[Issue 19721] Cannot take address of scope local variable even with dip1000 if a member variable is a delegate

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19721

ag0aep6g <ag0aep6g at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |ag0aep6g at gmail.com

--- Comment #1 from ag0aep6g <ag0aep6g at gmail.com> ---
As far as I understand, it's correct that the code is rejected. `scope` only
provides one level of protection. That means, you can't return a `scope`
pointer, but you can dereference it, make a copy of the pointee, and return
that.

In the example, `func` is allowed to return `*clientData`, regardless of what
happens anywhere else in the code. And since `s` is `scope`, `s.dg` might rely
on references to the stack. So to avoid a leak, you can't be allowed to call
`func` on `s`.

In code:

----
Struct g;

void main() @safe {
    main2();
    () { int[10] stompy = 13; } ();
    g.dg(0); /* Prints "13". We've got memory corruption. */
}

void main2() @safe {
    int stack;
    scope s = Struct();
    s.dg = (int x) @safe { import std.stdio; writeln(stack); };
    () @trusted { func(&s); } (); /* Let's pretend this works in @safe. */
}

private struct Struct {
    void delegate(int) @safe dg;
}

void func(scope Struct* clientData) @safe nothrow {
    g = *clientData;
}
----

(In reply to Atila Neves from comment #0)
> It compiles if the `dg` member variable is removed or replaced with, say, an
> int.

An int doesn't have any indirections, unlike a delegate.

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