K2 is too strict with expect/actual And makes thi...

# k2-adopters

[andylamax]

K2 is too strict with expect/actual

And makes this feature hard to use with type aliasing. Below is the explainer

Given the following sources

• src/commonMain/Promise.kt

expect interface Promise<out T>

• src/jvmMain/Promise.kt

@file:Suppress(
    "ACTUAL_WITHOUT_EXPECT",
    "ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE"
) 

actual typealias Promise<T> = java.util.concurrent.CompletionStage<T>

Results are as follows
a) Without any suppresses, the compilation fails with

• 'actual typealias Promise<T> = CompletionStage<T>' has no corresponding expected declaration
• The following declaration is incompatible because declaration-site variances of type parameters are different
On both kotlin K1 (1.9.21) and K2 (2.0.0-Beta1,2.0.0-Beta2)


b) With @Suppress("ACTUAL_WITHOUT_EXPECT")
The program compiles file on K1 (1.9.21)
but fails on K2 (2.0.0-Beta1,2.0.0-Beta2)
• Expect declaration Promise is incompatible with actual Promise because declaration-site variances of type parameters are different
c) With @Suppress("ACTUAL_WITHOUT_EXPECT","ACTUAL_TYPE_ALIAS_TO_CLASS_WITH_DECLARATION_SITE_VARIANCE")
Results are similar to (b), its like the former suppress directive has no effect at all


Now I know the kotlin team doesn't really investigate code with suppresses, but how should we approach this currently?? I can't seem to be able to provide an actual type alias for this.

Also, is there a current issue for this?? Or should I file a ticket??

[dmitriy.novozhilov]

cc @bobko

[Edoardo Luppi]

There is already an issue for this, which I opened some months ago.
https://youtrack.jetbrains.com/issue/KT-61043
Which is also related to https://youtrack.jetbrains.com/issue/KT-21846