Fix #2591

[tomaka]

Fix #2591

This PR fixes the internal logic of parachain.rs and, importantly, clarifies it.

The code was doing some very wrong things with the finalized_parahead variable. This variable might be equal to a very old block (typically the genesis block), yet the code would use it as a fallback in various situations.

This would lead to the SyncService reporting that the parent of a recent block was equal to the genesis block (in theory could have been another block than genesis, but in practice the genesis block). As a consequence, the RuntimeService would download the runtime of the genesis block and think that the recent block was using the same, since it is a child and didn't indicate that a runtime upgrade occurred.

#2591 was fixed by adding a simple if block that clears all active subscriptions once a finalized parahead is known, and two other if blocks that prevent notifications from being emitted before the finalized parahead is known. This makes me think that this logic got accidentally removed in a refactoring.

[mergify]

Automatically approving tomaka's pull requests. This auto-approval will be removed once more maintainers are active.

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

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 Delta Bytes │ Item
─────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
      +13366 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h31e4c97e9521579e
      -13044 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h90130d2061e5f423
        -471 ┊ core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut::hf72ecf625d97af24
        -438 ┊ core::ptr::drop_in_place<core::future::from_generator::GenFuture<smoldot_light_base::sync_service::parachain::start_parachain<smoldot_light_wasm::platform::Platform>::{{closure}}>>::h7678abfe060201b0
        +438 ┊ core::ptr::drop_in_place<core::future::from_generator::GenFuture<smoldot_light_base::sync_service::parachain::start_parachain<smoldot_light_wasm::platform::Platform>::{{closure}}>>::h8d686787dff410aa
        +402 ┊ core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut::hfa05bfd79530e126
        -392 ┊ itertools::Itertools::join::h0f2b610b81ce4d3c
        +392 ┊ itertools::Itertools::join::heb0697138391f5d0
        +376 ┊ <futures_util::future::poll_fn::PollFn<F> as core::future::future::Future>::poll::h7ef56618e416d103
        -376 ┊ <futures_util::future::poll_fn::PollFn<F> as core::future::future::Future>::poll::had0db3ab4dd3211b
        -270 ┊ <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::h26f7ee3d152c2785
        +270 ┊ <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::hc05e7ecabc9fad11
        -259 ┊ <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::h211b9525b15f1bb1
        +259 ┊ <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::h977c5f9964d931f0
        +241 ┊ core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once::h04e45e1c3a206db1
        -241 ┊ core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once::ha94b8192050fe86c
        -240 ┊ <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold::hc499c69c11883d14
        +240 ┊ <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold::hd0ba7c98651323ec
        +233 ┊ <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::h395dd64765d73847
        -233 ┊ <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::hc52f39fd79e7a3f5
        +101 ┊ ... and 88 more.
        +756 ┊ Σ [108 Total Rows]