Command to check that all symbols come from declared packages #598
Description
As far as I understand, with Spago and Purescript it is possible to use data types and functions coming from transitive dependencies (dependencies of declared dependencies).
This may cause problems if my declared dependency decides to remove one of its dependency which I'm using but not declaring.
To avoid such issues, it would be nice to have in Spago a command which checks that every function and every data type used in the project comes from a package declared as a dependency in spago.dhall. Moreover, the same command could check whether some declared dependency is actually not used by the project and could be removed.