Control size of environment trees generated from modules #2674
Description
Depends on #2540 .
To generate the environment for a module, we use restrictEnv to take the runtime environment and restrict it to only those names which are supposed to be exported from the module. The resulting Map is much smaller, of course, but environments also use a tree structure to record the sequence of operations that was used to construct them, including deletion. So I am afraid that the tree structures for module environments are going to be very large --- they will mention everything that was in the environment before and then everything that was deleted.
We should (1) investigate whether this is, in fact, the case (and how big of a problem it is), and (2) think of ways to mitigate it, if it is a problem.