[InitializeOnLoad] called during asset import since 2018?

I'm investigating a lot of different user reported issues for my plugin Bolt that seem to happen during import and appear to start after Unity 2018.x.

I do my initialization code uising [InitializeOnLoad] attributes. From my understanding, this attribute calls static type initializers on assembly reload, that is:

• When the editor starts
• When entering play mode
• When the project recompiles
• After an import of new DLLs

I think all of my recent issues are coming from that last item. From the symptoms, it seems that importing multiple DLLs causes multiple assembly reloads after each DLL instead of a single assembly reload at the end.

This is a breaking change for my plugin (and I'm guessing many others!) because I can't guarantee that the my initialization code will work unless all assemblies are properly loaded.

So my questions are:

• Was this change in the behaviour of assembly reload documented anywhere?
• Is there a way of detecting that the Unity editor is currently importing assets?

If I could answer that second one, I could just skip initialization during asset import and wait for an actual full reload at the end.

 

Is it what you are looking for : https://docs.unity3d.com/ScriptReference/EditorApplication-isUpdating.html?

 

Ah! This does seem to do the trick, but it also returns true after all DLLs have been loaded (or when the last DLL is loaded). So if I skip my initialization while isUpdating returns true, it won't initialize after a recompile or an import. :/

 

I take that back. EditorApplication.isUpdating sometimes returns false during asset import when opening the project, so it's entirely unreliable for me at the moment.

Was there any change in the import/assembly load behaviour since 2018? A lot of my users are reporting issues that seem to stem from there.