M1.2: deduplicate font collection offsets early

crates/fonts/src/fontdb.rs

@@ -611,11 +611,11 @@ const MAX_COLLECTION_ENTRIES_SCANNED: u32 = 16_384;
 /// Maximum named instances read from a single face.
 const MAX_NAMED_INSTANCES_PER_FACE: usize = 1024;
 
-fn distinct_face_indices(entries: impl IntoIterator<Item = (u32, usize)>) -> Vec<u32> {
-    let mut directories = std::collections::HashSet::new();
+fn distinct_face_indices(entries: impl IntoIterator<Item = (u32, u32)>) -> Vec<u32> {
+    let mut offsets = std::collections::HashSet::new();
     let mut indices = Vec::with_capacity(MAX_COLLECTION_FACES as usize);
-    for (index, directory) in entries.into_iter().take(MAX_COLLECTION_ENTRIES_SCANNED as usize) {
-        if directories.insert(directory) {
+    for (index, offset) in entries.into_iter().take(MAX_COLLECTION_ENTRIES_SCANNED as usize) {
+        if offsets.insert(offset) {
             indices.push(index);
             if indices.len() == MAX_COLLECTION_FACES as usize {
                 break;
@@ -636,8 +636,10 @@ fn enumerate_faces(data: &[u8]) -> Vec<Found> {
         Ok(FileRef::Font(_)) => vec![0],
         Ok(FileRef::Collection(c)) => {
             let entries = (0..c.len().min(MAX_COLLECTION_ENTRIES_SCANNED)).filter_map(|i| {
-                let f = skrifa::FontRef::from_index(data, i).ok()?;
-                Some((i, f.table_directory().table_records().as_ptr() as usize))
+                let start = 12usize.checked_add((i as usize).checked_mul(4)?)?;
+                let end = start.checked_add(4)?;
+                let offset = u32::from_be_bytes(data.get(start..end)?.try_into().ok()?);
+                Some((i, offset))
             });
             distinct_face_indices(entries)
         }
@@ -1470,7 +1472,7 @@ mod font_dir_tests {
     #[test]
     fn duplicate_collection_offsets_do_not_consume_face_cap() {
         let mut entries = vec![(0, 7); MAX_COLLECTION_FACES as usize];
-        entries.extend((0..MAX_COLLECTION_FACES).map(|i| (i + MAX_COLLECTION_FACES, i as usize + 8)));
+        entries.extend((0..MAX_COLLECTION_FACES).map(|i| (i + MAX_COLLECTION_FACES, i + 8)));
         let faces = distinct_face_indices(entries);
         assert_eq!(faces.len(), MAX_COLLECTION_FACES as usize);
         assert_eq!(faces.first(), Some(&0));