@dtolnay I couldn’t find anything in the docs for typetag, inventory or ctor on why any of this needs to be implemented with life-before/after-main instead of making the client app write something like typetag::init() in main().
Is the life-before-main stuff “just” to enable writing libraries that don’t virally “infect” all transitive dependents and their client apps with a need to explicitly init() the library in main()? Could this be controlled by cargo features? Is the inadequacy of cargo features for transitive dependency config (ping @kornel) a factor here? etc.