validation: invalid block handling followups #32843

1. 
   mzumsande commented at 10:10 pm on June 30, 2025: contributor

   Some follow-ups from #31405:

   • avoid duplicate recalculation of failure flags and m_best_header in InvalidateBlock(), which already does the accounting for these quantities while disconnecting blocks, so recalcuation is not needed in the final InvalidChainFound call (https://github.com/bitcoin/bitcoin/pull/31405#discussion_r2138368309)
   • make it clearer that all block indexes with a CBlockIndexWorkComparator score at least as good as the tip (and no others) are expected in setBlockIndexCandidates. People think of nChainWork when the term work is used and not of the (slightly arbitrary) CBlockIndexWorkComparator tiebreaker rules, which makes the current documentation imprecise ( #31405 (review) )
   • add a comment that nChainWork, not CBlockIndexWorkComparator is used for m_best_header (https://github.com/bitcoin/bitcoin/pull/31405#discussion_r2138368441)
2. validation: Don't repeat work in InvalidateBlock

   In InvalidateBlock, both the block failure flags
   and m_best_header are kept up to date with each block
   that is disconnected, so it's not necessary to recalculate
   them at the end of this function.

   30b190eeba
3. DrahtBot added the label Validation on Jun 30, 2025
4. 
   DrahtBot commented at 10:10 pm on June 30, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/32843.

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   See the guideline for information on the review process. A summary of reviews will appear here.

   Conflicts

   Reviewers, this pull request conflicts with the following ones:

   • #30214 (refactor: Improve assumeutxo state representation by ryanofsky)

   If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

5. doc: Improve doc for candidate blocks

   It is not true in general that all blocks with the same work
   (as defined via nChainWork) as the tip are candidates expected to be in
   setBlockIndexCandidates - only ones with a better tiebreak than the tip.
   Make that clear in various spots.
   
   Also explain that we don't use CBlockIndexWorkComparator tiebreak rules
   for m_best_header.

   e32e72039f
6. mzumsande force-pushed on Jun 30, 2025

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