Mysterious build exceptions with no StackTrace | Official Unity Discord | Page 1

deep quest Dec 8, 2025, 12:14 PM

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Hey, I'm continously getting two build errors in a big project with no way to debug them. Both from BuildPlayer in our PreBuildFunction.

The first is Assertion failed on expression: 'classAndNamespaceIndex.size() == 0', with no stacktrace other than BuildPlayer, presumably in some native code somewhere.
The second is:

ArgumentException: assemblyName
UnityEditor.RuntimeClassRegistry.AddSerializedClass (System.String assemblyName, System.String className) (at <41a751bfaf1d44859e9ae4cd25bf88bf>:0)
UnityEditor.DefaultBuildMethods:BuildPlayer(BuildPlayerOptions)

Which when I put a breakpoint on, shows UnityEngine.Events.UnityEvent`1 not having a set assembly-name, with the main part being within native code. I have 0 idea how to figure out what to actually do to fix this or how to make a smaller repro of it, does anybody have any ideas whatsoever? My current theory is an UnityEvent in a Serializable struct somewhere, but no idea how I'd even figure out where that is

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This is an IL2CPP windows dev build with profiling support

dawn stirrup Dec 8, 2025, 1:11 PM

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deep quest Hey, I'm continously getting two build errors in a big project with no way to de...

Is the className argument not visible? Or is it empty as well?
or is it the UnityEngine.Events.UnityEvent1 thing?

I'd also check the editor logs. They might have more info not printed to console.

deep quest Dec 8, 2025, 1:22 PM

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dawn stirrup Is the `className` argument not visible? Or is it empty as well? or is it the `U...

it's the UnityEvent thing, it's how classes with one type argument are shown in reflection

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EditorLog had nothing different unfortunately

dawn stirrup Dec 8, 2025, 1:46 PM

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My hunch is that this has something to do with conditional compilation.
Maybe try searching for all instances of #if or #if UNITY_EDITOR and check if there are any blocks taht contain unity events.

deep quest Dec 8, 2025, 2:08 PM

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Finally figured it out, turned out to be a UnityEvent with a tuple in it, meaning serialized field with nested type arguments. Found it in this forum post from 2022, which means it's stayed unfixed for 3 years without any form of additional logging added to make it easier to find -_-
https://discussions.unity.com/t/build-error-in-2023-1-0a22/904003/2

wicked estuary Dec 8, 2025, 3:24 PM

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deep quest Finally figured it out, turned out to be a UnityEvent with a tuple in it, meanin...

If you want to be helpful for futurue "generations" create a dedicated bug report 😄

#Mysterious build exceptions with no StackTrace