DIP60: @nogc attribute

[via Digitalmars-d]

Here's another thing that should be allowed that doesn't depend 
on optimizations:

Any code path in a @nogc function that is guaranteed to abort the 
program should be exempt from @nogc enforcement. This includes 
assert(0) and throwing an Error.

Take std.exception.assumeWontThrow() as an example:

T assumeWontThrow(T)(lazy T expr,
                      string msg = null,
                      string file = __FILE__,
                      size_t line = __LINE__) nothrow
{
     try
     {
         return expr;
     }
     catch(Exception e)
     {
         immutable tail = msg.empty ? "." : ": " ~ msg;
         throw new AssertError("assumeWontThrow failed: Expression 
did throw" ~
                               tail, file, line);
     }
}

Currently, this cannot be @nogc, because it uses `new` and `~`. 
However, this only happens in preparation to throwing the 
AssertError, which in turn causes the program to abort. I guess 
in this situation, it's ok to allocate on the GC heap.

With my proposed rule, assumeWontThrow can be deduced to be @nogc 
iff expr is @nogc. This allows more functions to be @nogc.