I've been trying the latest merged changes that add support for external errors on Android, and I've found that UniFFI is not correctly doing the *Error to *Exception rename when the external error is being used inside another error type:

// This error is defined in crate-a

#[derive(uniffi::Error)]
pub enum TestError {
    BadThingsHappened(String),
    ErrorFromCrateB(crate_b::CrateBError),
}

// This error is defined in crate-b
#[derive(uniffi::Error)]
pub enum CrateBError {
    CrateBScrewedUp(u64),
}

If I check the generated bindings, I can see that the rename is done correctly in crate_b.kt:

sealed class CrateBException: kotlin.Exception() {
...
}

But when it gets imported in crate_a.kt, the rename doesn't happen:

import uniffi.crate_b.CrateBError    // <!--- Compile error here

sealed class TestException: kotlin.Exception() {
    class BadThingsHappened(
        val v1: kotlin.String
        ) : TestException() { ... }
    
    class ErrorFromCrateB(
        val v1: CrateBError    // <!--- Compile error here
        ) : TestException() { ...  }

If I manually rename the CrateBError to CrateBException in the file everything works correctly, so this seems to only be a bug in the template generation. Let me know if you need more info, I have a repro here if it's helpful: https://github.com/dani-garcia/uniffi-android-error-repro