Core dump attempting to use wesnoth.print_attributes on stacked_widget

[white-haired-uncle]

Game and System Information

• Version:
  Battle for Wesnoth v1.19.0-dev (ebe84ce5e68-Modified) <unknown>

• OS:
  Linux spartan 5.15.0-97-generic #107-Ubuntu SMP Wed Feb 7 13:26:48 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux

Description of the bug

wesnoth: src/gui/auxiliary/iterator/policy_order.hpp:266: bool gui2::iteration::policy::order::top_down<VW, VG, VC>::next() [with bool VW = true; bool VG = true; bool VC = true]: Assertion `root_' failed.
Abort(coredump)

On a forum post I saw mention of a stacked_widget which I thought might help me with a problem, but seems to have no documentation I can find. So I thought I'd see if I could weasel some clues out of wesnoth.print_attributes(). It didn't work, and I'm not at all surprised since I have absolutely no idea what I'm doing, but I crashed wesnoth so here I am.

function wesnoth.wml_actions.stacked_widget_gui()
        local dialogDefinition = {
                wml.tag.tooltip { id = "tooltip_large" },
                wml.tag.helptip { id = "helptip_large" },
                wml.tag.grid {  wml.tag.row { wml.tag.column {
                        wml.tag.stacked_widget {
                                id = "stacker",
                                T.layer {
                                        T.row { T.column { T.label { label = "Hello world" } } }
                                }
                        }
                } } }
        }

        local function preshow(dialog)
                wesnoth.print_attributes(dialog.stacker)
                gui.show_lua_console()
        end
        gui.show_dialog(dialogDefinition,preshow)
end

Steps to reproduce the behavior

1. Install attached scenario.
2. Use right click menu "stacked_widget_gui"

GUI_Tutorial.tar.gz

Expected behavior

An error message with some idea of the (first) error would be preferable.

Additional context

Please change the title to something useful. I have no idea what it would be at this point, but didn't want to just put "core dump".

[white-haired-uncle]

Okay, figured out one thing. If I comment out wesnoth.print_attributes(dialog.stacker) it runs and I see "Hello world" displayed.

I also added an id to the label and ran wesnoth.print_attributes(dialog.my_label) and got something that looks more or less correct (to the best of my understanding).

[CelticMinstrel]

Got a stack trace. This is the relevant portion.

#4	0x00000001003bb55d in gui2::iteration::policy::order::top_down<true, true, true>::next() at wesnoth/src/gui/auxiliary/iterator/policy_order.hpp:266
#5	0x0000000100351628 in gui2::iteration::iterator<gui2::iteration::policy::order::top_down<true, true, true> >::next() at wesnoth/src/gui/auxiliary/iterator/iterator.hpp:77
#6	0x0000000100351049 in lua_widget::impl_widget_dir(lua_State*) at wesnoth/src/scripting/lua_widget_attributes.cpp:605
#7	0x0000000102889de7 in precallC(lua_State*, StackValue*, int, int (*)(lua_State*)) at wesnoth/src/modules/lua/ldo.c:529
#8	0x0000000102889ea2 in luaD_precall(lua_State*, StackValue*, int) at wesnoth/src/modules/lua/ldo.c:595
#9	0x000000010288a1d5 in ccall(lua_State*, StackValue*, int, unsigned int) at wesnoth/src/modules/lua/ldo.c:635
#10	0x000000010288a248 in luaD_callnoyield(lua_State*, StackValue*, int) at wesnoth/src/modules/lua/ldo.c:655
#11	0x0000000102879c8f in f_call(lua_State*, void*) at wesnoth/src/modules/lua/lapi.c:1038
#12	0x00000001028888b1 in luaD_rawrunprotected(lua_State*, void (*)(lua_State*, void*), void*) at wesnoth/src/modules/lua/ldo.c:144
#13	0x000000010288a923 in luaD_pcall(lua_State*, void (*)(lua_State*, void*), void*, long, long) at wesnoth/src/modules/lua/ldo.c:953
#14	0x0000000102879b56 in lua_pcallk(lua_State*, int, int, int, long, int (*)(lua_State*, int, long)) at wesnoth/src/modules/lua/lapi.c:1064
#15	0x000000010148e96e in dir_meta_helper(lua_State*, std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > >&) at wesnoth/src/scripting/lua_kernel_base.cpp:536
#16	0x000000010148e629 in luaW_get_attributes(lua_State*, int) at wesnoth/src/scripting/lua_kernel_base.cpp:632

In short, iterating through a stacked widget is broken for some reason. It might be as simple as "someone forgot to implement the visitor methods" but I haven't looked any closer at it.