[cfe-dev] [Patch] Diagnose unused declaration

[Ted Kremenek]

On Jan 3, 2009, at 11:14 AM, EdB wrote:

>> Looks good. There seems to be a whitespace issue in
>> ActOnEndOfTranslationUnit.
>
> Pleased find attached a new version:
> It fixed some crash.
> Unused warning is no longer actived by default. You should enable it
> with -Wunused_declaration

I'm not certain that the approach here will work.  Since an  
IdentifierInfo is not unique to a declaration using a bit in  
IdentifierInfo to perform this check will be ineffective in many  
cases.  For example:

void f() {
   int x = ...
   x++;
}

void g() {
    int x;   // no warning will be issued
}

The other thing that bothers me about this is putting this bit in  
IdentifierInfo in the first place.  It seems like a very invasive  
thing to do for a simple check like this, especially one that isn't  
always used.  Generally we like to keep such information "on the side"  
unless there is a good reason not to.  Why not use a DenseSet to keep  
track (on the side) of what declarations are used?  You can then do  
this on a declaration based (i.e., for a particular NamedDecl) rather  
than using IdentifierInfo's in this conflated way.