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refactor: Drop util::Result operator=

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`util::Result` objects are aggregates that can hold multiple fields with
different information. Currently Result objects can only hold a success value
of an arbitrary type or a single bilingual_str error message. In followup PR
https://github.com/bitcoin/bitcoin/pull/25722, Result objects may be able to
hold both success and failure values of different types, plus error and warning
messages.

Having a Result::operator= assignment operator that completely erases all
existing Result information before assigning new information is potentially
dangerous in this case. For example, code that looks like it is assigning a
warning value could erase previously-assigned success or failure values.
Conversely, code that looks like it is just assigning a success or failure
value could erase previously assigned error and warning messages.

To prevent potential bugs like this, disable Result::operator= assignment
operator.

It is possible in the future we may want to re-enable operator= in limited
cases (such as when implicit conversions are not used) or add a Replace() or
Reset() method that mimicks default operator= behavior. Followup PR
https://github.com/bitcoin/bitcoin/pull/25722 also adds a Result::Update()
method providing another way to update an existing Result object.

Co-authored-by: stickies-v <stickies-v@protonmail.com>
This commit is contained in:
Ryan Ofsky
2022-09-15 11:15:06 -04:00
parent 2eff198f49
commit 834f65e824
7 changed files with 40 additions and 28 deletions
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13
src/validation.cpp
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@@ -946,8 +946,9 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
maybe_rbf_limits.descendant_size_vbytes += conflict->GetSizeWithDescendants();
}
auto ancestors{m_pool.CalculateMemPoolAncestors(*entry, maybe_rbf_limits)};
if (!ancestors) {
if (auto ancestors{m_pool.CalculateMemPoolAncestors(*entry, maybe_rbf_limits)}) {
ws.m_ancestors = std::move(*ancestors);
} else {
// If CalculateMemPoolAncestors fails second time, we want the original error string.
// Contracting/payment channels CPFP carve-out:
// If the new transaction is relatively small (up to 40k weight)
@@ -970,11 +971,13 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
if (ws.m_vsize > EXTRA_DESCENDANT_TX_SIZE_LIMIT) {
return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "too-long-mempool-chain", error_message);
}
ancestors = m_pool.CalculateMemPoolAncestors(*entry, cpfp_carve_out_limits);
if (!ancestors) return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "too-long-mempool-chain", error_message);
if (auto ancestors_retry{m_pool.CalculateMemPoolAncestors(*entry, cpfp_carve_out_limits)}) {
ws.m_ancestors = std::move(*ancestors_retry);
} else {
return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "too-long-mempool-chain", error_message);
}
}
ws.m_ancestors = *ancestors;
// Even though just checking direct mempool parents for inheritance would be sufficient, we
// check using the full ancestor set here because it's more convenient to use what we have
// already calculated.