With source generators coming in C# 9, we can look into removing some reflection-based code-generation that we do. This would make Npgsql more compatible with AOT environments, improve startup perf a little and is safer (compile-time checking). Here's where we currently do code generation:

• Type handler code for non-generic writes (e.g. here). Done in Generate non-generic write logic with source generators #3513.
• Array reader delegates (here).
• Composite handling. This could be tricky because the user can map arbitrary .NET CLR types to POCOs at runtime - we may need to leave this as-is.

#3300 tracks making Npgsql friendlier to the linker (big overlap with this).