How to create nogc code?

[Adam Sansier via Digitalmars-d-learn]

So, I have to create some nogc code. Basically all it uses is 
idup to create a string that is passed as a return value. It 
seems this is necessary or the string will be reused and 
corrupted.

idup uses the gc, I am currently just malloc'ing the string and 
allowing for the memory leak. This is somewhat acceptable given 
that this code should rarely be called and generally only at 
startup. It will generally waste only a few KB of memory.

Regardless, is there a better way to do this that avoids the gc 
and doesn't potentially leak considerably?  Currently the only 
option is to notify the user through comments on the function 
that it leaks and should carefully be used.

Ultimately a struct is built which includes these strings(which 
is partly the corruption issue without idup).

How does phobos deal with this type of stuff? Does it force the 
user to allocate the memory so they are at least aware that they 
have to control it?