[Issue 22563] Nested structs, if not escaping, shouldn't allocate context (just like delegates)

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22563

--- Comment #2 from Stanislav Blinov <stanislav.blinov at gmail.com> ---
It should in @safe code, which is where `scope` matters. The only way to escape
it should be to break @safe. Isn't that the whole point?..

void* global;

struct Escapist(T)
{
    T value;
}

@safe
void consumeThingWithContext(S)(scope S s)
if (is(S == struct) && __traits(isNested, S))
{
    import core.lifetime;
    global = s.tupleof[$-1];       // error: scope variable `s` assigned to
non-scope `global`
    global = move(s.tupleof[$-1]); // error: scope variable `s` assigned to
non-scope `global`

    auto escape = new Escapist!S(s); // with dip1000: scope variable `s` may
not be copied into allocated memory
}

@safe /*@nogc*/
void main()
{
    int a;
    struct Nested { ~this() @nogc { a++; } }
    consumeThingWithContext(Nested());
}

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