Kotlin. error: Event fields must be declared as public non-final.

• I have searched existing issues and this is not a duplicate

Version

    implementation "com.facebook.soloader:soloader:0.6.0"

    // ext.litho_version = '0.32.0'
    implementation "com.facebook.litho:litho-core:$litho_version"
    implementation "com.facebook.litho:litho-widget:$litho_version"
    kapt "com.facebook.litho:litho-processor:$litho_version"
    implementation "com.facebook.litho:litho-fresco:$litho_version"
    implementation "com.facebook.litho:litho-sections-core:$litho_version"
    implementation "com.facebook.litho:litho-sections-widget:$litho_version"
    compileOnly "com.facebook.litho:litho-sections-annotations:$litho_version"
    kapt "com.facebook.litho:litho-sections-processor:$litho_version"

Issues and Steps to Reproduce

Create a Kotlin Custom Event

import com.facebook.litho.annotations.Event

@Event
class StorefrontRowMinimizedEvent(
    var storefrontRowId: String = ""
)

Use this event in a Spec

@LayoutSpec(events = [StorefrontRowMinimizedEvent::class])
object StorefrontItemComponentSpec {
    private const val TAG : String = "StorefrontItem"

You will see error

Event fields must be declared as public non-final.
    private java.lang.String storefrontRowId;
                                         ^

This is how it was compiled in Java

import java.lang.System;

@com.facebook.litho.annotations.Event()
@kotlin.Metadata(...)
public final class StorefrontRowMinimizedEvent {
    @org.jetbrains.annotations.NotNull()
    private java.lang.String storefrontRowId;
    
    @org.jetbrains.annotations.NotNull()
    public final java.lang.String getStorefrontRowId() {
        return null;
    }
    
    public final void setStorefrontRowId(@org.jetbrains.annotations.NotNull()
    java.lang.String p0) {
    }
    
    public StorefrontRowMinimizedEvent(@org.jetbrains.annotations.NotNull()
    java.lang.String storefrontRowId) {
        super();
    }
    
    public StorefrontRowMinimizedEvent() {
        super();
    }
}

Special emphasis on

    @org.jetbrains.annotations.NotNull()
    private java.lang.String storefrontRowId;

Expected Behavior

This should have been public because, in Kotlin, everything is public by default. Also, even if you mark it public it’s still private 😢. The output should be something like this:

    @org.jetbrains.annotations.NotNull()
    public java.lang.String storefrontRowId;

Workaround for now. Use Java

import com.facebook.litho.annotations.Event;

@Event
public class StorefrontItemSelectedEvent {
    public String StorefrontItemId;
}

Link to Code

Intentionally not added because this is fairly easy to reproduce.

Please show some code we can use to reproduce this issue. Consider using PlaygroundComponentSpec to provide a small example of the issue

[pavlospt]

It can not be public because Kotlin adds setters/getters for the fields and keeps it private. The real fix here should be that the AP will check if this is a Kotlin class in order to use the appropriate getter, when accessing that field. @passy @pasqualeanatriello I could probably have a look at it if needed!

[colriot]

Hi @NishcheyBhutani . Issue is still open, but the open-source work has already been done by Pavlos. The blocker is in the internal integration at FB.