index: Fix missing case in the comment in NextSyncBlock() #32875

1. 
   HowHsu commented at 10:03 am on July 4, 2025: none

   The comment here overlooked a specific case where the block is the tip of m_chain, fix it.
2. DrahtBot added the label UTXO Db and Indexes on Jul 4, 2025
3. 
   DrahtBot commented at 10:03 am on July 4, 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/32875.

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

4. 
   stickies-v commented at 2:41 pm on July 4, 2025: contributor

   You’re correct that the current docstring is incorrect. I personally don’t find your suggestion very clear either, as the two cases talk about different parts of the return statement.

   An alternative would be to keep the docstring as-is and just make the chaintip case more explicit in code:

   0    const CBlockIndex* pindex = chain.Next(pindex_prev);
   1    if (pindex || pindex_prev == chain.Tip()) {
   2        return pindex;
   3    }
   

    0diff --git a/src/index/base.cpp b/src/index/base.cpp
    1index 8c958ac5f6..506ee73d2e 100644
    2--- a/src/index/base.cpp
    3+++ b/src/index/base.cpp
    4@@ -140,15 +140,12 @@ static const CBlockIndex* NextSyncBlock(const CBlockIndex* pindex_prev, CChain&
    5     }
    6 
    7     const CBlockIndex* pindex = chain.Next(pindex_prev);
    8-    if (pindex) {
    9+    if (pindex || pindex_prev == chain.Tip()) {
   10         return pindex;
   11     }
   12 
   13-    // Two cases goes here:
   14-    // 1. pindex_prev is the tip: chain.FindFork(pindex_pre) returns pindex_prev itself
   15-    // 2. pindex_prev is not in m_chain: since block is not in the chain, return the next
   16-    // block in the chain AFTER the last common ancestor. Caller will be responsible for
   17-    // rewinding back to the common ancestor.
   18+    // If block is not in the chain, return the next block in the chain AFTER the last common ancestor.
   19+    // Caller will be responsible for rewinding back to the common ancestor.
   20     return chain.Next(chain.FindFork(pindex_prev));
   21 }
   22 
   

5. 
   HowHsu commented at 3:15 pm on July 4, 2025: none

   You’re correct that the current docstring is incorrect. I personally don’t find your suggestion very clear either, as the two cases talk about different parts of the return statement.

   An alternative would be to keep the docstring as-is and just make the chaintip case more explicit in code:

   0    const CBlockIndex* pindex = chain.Next(pindex_prev);
   1    if (pindex || pindex_prev == chain.Tip()) {
   2        return pindex;
   3    }
   

   git diff on d6bf3b1

   True, I’ll update it.

6. HowHsu force-pushed on Jul 4, 2025
7. 
   HowHsu commented at 3:41 pm on July 4, 2025: none

   You’re correct that the current docstring is incorrect. I personally don’t find your suggestion very clear either, as the two cases talk about different parts of the return statement.

   An alternative would be to keep the docstring as-is and just make the chaintip case more explicit in code:

   0    const CBlockIndex* pindex = chain.Next(pindex_prev);
   1    if (pindex || pindex_prev == chain.Tip()) {
   2        return pindex;
   3    }
   

   git diff on d6bf3b1

   Hey stickies-v, do you mind me add Suggested-by tag of you?

8. index: handle case where pindex_prev equals chain tip in NextSyncBlock()

   When pindex_prev is the chain tip, return early rather than mixing it
   with the reorg case.
   
   Suggested-by: stickies-v
   Signed-off-by: Hao Xu <hao.xu@linux.dev>

   cf2551883b
9. HowHsu force-pushed on Jul 4, 2025
10. 
    luke-jr commented at 8:57 pm on July 7, 2025: member

    0    CBlockIndex* NextInclRewind(const CBlockIndex* pindex) const
    1    {
    2        if (!Contains(Assert(pindex))) {
    3            pindex = Assert(FindFork(pindex));
    4        }
    5        return (*this)[pindex->nHeight + 1];
    6    }
    

Contributors
HowHsu DrahtBot stickies-v luke-jr

Labels
UTXO Db and Indexes