[Issue 17927] [scope] scope input return value can be escaped

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17927

--- Comment #4 from Walter Bright <bugzilla at digitalmars.com> ---
It turns out that:

  struct String {
    inout(char)* mem2() inout scope @safe { return ptr; }
    char* ptr;
  }

not issuing an error is actually correct, because a parameter that is `ref
inout` is inferred to be `return`, and the `this` parameter for `mem2` is `ref
inout`.

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