Function module_key 

pub fn module_key(spelling: &Path, lint: Option<&str>) -> Key

The key for one module in this invocation.

spelling is the path as the CLI will hand it to the checker, not a resolved one: the checker echoes it into every diagnostic it prints, so htl check . and htl check src/a.tl produce different text for the same module and cannot share an entry. The working directory completes it, since the same relative spelling means a different file from somewhere else.