test: add unit test coverage for the empty leaves path in MerkleComputation #33858

1. 
   frankomosh commented at 0:08 am on November 12, 2025: contributor

   As noted in #32243 (comment), the early return inside MerkleComputation when leaves.size() == 0 was only exercised by fuzz tests.

   The existing merkle_test_empty_block calls BlockMerkleRoot, which uses ComputeMerkleRoot, but does not exercise the TransactionMerklePath → ComputeMerklePath → MerkleComputation code path.

   Coverage before adding test:

   Coverage after adding test:

2. test: exercise TransactionMerklePath with empty block; targets the MerkleComputation empty-leaves path that was only reached by fuzz tests ffcae82a68
3. DrahtBot added the label Tests on Nov 12, 2025
4. 
   DrahtBot commented at 0:08 am on November 12, 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/33858.

   Reviews

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   Type	Reviewers
   ACK	kevkevinpal, brunoerg, maflcko, sedited

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5. 
   maflcko commented at 8:14 am on November 12, 2025: member

   Coverage before adding test:

   Coverage after adding test:

   I don’t think those links work. Also, this is redundant to the corecheck result anyway?

6. 
   frankomosh commented at 11:16 am on November 12, 2025: contributor

   I don’t think those links work.

   I’m not sure why they didn’t render correctly here. [Edit: I think it renders now]

   Also, this is redundant to the corecheck result anyway?

   I included them mainly to visually show % increase, but you’re right that they may be redundant. (also, I think you have been against adding tests without showing any proof of coverage)

7. 
   kevkevinpal commented at 3:07 pm on November 12, 2025: contributor

   ACK ffcae82

   According to corecheck it looks like there was an increase in coverage https://corecheck.dev/bitcoin/bitcoin/pulls/33858

8. in src/test/merkle_tests.cpp:160 in ffcae82a68

   153@@ -154,6 +154,11 @@ BOOST_AUTO_TEST_CASE(merkle_test_empty_block)
   154 
   155     BOOST_CHECK_EQUAL(root.IsNull(), true);
   156     BOOST_CHECK_EQUAL(mutated, false);
   157+
   158+    // Verify TransactionMerklePath handles empty block correctly
   159+    // This tests the early-return path in MerkleComputation
   160+    std::vector<uint256> merkle_path = TransactionMerklePath(block, 0);
   

   ---

   ---

   

   brunoerg commented at 7:24 pm on November 20, 2025:

   nit:

   0    std::vector<uint256> merkle_path = TransactionMerklePath(block, /*position=*/0);
   

   ---

   

   frankomosh commented at 7:17 pm on November 24, 2025:

   Thanks for suggestion. Can we keep it this way for now?
9. brunoerg approved
10. 
    brunoerg commented at 7:28 pm on November 20, 2025: contributor

    code review ACK ffcae82a68104c1992964b26c592b62cbca391bf

    It’s just a simple test addition to exercise MerkleComputation with an empty vector of leaves, it’s ok. Note that it just checks the path is empty which is fine since there is a proposal to remove the unused pmutated and proot (https://github.com/bitcoin/bitcoin/pull/33805).

11. 
    maflcko commented at 10:26 am on November 21, 2025: member

    lgtm ACK ffcae82a68104c1992964b26c592b62cbca391bf
12. sedited approved
13. 
    sedited commented at 1:35 pm on December 4, 2025: contributor

    ACK ffcae82a68104c1992964b26c592b62cbca391bf

    rfm?

14. 
    frankomosh commented at 12:22 pm on December 5, 2025: contributor

    rfm?

    I think it is

15. fanquake merged this on Dec 5, 2025
16. fanquake closed this on Dec 5, 2025

    ---

17. frankomosh deleted the branch on Dec 6, 2025

Contributors
frankomosh DrahtBot maflcko kevkevinpal brunoerg sedited

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