Stack installed and profile virtuals. Preference for virtuals decreases from left to right. Order of preference: 1. installed and in profile 2. installed only 3. profile only
Initialize _treeVirtuals from the given vartree. It must not have been initialized already, otherwise our assumptions about immutability don’t hold.
Read the ‘virtuals’ file in all profiles.
This updates the preferences for old-style virtuals, affecting the behavior of dep_expand() and dep_check() calls. It can change dbapi.match() behavior since that calls dep_expand(). However, dbapi instances have internal match caches that are not invalidated when preferences are updated here. This can potentially lead to some inconsistency (relevant to bug #1343).
Computes self._virtuals if necessary and returns it. self._virtuals is only computed on the first call.
Initialize _treeVirtuals if it hasn’t been done already. This is a hack for consumers that already have an populated vartree.