Crash turning off Hack Gravity

[lpgagnon]

    @   00007FFAC11D443F  	google::LogMessageFatal::~LogMessageFatal [0x00007FFAC11D443E+46]
    @   00007FFA857A50C1  	principia__VesselVelocity [0x00007FFA857A50C0+1050160]
    @   00007FFA85675877  	principia__InsertUnloadedPart [0x00007FFA85675876+646]
    @   000001AC8E03F277  	(No symbol) [0x000001AC8E03F276]
F0701 18:24:55.874464  5856 plugin.cpp:1653] Check failed: inserted part_id: 64777563

First seen in Heine, consistently reproducible in Hesse. logs-3388.zip: logs & journal

Steps: (have not tried to reduce to minimal repro case)

• place vessel in orbit (via KCT Sim)
• enable Hack Gravity
• decouple, turning the 1 vessel into 2 vessels
• go to 10x time warp
• turn off Hack Gravity
  -> game immediately freezes, goes to desktop after a few seconds

[lpgagnon]

I've just accidentally confirmed this is still a thing in ‎𓇹𓄟𓋴𓏲

[pleroy]

This is still a thing because to be honest I never looked into it. A problem with "hack gravity" falls into the category "Doctor, it hurts when I do this!".

But you piqued my curiosity, so I tried, and indeed the reproduction steps above work. Now I am baffled.

I have a vessel with 3 parts: a pod, a decoupler, and a service bay (that's about as complex a vessel as I am capable of building). After decoupling I have the pod on one side and the decoupler + service bay on the other side. When "hack gravity" is turned off, the following happens:

1. A vessel is inserted which, from its name, looks to be the "main" vessel. The following parts are inserted in that vessel:
   1.1 The pod.
   1.2 The decoupler.
   1.3 The service bay.
2. A second vessel is inserted, which is named "debris". The following parts are inserted in that vessel:
   2.1 The decoupler. (This is where it 💥.)
   2.2 The service bay.

The steps in bold (1.2 and 1.3) look wrong. It should not be possible for a part to belong to two vessels. I suspect that we have a case of KSP being incapable of maintaining its own invariants.

I have no idea how we can/should handle that madness. @eggrobin will need to look into this.