MultiplayerSynchronizer fatally crashes when attempting to sync a PackedStringArray

[cridenour]

Godot version

4.0.dev (11abff)

System information

Windows 10

Issue description

Backtrace below: seems related to a type. First failed on alpha13, so updated to master to further test.

CrashHandlerException: Program crashed
Engine version: Godot Engine v4.0.alpha.custom_build (11abffbf1282d457f966741f14aa5a5793f3c208)
Dumping the backtrace. Please include this when reporting the bug on: https://github.com/godotengine/godot/issues
[0] MultiplayerAPI::encode_and_compress_variant (C:\Users\Chris\Development\godot\godot\scene\main\multiplayer_api.cpp:74)
[1] MultiplayerAPI::encode_and_compress_variants (C:\Users\Chris\Development\godot\godot\scene\main\multiplayer_api.cpp:248)
[2] SceneReplicationInterface::_make_spawn_packet (C:\Users\Chris\Development\godot\godot\modules\multiplayer\scene_replication_interface.cpp:298)
[3] SceneReplicationInterface::_update_spawn_visibility (C:\Users\Chris\Development\godot\godot\modules\multiplayer\scene_replication_interface.cpp:234)
[4] SceneReplicationInterface::on_peer_change (C:\Users\Chris\Development\godot\godot\modules\multiplayer\scene_replication_interface.cpp:56)
[5] SceneMultiplayer::_add_peer (C:\Users\Chris\Development\godot\godot\modules\multiplayer\scene_multiplayer.cpp:176)
[6] CallableCustomMethodPointer<SceneMultiplayer,int>::call (C:\Users\Chris\Development\godot\godot\core\object\callable_method_pointer.h:105)
[7] Callable::callp (C:\Users\Chris\Development\godot\godot\core\variant\callable.cpp:51)
[8] Object::emit_signalp (C:\Users\Chris\Development\godot\godot\core\object\object.cpp:991)
[9] Object::emit_signal<int> (C:\Users\Chris\Development\godot\godot\core\object\object.h:818)
[10] ENetMultiplayerPeer::_parse_server_event (C:\Users\Chris\Development\godot\godot\modules\enet\enet_multiplayer_peer.cpp:134)
[11] ENetMultiplayerPeer::poll (C:\Users\Chris\Development\godot\godot\modules\enet\enet_multiplayer_peer.cpp:337)
[12] SceneMultiplayer::poll (C:\Users\Chris\Development\godot\godot\modules\multiplayer\scene_multiplayer.cpp:61)
[13] SceneTree::process (C:\Users\Chris\Development\godot\godot\scene\main\scene_tree.cpp:442)
[14] Main::iteration (C:\Users\Chris\Development\godot\godot\main\main.cpp:2885)
[15] OS_Windows::run (C:\Users\Chris\Development\godot\godot\platform\windows\os_windows.cpp:907)
[16] widechar_main (C:\Users\Chris\Development\godot\godot\platform\windows\godot_windows.cpp:179)
[17] _main (C:\Users\Chris\Development\godot\godot\platform\windows\godot_windows.cpp:203)
[18] main (C:\Users\Chris\Development\godot\godot\platform\windows\godot_windows.cpp:215)
[19] __scrt_common_main_seh (d:\agent\_work\63\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288)
[20] BaseThreadInitThunk
-- END OF BACKTRACE --

Steps to reproduce

A combination of Spawner and Synchronizer, and an unknown additional condition.

I've tried disabling the spawn variables on my synchronizer (via the checkbox) and it did not stop the issue.

I'm happy to run additional debugging but I'm unsure where to focus my efforts. Hoping for some guidance here.

Minimal reproduction project

No response

[Calinou]

@cridenour Please upload a minimal reproduction project to make this easier to troubleshoot.

[cridenour]

@Calinou unfortunately been unable to recreate so far as I'm not sure what the underlying issue is. Basic multiplayer demos run fine, but something about my project is hard crashing between 12 and 13. Happy to put more work, just need some guidance. If nothing else I can bisect master commits until I find the change.

[Calinou]

If nothing else I can bisect master commits until I find the change.

Please do if you have time 🙂

[cridenour]

@Calinou got it! Quite a rabbit hole.

Starting with commit 3084a4 (which is #63219) my project starts to fail.

Here's the offending line in multiplayer_api: https://github.com/godotengine/godot/blob/master/scene/main/multiplayer_api.cpp#L74

Because 3 new variants were added (Vector4, Vector4i and Projection), this hard-coded sanity check fails. It looked out of date before this commit, but this commit moved PackedStringArray into Variant.Type = 34 which is causing the fatal crash.

PR submitted as #64263.