Oh, the amalgamated file is $ROOT/roaring.c instead of src/roaring.c. The .gitignore file functions correctly in Git, but tools like fd and ripgrep somehow also ignore src/roaring.c. It will work if we explicitly specify them like this in .gitignore:
_Originally posted by @amosbird in https://github.com/RoaringBitmap/CRoaring/pull/179#discussion_r1654803111_