[Issue 20149] [DIP1000] Local data escapes `opSlice` if not annotated with `return`

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20149

--- Comment #1 from Mike Franklin <slavo5150 at yahoo.com> ---
> Observation-2:  Decorating `opSlice` with `return` causes a compiler error to be correctly emitted where the slice is escaping `foo`

In the example above, that should be `fun`, not `foo`.

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