Why is the identifier "printf" known by the frontend?

[Frits van Bommel]

BCS wrote:
> Walter Bright wrote:
>> Wolfgang Draxinger wrote:
>>> What is the reason for that? "import std.stdio" is not a real
>>> difficult thing to type.
>>
>> Because I find it verrryy handy in writing minimal test cases. 
>> writefln, in order to work, requires much of D and Phobos to be 
>> working properly. printf, being part of the C library, doesn't require 
>> any of Phobos and very little of D to work, so it's handy when things 
>> are broken.
> 
> Could this be put under a compiler switch?
> 
> -dbg    compiler debug mode

Or just -debug=PhobosDebug (or whatever).
No compiler modifications necessary.
Of course, this should be turned off for the Phobos binary distributed 
with the compiler.