Strange DMD Assertion failure

[Walter Bright]

Chris Miller wrote:
> Compiling code that worked fine with DMD 0.160 now fails on DMD 0.161 
> with the following compiler error:
>    Assertion failure: 'next' on line 2226 in file 'mtype.c'
> 
> Looking at mtype.c I notice the assert makes sure 'next' is not null, 
> but on the next line it checks 'next' for null and acts appropriately; 
> also, in the same function of DMD 0.160 this null check is not there, 
> only the assert, so it leads me to believe that perhaps the new compiler 
> now allows a null 'next' but the assert was left accidentally.
> 
> I tried simplifying my code to make a small reproducable example, but 
> this project is huge and the changes were causing template mixin forward 
> reference errors. Compiling with -v shows it fails on the first semantic 
> pass.

There's no way to track this down without a reproducible test case.