DRAFT: fix some diff ordering issues#89
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- Extract the LCS-driven walk that was inlined inside diff_block_lists (and duplicated inside diff_list_nodes) into a single generic _merge_with_lcs that returns an ordered (op, element) stream. - Generalize _pair_adjacent_changes to take pair / wrap_deletion / wrap_insertion callbacks so it can fold the same stream for both Pandoc blocks and list items, instead of operating on already-wrapped Divs. - Add _pair_blocks helper carrying the per-pair recursion strategy (lists / BlockQuotes / LineBlocks) used by diff_block_lists. - Reduce diff_list_nodes from a hand-written merge+pair loop to a thin call into the shared helpers.
ie, a before with: - <unchanged node that is duplicated elsewhere> - <altered node - old> and after with: - <unchanged node that is duplicated elsewhere> - <altered node - new> would sometimes result in: - <Added: <changed node - new>> - <unchanged node that is duplicated elsewhere> - <Removed: <changed node - old>> ...instead of - <unchanged node that is duplicated elsewhere> - <Removed: <changed node - old>> - <Added: <changed node - new>> This would make it seem that the new version moved the unchanged node after the altered node, when it didn't. Additionally, it prevented the altered node from being detected as a substitution.
diff_block_lists and diff_list_nodes previously checked LCS membership via set lookup, then assumed two pointers each "in the LCS" must be at the same LCS position. With duplicate nodes (or earlier pointer drift) the two pointers could be at different LCS elements; pairing them advanced both ptrs across mismatched positions and produced merged output where deletions and insertions were no longer adjacent for _pair_adjacent_changes to fold into substitutions. Drive the merge from the LCS list in order: at each LCS element drain non-LCS blocks from 'before' as deletions and from 'after' as insertions, then take the LCS block. Same shape applied to diff_list_nodes. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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