Room recently moved some of its APIs and source from Java to Kotlin and int def enforcement seems to have been lost with the move.

Given the IntDef in Room OnConflictStrategy, wrong usage of it in Kotlin gives no warning:

@Dao
interface MyDao {
    @Insert(onConflict = 20)  // Error should be here due to bad constant used.
    fun insert(e: MyEntity)
}

the enforcement is also lost in Java sources:

@Dao
public interface MyJavaDao {
    @Insert(onConflict = 20) // Error should be here due to bad constant used.
    void insert(MyEntity e);
}

However, if I make a new @IntDef along with an annotation in Java, the enforcement works fine.

@IntDef({MyIntDef.VALUE1, MyIntDef.VALUE2})
public @interface MyIntDef {
    int VALUE1 = 1;
    int VALUE2 = 2;
}

public @interface MyJavaAnnotation {
    @MyIntDef int value();
}

@MyJavaAnnotation(20) // Fails with 'Must be one of: MyIntDef.VALUE1, MyIntDef.VALUE2'
fun aFunction() {
}

Let me know if you need more information!