string file = __FILE__ considered harmful (and solution)

[FeepingCreature]

There's a very common idiom where in order to report line numbers 
of an error or a log line at the callsite of a function, you pass 
__FILE__ and __LINE__ as default parameters:

void foo(string file = __FILE__, size_t line = __LINE__);

What's wrong with this?

Say you add a string parameter, such as

void foo(string msg, string file = __FILE__, size_t line = 
__LINE__);

foo("Hello World");

Now when you accidentally grab an old version of the library, 
your new code will still run, but it will believe that it's being 
called from file "Hello World", line 15. Not good.

Luckily there's a fix. Just stick this in some common header file 
in your project:

struct CallerInfo
{
   string file;
   size_t line;
}

void foo(string msg, CallerInfo caller = CallerInfo(__FILE__, 
__LINE__));

Now you cannot accidentally invoke foo with a string, or in fact 
any type except another instance of CallerInfo.

This is such a basic type that it really belongs in phobos, 
arguably object.d. At which point we can shorten this to 
CallerInfo caller = __CALLER__, and be forward compatible for 
additional information about the callsite, such as, say, 
attributes of the calling function.