Fix IllegalAccessException reading non-public PreferenceKey/EnvironmentKey (#243)

[vincentborko]

Motivation

A custom PreferenceKey or EnvironmentKey declared private or fileprivate crashes the first time its value is read. On Android the key transpiles to a package-private Kotlin class, and reading its companion object via Kotlin reflection throws:

java.lang.IllegalAccessException: class kotlin.reflect.jvm.internal.KClassImpl$Data
cannot access a member of class skip.ui.<Key> with modifiers "public static final"

Root cause

PreferenceKey.swift and EnvironmentValues.swift read the companion via kotlin.reflect.full.companionObjectInstance:

• Preference.init(key:) — key.companionObjectInstance as! PreferenceKeyCompanion<Value>
• View.onPreferenceChange(_:perform:) — key.companionObjectInstance as PreferenceKeyCompanion<V>
• EnvironmentValues.valueCompositionLocal(key:) — key.companionObjectInstance as EnvironmentKeyCompanion<*>

The synthesized companion INSTANCE field is public static final, but the enclosing key class is package-private when the Swift type is private/fileprivate. Kotlin's companionObjectInstance reads that field without calling isAccessible = true, so the JVM access check fails with IllegalAccessException.

Fix

Introduce a small companionInstance(ofType:) helper that resolves the companion via Java reflection with field.isAccessible = true, and route the three call sites through it:

internal fun companionInstance(ofType: KClass<*>): Any? {
    val name = ofType.companionObject?.simpleName ?: "Companion"
    val field = ofType.java.getDeclaredField(name)
    field.isAccessible = true
    return field.get(null)
}

This is the minimal root-level fix — it removes the one missing isAccessible = true rather than forcing every custom key to be public.

Testing

The regression test was previously worked around in 3a7de72 ("Make test PreferenceKey implementation public, working around #243") by making the test EnvironmentKey and its accessor public. This PR reverts that to private/fileprivate, restoring testCustomEnvironmentValue as a genuine reproduction.

• Before the fix (test key private): testCustomEnvironmentValue$SkipUI fails on Robolectric with the IllegalAccessException above — JUNIT ... PASSED 0 FAILED 1.
• After the fix: JUNIT ... PASSED 1 FAILED 0.

Verified with the real Skip SDK via swift test (Robolectric): transpiles, compileDebugKotlin succeeds, and testCustomEnvironmentValue passes with the test key private.

Related

#310 reports what looks like the same root cause surfacing as a null cannot be cast to non-null type ...PreferenceKeyCompanion NPE (a non-public @AppStorage/preference key whose companion reflection fails). This change should resolve it too, though only #243 was reproduced here.

Fixes #243