[Issue 23598] Another nasty forward reference bug

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23598

--- Comment #6 from Walter Bright <bugzilla at digitalmars.com> ---
What seems to be happening is the first time it goes through `template sort`,
it cannot set `aliasdecl` because the two `alias sort` assignments are hidden
behind conditional compilation.

Hence `aliasdecl` is null.

So, in semantic for `struct String` it encounters `SortedItems.length`. The
`aliasdecl` is null, so `SortedItems` becomes `sort!(...)` which becomes `void`
and there is no `length` for `void`.

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