()?;
         let num_parent_commits;
         let maybe_parent_file;
@@ -1833,7 +1833,7 @@ impl ReadonlyIndexImpl {
             let parent_filename = String::from_utf8(parent_filename_bytes).unwrap();
             let parent_file_path = dir.join(&parent_filename);
             let mut index_file = File::open(parent_file_path).unwrap();
-            let parent_file = ReadonlyIndexImpl::load_from(
+            let parent_file = ReadonlyIndexSegment::load_from(
                 &mut index_file,
                 dir,
                 parent_filename,
@@ -1862,7 +1862,7 @@ impl ReadonlyIndexImpl {
         let overflow_parent = data.split_off(graph_size + lookup_size);
         let lookup = data.split_off(graph_size);
         let graph = data;
-        Ok(Arc::new(ReadonlyIndexImpl {
+        Ok(Arc::new(ReadonlyIndexSegment {
             parent_file: maybe_parent_file,
             num_parent_commits,
             name,
@@ -1935,7 +1935,7 @@ impl ReadonlyIndexImpl {
     }
 }
 
-impl Index for ReadonlyIndexImpl {
+impl Index for ReadonlyIndexSegment {
     fn shortest_unique_commit_id_prefix_len(&self, commit_id: &CommitId) -> usize {
         CompositeIndex(self).shortest_unique_commit_id_prefix_len(commit_id)
     }