Below a cut and paste of my original comment in #1603 :

Sorry if I am late at being picky here, but I find the API of do_install growing quite unintuitive. Now we may call a do_install that does no install at all, while the semantic needed for this PR could have been obtained directly in the install command traversing the DAG with or without root and calling an unmodified version of do_install from there.

Moved to an issue as suggested by @citibeth .

@tgamblin Do you think it would be the case to add another tag like 'refactoring' ?