flatten module order error

[luozejiaqun]

Fixes #1998

[arnaudgiuliani]

I don't see other feedback on that. Let's reopen if needed in 4.2

[luozejiaqun]

@Test
fun test_flatten_common() {
    val m1 = module { }
    val m2 = module { }
    val m3 = module { includes(m1, m2) }
    val modules = m3 + m2

    assertSetEqualsInOrder(flatten(modules), setOf(m3, m1, m2))
}

the test can illustrate the issue clearly. Without the fix, the result will be m3, m2, m1, which is obviously wrong.

[luozejiaqun]

Let me explain it in a more practical case:

interface Cryptographer {
  fun encrypt()
  fun decrypt()
}

// implement in common
class SoftwareImplement : Cryptographer

expect val platformCryptographerModule: Module

val cryptographerModule = module {
  singleOf(::SoftwareImplement) binds Cryptographer::class
}

// implement in android & iOS
class HarewareAccelerator : Cryptographer

// in androidMain & iOSMain
actual val platformCryptographerModule = module {
  singleOf(::HarewareAccelerator) binds Cryptographer::class
}

val appModule = module {
  includes(
    cryptographerModule,
    platformCryptographerModule,
  )
}

// without the fix, the result will be
koin.get<Cryptographer>() is SoftwareImplement

Of course, if I know the issue, or I just prefer the following usage:

val cryptographerModule = module {
  singleOf(::SoftwareImplement) binds Cryptographer::class
  includes(platformCryptographerModule)
}

val appModule = module {
  includes(
    cryptographerModule,
  )
}

// no problem
koin.get<Cryptographer>() is HarewareAccelerator

This can cause an issue only when we include two modules, and they contain some overrided parts. This maybe the reason why there is no other feedback.