Proposal?

[FeepingCreature]

On Wednesday, 30 May 2018 at 08:27:16 UTC, FeepingCreature wrote:
> struct CallerInfo
> {
>   string file;
>   size_t line;
> }

Let me try to flesh this out.

void foo(CallContext caller = __CALL_CONTEXT__)
{
}

// in druntime object.d
struct CallContext
{
   public size_t line; // expected to change for every call
   private const FunctionContext* functionContext; // expected to 
be constant for many calls
   alias functionContext this;
}

/** a variable with this type is lazily allocated once per 
function */
struct FunctionContext
{
   string file, fileFullPath, module, function, prettyFunction;
}

I've looked at DMDFE and I don't think I know enough to do this, 
annoyingly.