Kotlin 1.4 -Xuse-ir marks lateinit fields as Nullable forcing NullAway to flag calls as unsafe

It's more of a heads-up issue for now.

We're trying Kotlin 1.4 with -Xuse-ir to use JetPack Compose, however we found that it generates different bytecode for lateinit backing fields.

Kotlin code:

internal lateinit var textView: TextView

-Xuse-ir produces following bytecode:

public android.widget.TextView textView;
descriptor: Landroid/widget/TextView;
flags: (0x0001) ACC_PUBLIC
RuntimeInvisibleAnnotations:
    0: #13()
    org.jetbrains.annotations.Nullable

Regular compiler backend produces following:

public android.widget.TextView textView;
descriptor: Landroid/widget/TextView;
flags: (0x0001) ACC_PUBLIC
RuntimeInvisibleAnnotations:
    0: #7()
    org.jetbrains.annotations.NotNull

As you can see, regular backend marks the field as @NotNull, while ir backend marks it as @Nullable.

Which in turn breaks NullAway, it starts flagging Java calls to lateinit fields as unsafe.

For now, I think it's an issue for Kotlin team to figure out, because it's a breakage of public API, but technically, they're not wrong marking lateinit as Nullable…

Potential solution in NullAway would be to parse Kotlin metadata annotations to figure out if it's a lateinit field, but that sounds like a Kotlin specific solution which is not great.

Upstream Kotlin issue: https://youtrack.jetbrains.com/issue/KT-43177

Start with the Kotlin example and compare the regular-backend and -Xuse-ir bytecode shown in the issue, then review upstream Kotlin issue KT-43177. Check how NullAway handles the generated @Nullable annotation on lateinit fields. The issue does not define a NullAway-side change or a clear completion condition.