Function module_surface 

pub fn module_surface(
    dir: &Path,
    deps: &DependenciesCfg,
    resolved: &ResolvedModules,
) -> ModuleSurface

What the modules in deps register for scripts, read the way a run reads it: each is installed into a scratch app, in headless mode, by the loader a run uses, and its registrations are taken back out. A module compiled into this binary answers from there, and any other is opened from disk, so the surface is the one the app’s run binds to.

dir is the app directory and resolved what the compiler resolved for the version sources. A module that does not load prints the loader’s banner and registers nothing, so a call into it fails the compile that follows.