I'm writing a crate that uses thread_local! and lazy_static! variables. If this crate is duplicated in the dependency graph, functions risk being called with non-up-to-date global variables, and Bad Things™ (though hopefully no unsafe, but panics for almost certain) will ensue.

As a consequence, I wonder if there could a way for a crate to ask cargo not to allow to pull it twice in the dependency tree. Maybe a do-not-pull-twice attribute on the crate that could be overridden by a --yes-pull-this-twice… something to at least error against the common case of unwillingly pulling a dependency that's brittle in this regard? :)