DIP-1000 scope analysis doesn't kick in for small-size-optimized GC-string

[Per Nordlöw]

On Thursday, 19 April 2018 at 17:36:19 UTC, Per Nordlöw wrote:
> However, I'm having problems within making lifetime analysis 
> via scope kick in. For instance, the function `f` at
>
> https://github.com/nordlow/phobos-next/blob/master/src/sso_string.d#L219

Note that qualifying `opSlice` as `inout` doesn't help.