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kotlinlang

Is it possible to check `is` and `as` expressions?
Is there `DeclarationChecker` analog for such checks?

If you're asking about FIR there's `ExpressionCheckers`

FIR is not directly related to IR
FIR (aka K2) is a new compiler frontend, which works before backend IR stage
If you want to report diagnostics on `is` and `as` from compiler plugin then there are two options:
1. Create `DeclarationChecker` in your plugin for old frontend (it's the one with PSI and BindingContext) and manually traverse body with some visitor
2. Write frontend part of your plugin for FIR and create your own `FirTypeOperatorCallChecker` (it will be called only for `is` and `as` expression)
First option can be used in production plugin right now (because current frontend is stable)
Second option will require to completely rewrite fronted part of your plugin, but it provide more powerful and nice API, so it's great option for some research

And if you choose first option you will still require to rewrite your plugin to FIR when it becomes stable and default