Update the KotlinUnsafeCastOperatorFilter for Kotlin 1.6.0

[poseidon-mysugr]

The Kotlin 1.6.0 compiler changed how "unsafe casts" are compiled. Consider the following Kotlin class:

class Cast {
    fun cast(any: Any?): String {
        return any as String
    }
}

The Kotlin 1.5.32 compiler compiles the cast function to

  public final java.lang.String cast(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/String;
    flags: (0x0011) ACC_PUBLIC, ACC_FINAL
    Code:
      stack=3, locals=2, args_size=2
         0: aload_1
         1: ifnonnull     14
         4: new           #16                 // class java/lang/NullPointerException
         7: dup
         8: ldc           #18                 // String null cannot be cast to non-null type kotlin.String
        10: invokespecial #21                 // Method java/lang/NullPointerException."<init>":(Ljava/lang/String;)V
        13: athrow
        14: aload_1
        15: checkcast     #23                 // class java/lang/String
        18: areturn
      StackMapTable: number_of_entries = 1
        frame_type = 14 /* same */
      LineNumberTable:
        line 5: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      19     0  this   Lcom/mysugr/Cast;
            0      19     1   any   Ljava/lang/Object;
    RuntimeInvisibleAnnotations:
      0: #13()
        org.jetbrains.annotations.NotNull
    RuntimeInvisibleParameterAnnotations:
      parameter 0:
        0: #14()
          org.jetbrains.annotations.Nullable

while the Kotlin 1.6.0 compiler produces:

  public final java.lang.String cast(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/String;
    flags: (0x0011) ACC_PUBLIC, ACC_FINAL
    Code:
      stack=3, locals=2, args_size=2
         0: aload_1
         1: dup
         2: ifnonnull     16
         5: pop
         6: new           #16                 // class java/lang/NullPointerException
         9: dup
        10: ldc           #18                 // String null cannot be cast to non-null type kotlin.String
        12: invokespecial #21                 // Method java/lang/NullPointerException."<init>":(Ljava/lang/String;)V
        15: athrow
        16: checkcast     #23                 // class java/lang/String
        19: areturn
      StackMapTable: number_of_entries = 1
        frame_type = 80 /* same_locals_1_stack_item */
          stack = [ class java/lang/Object ]
      LineNumberTable:
        line 5: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      20     0  this   Lcom/mysugr/Cast;
            0      20     1   any   Ljava/lang/Object;
    RuntimeInvisibleAnnotations:
      0: #13()
        org.jetbrains.annotations.NotNull
    RuntimeInvisibleParameterAnnotations:
      parameter 0:
        0: #14()
          org.jetbrains.annotations.Nullable

The 1.6.0 compiler duplicates the variable that's being casted before checking whether it's null, and pops the extra copy from the stack in case it is null; previous compilers instead loaded the variable a second time if it wasn't null.

This change makes the KotlinUnsafeCastOperatorFilter not detect the unsafe cast anymore because of the extra POP instruction; allowing this instruction to be there but not requiring it makes the filter compatible with both variants.

[Godin]

For the record this relates to the following change in Kotlin compiler - JetBrains/kotlin@041773f#diff-c479e51c961b3189024716a2e505117e50c2f05b630be1ea40ec70304a34f16aR250-R331

---

Change in KotlinUnsafeCastOperatorFilter looks good to me 👍 , however requires addition of test to corresponding KotlinUnsafeCastOperatorFilterTest, and update of changelog.

Unfortunately I can't push these little missing things directly into your branch, because seems that your branch is in org-repository and GitHub doesn't allow to enable "Allow edits from maintainers" for such - https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork

So finalized this in #1266

Thank you for your contribution ❤️

[poseidon-mysugr]

Thanks a lot, @Godin!