[Issue 17318] Delegates allow escaping reference to stack variable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17318

--- Comment #2 from hsteoh at quickfur.ath.cx ---
It could be because the compiler now is smarter about constructing return
values in-place rather than moving the struct afterwards.

Nevertheless, the actual problem still persists: the delegate is closing over a
local variable that resides on the stack. This should have been prevented by
-dip1000, but it doesn't.

Here's slightly more elaborate example that exposes the bug on latest dmd git
master:
---------
import std.stdio;

struct S {
        int x;
        void delegate() dg;
        this(int dummy) {
                dg = () {
                        writefln("&x = %#x", &x);
                        x++;
                };
        }
}

auto makeS() {
        auto s = S(1);
        return s.dg; // <-- N.B. escaping reference to s
}

void smoke(void delegate() dg) {
        int z = 789;

        writeln(z);
        dg();
        writeln(z);
}

void main() {
        auto dg = makeS();
        smoke(dg);
}
---------

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