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<@U9APPH5AA> Generally, if you're looking for some compiler part that reports error/warning, then it's quite easy to find it:

- Start with class `org.jetbrains.kotlin.diagnostics.Errors`, and look for that particular diagnostic (in your case, it's a `CONFLICITNG_OVERLOADS`).

- Then, find its usages and check where it is reported. You're looking for calls to `BindingTrace.report(SOME_DIAGNOSTIC_FACTORY_FROM_ERRORS.on(...))`. 
Again, in your case there are some not-so-relevant usages, e.g. in `LocalRedeclarationChecker`, and the main one is in the `OverloadResolved.kt`, which is the answer to your question.