Constant CHECKED_SRC_ROOTS 

const CHECKED_SRC_ROOTS: &[&str];

Source trees that follow the foo.rs + foo_tests.rs sibling convention and are therefore checked by this command.

Every workspace member’s src/ must appear either here or in UNCHECKED_SRC_ROOTS; every_workspace_member_src_root_is_classified fails the build otherwise. That is the point of splitting the two lists: this used to be a bare allowlist, so a crate that was simply never added to it was silently unchecked, and the command still reported “all source files have a _tests.rs sibling” - a pass that only meant it had not looked.