[Issue 16123] alias member of member

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=16123

--- Comment #9 from Nick Treleaven <nick at geany.org> ---
>   S s;
>   alias y = s.x; // note, this compiles just fine, you need to use it to flag the error.

This is an error in the next edition:
https://dlang.org/spec/legacy#alias-instance-member

https://github.com/dlang/dmd/pull/15863

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