// Protocol value as a field of a wrapper struct, constructed from a stack
// local inside a function and appended to a `List`. The payload must be
// heap-copied so dispatch survives the constructing function returning.

#import "modules/std.sx";

Sizable :: protocol {
    size :: () -> s64;
}

Widget :: struct { value: s64; }
impl Sizable for Widget {
    size :: (self: *Widget) -> s64 { self.value; }
}

// Wrapper struct with a protocol field (like ViewChild)
Item :: struct {
    view: Sizable;
}

Container :: struct {
    items: List(Item);

    add :: (self: *Container, w: Widget) {
        p := w;  // local copy
        self.items.append(Item.{ view = p });  // protocol created from stack local `p`

        // Works here: stack local `p` is still alive
        out("inside add: ");
        print("{}\n", self.items.items[self.items.len - 1].view.size());
    }
}

main :: () -> void {
    c : Container = .{};
    c.add(Widget.{ value = 42 });
    c.add(Widget.{ value = 99 });

    // BUG: items[0] should return 42, but returns 99 (reads items[1]'s stack slot)
    // Both protocol values point to the same stack address (the `p` local in add())
    r0 := c.items.items[0].view.size();
    r1 := c.items.items[1].view.size();
    print("items[0] = {} (expected 42)\n", r0);
    print("items[1] = {} (expected 99)\n", r1);

    // With more stack activity between add() and the reads, this crashes
    // (stack memory overwritten by other function calls)
}