FishNet ILPP crash due to copied parameter/custom-attribute metadata not being imported

[MarkZeroK]

Environment:

• Unity: 6000.3.10f1
• FishNet: 4.6.22

Discord link: https://discord.com/channels/424284635074134018/1034477094731784302/1480963733466648586

Observed behavior:
FishNet ILPP crashes during compilation while processing Assembly-CSharp.dll. Cecil throws:
System.ArgumentException: Member 'System.Void System.ParamArrayAttribute::.ctor()' is declared in another module and needs to be imported

Expected behavior:
FishNet ILPP should complete normally.

Steps to repeat:
Did not find a simple way to repeat this. It just one day started happening in my project after adding a C# event to one class. Tried to create a simple project and make it happen there but could not get it to repeat. Other users seem to have had the same or similar issue but it seems to have thus far been dismissed as a Unity bug, see https://github.com/FirstGearGames/FishNet/issues?q=ILPP

Root cause:
Compilation fails in FishNet ILPP during generated method/parameter copying. FishNet codegen appears to reuse Cecil ParameterDefinition, CustomAttribute, and some generic parameter metadata directly instead of cloning/importing it into the destination module. If a copied parameter carries ParamArrayAttribute, Cecil fails while writing metadata.

Fix:
I was able to create if not a complete fix (not tested very well yet), at least a workaround. I patched FishNet locally to clone/import parameter definitions, custom attributes, and generic parameter metadata instead of reusing Cecil objects. After that, my project compiled successfully and everything seems to work when testing it.

I have added the patch diff of my changes to FishNet as an attachment to this issue.

FishNet ILPostProcessor error fix.patch

[FirstGearGames]

Thanks for these changes. This has been an issue for some time that was assumed as a Unity bug because it would randomly appear, then disappear on the same user code. The circumstances at which it went away were unusual, sometimes just creating a new file and then deleting it, clearing cache, so on.

The patch file is set for FishNet as a package file, when the git uses an Assets working directory; I copied the changes manually into the upcoming release to compensate for this.

[FirstGearGames]

Resolved in 4.7.0.