Extensions are optional, and so is their iteration (#293)

Author: Byron

git-index/src/decode.rs

@@ -1,4 +1,4 @@
-use crate::{extension, State};
+use crate::{extension, Entry, State, Version};
 use filetime::FileTime;
 use git_hash::Kind;
 
@@ -79,10 +79,15 @@ impl State {
         // Note that we ignore all errors for optional signatures.
         match start_of_extensions {
             Some(offset) => {
-                ext = load_extensions(&data[offset..], object_hash);
+                let (ext, entries) =
+                    git_features::parallel::join(|| load_extensions(&data[offset..], object_hash), || ());
                 todo!("load all extensions in thread, then get IEOT, then possibly multi-threaded entry parsing")
             }
-            None => todo!("load entries singlge-threaded, then extensions"),
+            None => {
+                let (entries, data) = load_entries(version, data, num_entries, object_hash)?;
+                let ext = load_extensions(data, object_hash);
+                todo!("load entries singlge-threaded, then extensions")
+            }
         }
 
         Ok(State {
@@ -93,19 +98,31 @@ impl State {
     }
 }
 
+fn load_entries(
+    version: Version,
+    beginning_of_entries: &[u8],
+    num_entries: u32,
+    object_hash: git_hash::Kind,
+) -> Result<(Vec<Entry>, &[u8]), Error> {
+    todo!("load entries")
+}
+
 fn load_extensions(beginning_of_extensions: &[u8], object_hash: git_hash::Kind) -> Extensions {
-    let extensions = extension::Iter::new_without_checksum(beginning_of_extensions, object_hash);
-    let mut ext = Extensions::default();
-    for (signature, ext_data) in extensions {
-        match signature {
-            extension::tree::SIGNATURE => {
-                ext.cache_tree = extension::tree::decode(ext_data, object_hash);
+    extension::Iter::new_without_checksum(beginning_of_extensions, object_hash)
+        .map(|extensions| {
+            let mut ext = Extensions::default();
+            for (signature, ext_data) in extensions {
+                match signature {
+                    extension::tree::SIGNATURE => {
+                        ext.cache_tree = extension::tree::decode(ext_data, object_hash);
+                    }
+                    extension::end_of_index_entry::SIGNATURE => {} // skip already done
+                    _unknown => {}                                 // skip unknown extensions, too
+                }
             }
-            extension::end_of_index_entry::SIGNATURE => {} // skip already done
-            _unknown => {}                                 // skip unknown extensions, too
-        }
-    }
-    ext
+            ext
+        })
+        .unwrap_or_default()
 }
 
 #[derive(Default)]

git-index/src/extension/mod.rs

@@ -84,14 +84,17 @@ mod iter {
             }
         }
 
-        pub fn new_without_checksum(data_at_beginning_of_extensions: &'a [u8], object_hash: git_hash::Kind) -> Self {
+        pub fn new_without_checksum(
+            data_at_beginning_of_extensions: &'a [u8],
+            object_hash: git_hash::Kind,
+        ) -> Option<Self> {
             let end = data_at_beginning_of_extensions
                 .len()
-                .checked_sub(object_hash.len_in_bytes())
-                .expect("someone asserted that there is at least one extension");
+                .checked_sub(object_hash.len_in_bytes())?;
             Iter {
                 data: &data_at_beginning_of_extensions[..end],
             }
+            .into()
         }
     }
 

git-index/src/lib.rs

@@ -55,6 +55,9 @@ pub enum Version {
     V4 = 4,
 }
 
+/// An entry in the index, identifying a non-tree item on disk.
+pub struct Entry;
+
 /// An index file whose state was read from a file on disk.
 pub struct File {
     pub state: State,

git-index/tests/file/mod.rs

@@ -18,4 +18,8 @@ mod init {
         let file = file("v2_more_files");
         assert_eq!(file.version(), Version::V2);
     }
+
+    #[test]
+    #[ignore]
+    fn read_without_any_extension() {}
 }