[dmd-internals] How not to report unused identifiers

[Daniel Murphy via dmd-internals]

So, a few thoughts:

- bool[const(char)*] will be indexed by the pointer address by
default, not the value of the string.  bool[const(char)[]] should
work.
- toChars is not great for this.  Using the mangled name would be better
- Not every symbol that is used will have an identifier search done
for it.  Sometimes they will be cached as members of some ast class
and referenced directly.  Doing a walk of the post-semantic AST to
build the referenced list might be better.  See what the json emission
does for an example of a post-semantic walk, although that doesn't
walk expressions (which you'd need to do).

On Wed, Mar 30, 2016 at 8:11 AM, cy via dmd-internals
<dmd-internals at puremagic.com> wrote:
> 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.
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