diff: walk LCS as ordered list, not set, to fix block ordering#94
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pmolodo wants to merge 2 commits into
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diff: walk LCS as ordered list, not set, to fix block ordering#94pmolodo wants to merge 2 commits into
pmolodo wants to merge 2 commits into
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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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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.