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Merge bitcoin/bitcoin#34006: Add util::Expected (std::expected)

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faa23738fc refactor: Enable clang-tidy bugprone-unused-return-value (MarcoFalke)
fa114be27b Add util::Expected (std::expected) (MarcoFalke)

Pull request description:

  Some low-level code could benefit from being able to use `std::expected` from C++23:

  * Currently, some code is using `std::optional<E>` to denote an optional error. This is fine, but a bit confusing, because `std::optional` is normally used for values, not errors. Using `std::expected<void, E>` is clearer.
  * Currently, some code is using `std::variant<V, E>` to denote either a value or an error. This is fine, but a bit verbose, because `std::variant` requires a visitor or get_if/holds_alternative instead of a simple call of the `operator bool` for `std::expected`.

  In theory, `util::Result` could be taught to behave similar to `std::expected` (see https://github.com/bitcoin/bitcoin/pull/34005). However, it is unclear if this is the right approach:

  * `util::Result` is mostly meant for higher level code, where errors come with translated error messages.
  * `std::expected` is mostly meant for lower level code, where errors could be an enum, or any other type.
  * https://github.com/bitcoin/bitcoin/pull/25665 aims to minimize the memory footprint of the error by wrapping it in a unique_ptr internally. `std::expected` requires the value and error to be "nested within it" (https://cplusplus.github.io/LWG/issue4141). So from a memory-layout perspective, the two are not compatible.
  * `std::expected` also comes with `std::unexpected`, which also does not map cleanly to `util::Result`.

  So just add a minimal drop-in port of `std::expected`.

ACKs for top commit:
  romanz:
    tACK faa23738fc
  sedited:
    Re-ACK faa23738fc
  hodlinator:
    ACK faa23738fc
  rkrux:
    light Code Review ACK faa23738fc
  ryanofsky:
    Code review ACK faa23738fc, only adding `value_or` implementation and `CheckedReturnTypes` clang-tidy commit since last review.
  stickies-v:
    ACK faa23738fc

Tree-SHA512: fdbd0f6bf439738ffe6a68da5522f1051537f8df9c308eb90bef6bd2e06931d79f1c5da22d5500765e9cb1d801d5be39e11e10d47c9659fec1a8c8804cb7c872
This commit is contained in:
Ryan Ofsky
2025-12-08 19:50:49 -05:00
parent 77248e8496 faa23738fc
commit d5c8199b79
15 changed files with 191 additions and 20 deletions
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16
src/net_processing.cpp
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@@ -530,7 +530,7 @@ public:
/** Implement PeerManager */
void StartScheduledTasks(CScheduler& scheduler) override;
void CheckForStaleTipAndEvictPeers() override;
std::optional<std::string> FetchBlock(NodeId peer_id, const CBlockIndex& block_index) override
util::Expected<void, std::string> FetchBlock(NodeId peer_id, const CBlockIndex& block_index) override
EXCLUSIVE_LOCKS_REQUIRED(!m_peer_mutex);
bool GetNodeStateStats(NodeId nodeid, CNodeStateStats& stats) const override EXCLUSIVE_LOCKS_REQUIRED(!m_peer_mutex);
std::vector<node::TxOrphanage::OrphanInfo> GetOrphanTransactions() override EXCLUSIVE_LOCKS_REQUIRED(!m_tx_download_mutex);
@@ -1844,16 +1844,16 @@ bool PeerManagerImpl::BlockRequestAllowed(const CBlockIndex* pindex)
(GetBlockProofEquivalentTime(*m_chainman.m_best_header, *pindex, *m_chainman.m_best_header, m_chainparams.GetConsensus()) < STALE_RELAY_AGE_LIMIT);
}
std::optional<std::string> PeerManagerImpl::FetchBlock(NodeId peer_id, const CBlockIndex& block_index)
util::Expected<void, std::string> PeerManagerImpl::FetchBlock(NodeId peer_id, const CBlockIndex& block_index)
{
if (m_chainman.m_blockman.LoadingBlocks()) return "Loading blocks ...";
if (m_chainman.m_blockman.LoadingBlocks()) return util::Unexpected{"Loading blocks ..."};
// Ensure this peer exists and hasn't been disconnected
PeerRef peer = GetPeerRef(peer_id);
if (peer == nullptr) return "Peer does not exist";
if (peer == nullptr) return util::Unexpected{"Peer does not exist"};
// Ignore pre-segwit peers
if (!CanServeWitnesses(*peer)) return "Pre-SegWit peer";
if (!CanServeWitnesses(*peer)) return util::Unexpected{"Pre-SegWit peer"};
LOCK(cs_main);
@@ -1861,7 +1861,7 @@ std::optional<std::string> PeerManagerImpl::FetchBlock(NodeId peer_id, const CBl
RemoveBlockRequest(block_index.GetBlockHash(), std::nullopt);
// Mark block as in-flight
if (!BlockRequested(peer_id, block_index)) return "Already requested from this peer";
if (!BlockRequested(peer_id, block_index)) return util::Unexpected{"Already requested from this peer"};
// Construct message to request the block
const uint256& hash{block_index.GetBlockHash()};
@@ -1873,11 +1873,11 @@ std::optional<std::string> PeerManagerImpl::FetchBlock(NodeId peer_id, const CBl
return true;
});
if (!success) return "Peer not fully connected";
if (!success) return util::Unexpected{"Peer not fully connected"};
LogDebug(BCLog::NET, "Requesting block %s from peer=%d\n",
hash.ToString(), peer_id);
return std::nullopt;
return {};
}
std::unique_ptr<PeerManager> PeerManager::make(CConnman& connman, AddrMan& addrman,