There are 'interface' files in D, too. They are rarely used and usually auto-generated by the compiler, but similar to header files in C. There is no syntactical difference in the content of .di compared to .d, so it can be added as an additional extension to the same mime type.
Author: Bastien Nocera <firstname.lastname@example.org>
Date: Tue Feb 12 15:29:10 2013 +0100
Add *.di as a glob for D interface source files
on Jul 01, 2016 at 02:34:00.
(provided by the Example extension).