Dragging a waveform from one group to another causes a crash

[timp3289]

Windows 11, compiled with MSYS2 UCRT64 gcc
OK on release v0.1.1
Crashes on version compiled from recent (~2 days old) source.

To reproduce:

Open:
sparse.scopesession.zip

Arm the trigger
Drag the waveform Add_2 into the plot with ACRMS_1.trend and ACRMS_4.trend

(crash)

Crash info:

C:/msys64/ucrt64/include/c++/15.2.0/bits/stl_vector.h:1263: constexpr std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = std::shared_ptr<DisplayedChannel>; _Alloc = std::allocator<std::shared_ptr<DisplayedChannel> >; reference = std::shared_ptr<DisplayedChannel>&; size_type = long long unsigned int]: Assertion '__n < this->size()' failed.
gdb: unknown target exception 0xc0000409 at 0x7ffc14fe4ace

Thread 1 received signal ?, Unknown signal.
0x00007ffc14fe4ace in ucrtbase!abort () from C:\WINDOWS\System32\ucrtbase.dll

Backtrace:

(gdb) bt
#0  0x00007ffc14fe4ace in ucrtbase!abort () from C:\WINDOWS\System32\ucrtbase.dll
#1  0x00007ffb5fc6a2fb in ?? () from C:\msys64\ucrt64\bin\libstdc++-6.dll
#2  0x00007ff6676bb577 in std::vector<std::shared_ptr<DisplayedChannel>, std::allocator<std::shared_ptr<DisplayedChannel> > >::operator[] (this=0x180dcf48, __n=0)
    at C:/msys64/ucrt64/include/c++/15.2.0/bits/stl_vector.h:1263
#3  0x00007ff6674e6c68 in WaveformArea::GetStream (this=0x180dcf10, i=0)
    at C:/msys64/home/tim/repos/scopehal-apps/src/ngscopeclient/WaveformArea.h:480
#4  0x00007ff6674ba7fa in WaveformGroup::Render (this=0x181141f0)
    at C:/msys64/home/tim/repos/scopehal-apps/src/ngscopeclient/WaveformGroup.cpp:257
#5  0x00007ff6673c4a97 in MainWindow::RenderUI (this=0x2f64660)
    at C:/msys64/home/tim/repos/scopehal-apps/src/ngscopeclient/MainWindow.cpp:705
#6  0x00007ff66748f987 in VulkanWindow::Render (this=0x2f64660)
    at C:/msys64/home/tim/repos/scopehal-apps/src/ngscopeclient/VulkanWindow.cpp:623
#7  0x00007ff6673c0e11 in MainWindow::Render (this=0x2f64660)
    at C:/msys64/home/tim/repos/scopehal-apps/src/ngscopeclient/MainWindow.cpp:554
#8  0x00007ff6674c95cf in main (argc=1, argv=0x803fe0)
    at C:/msys64/home/tim/repos/scopehal-apps/src/ngscopeclient/main.cpp:320

Compiled with MSYS UCRT64, CMAKE_BUILD_TYPE=debugnoopt and launched from gdb

tim@TIMSPC UCRT64 ~/repos/scopehal-apps
$ gcc --version
gcc.exe (Rev8, Built by MSYS2 project) 15.2.0
Copyright (C) 2025 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Version info:

tim@TIMSPC UCRT64 ~/repos/scopehal-apps
$ git submodule status
 6c4d9be819baddddc76d8e567574827b9959a14d doc (6c4d9be)
 4e122b687f25f3daeacddbfa8fe395236983ad4e lib (heads/master)
 2917cd9ec120bce7b4297e7f3afb660071707e05 src/ImGuiFileDialog (v0.6.4-75-g2917cd9)
 3ef1e5c131fffc521828b6c7ee90f6685da430c5 src/imgui (heads/docking)
 6047a3b2cce1f4fbc9e814b71da29eb9cbd7f650 src/imgui-node-editor (heads/master)
 3914f24ddd3a6369308efd48dfcace3bc6096783 src/imgui_markdown (3914f24)
 6db343ad341ba2d7166f1a71b5b182a380e5bc08 src/nativefiledialog-extended (v1.2.1-10-g6db343a)

tim@TIMSPC UCRT64 ~/repos/scopehal-apps
$ git log
commit 19697ef2485280a13c31b8bc98b780e8b704a7ce (HEAD -> master, tag: v0.0.0, origin/master, origin/HEAD)
Author: Andrew D. Zonenberg <azonenberg@drawersteak.com>
Date:   Tue Apr 7 11:14:15 2026 -0700

    Updated to latest scopehal

commit 7b37c6749fd76911d54fe5342adc5c2c1137242b
Author: Andrew Zonenberg <azonenberg@drawersteak.com>
Date:   Mon Apr 6 09:17:00 2026 -0700

    Updated to latest submodules