Function reexport_conflicts 

fn reexport_conflicts(
    content: &str,
    entries: &[ReexportEntry],
) -> Result<(), String>

Refuse the re-exports of entries that can’t be written, all in one message: a name re-exported from two packages (a package exports one object under a name), and a name that content, the assembled wrappers, also binds at top level or exports. The package’s own binding would hide the imported one inside its namespace, so export(name) would export it instead; an export alone repeats the one the re-export writes.

Only the generated wrappers are read, not the package’s hand-written R files.