actively_find_funcs: Try harder to find functions that are called

Description

We try to load imported and depended packages and search their namespaces as well.

actively_find_funcs(map, funcs)

map

Function map.

funcs

Character vector, functions to find.

For this we need to install the package to a temporary directory, and load it. If this is not possible, a warning is given.

We asume that the trivial search in imported packages and base packages did not work, so we don't try it again.