llvm-cov currently generates a single top-level index HTML file. This is fine for smaller projects, for larger codebases this can lead to scalability issues. For example, in case of Fuchsia the generated index has 12M and rendering this file is causing problems for browsers. To address this issues, we would like to support generating per-directory index files which is also an approach used by lcov. What's not yet clear is whether this mode should be an opt-in controlled by an option or whether this mode should replace the current model.