Function module_files 

fn module_files(
    path: &Path,
    inline: &[String],
    items: &[Item],
    in_test: bool,
    out: &mut Vec<(PathBuf, bool)>,
)

Collects the candidate files of each out-of-line mod in items, with whether the declaration is under #[cfg(test)]. inline names the inline modules enclosing items. Paths follow the reference’s module-path rules: a #[path] outside inline modules is relative to the file’s directory, and otherwise a module lives under the directory of a mod.rs-style file (lib.rs, main.rs, mod.rs, build.rs, or a crate root under bin, tests, benches or examples), or under one named after any other file.