Extend the call site default argument expansion mechanism?

[jmh530]

On Tuesday, 15 May 2018 at 15:02:36 UTC, jmh530 wrote:
> [snip]
>

Note, it's not an issue if Foo were not a struct. This was fixed 
in Bug 6400 [1]l. The issue is with template instances. I have 
filed a new enhancement request [2]

[1] https://issues.dlang.org/show_bug.cgi?id=6400
[2] https://issues.dlang.org/show_bug.cgi?id=18863