Unused variables, better as error or warning?

[Walter Bright]

Jonathan M Davis wrote:
> I'm sure that there are cases where it would be nice for 
> the compiler to point out that you're uselessly assigning to a variable 
> (especially if you're making a useless function call too), but it would cost the 
> compiler too much in complexity and cost the programmer in many other cases by 
> forcing them to either ignore warnings (which they should pretty much never do) 
> or throw in pointless explicit initializations rather than letting the defaults 
> do their job.

Having such be errors (or warnings) makes for a very annoying experience. For 
example, when you're commenting out code trying to find a problem, or when 
you're generating D source code from some DSL, etc., having unused variables or 
assignments happen often.