[dmd-internals] How not to report unused identifiers

[cy via dmd-internals]

Well, Module in dmodule.d has a list called "members" returned 
from parsing the code, each item a symbol that's supposedly a 
member of that module. But, the list also includes template 
specializations and package names, which are apparantly never 
searched for?

In dmd, I made a bool[const(char)*] searched array in the Module 
class, and added to that a symbol's "toChars" representation 
every time it was searched for in that module. Then, in the third 
pass (was that a mistake?) I compared every item in 
Module.members to see if its toChars representation was in that 
array. If not, it warns about an unused identifier.

So, it searched for like 5 symbols, and there were 2000 symbols 
give or take in the members array, resulting in a wall of text of 
unused identifiers, that are actually used I'm sure, but I have 
no idea how to determine that, if they're never looked up.