FA-75509 / Text diff and three-way merge / Member archive

Patience diff anchors: lines repeated in the new side become anchors · case 04

A line duplicated in the new file anchors to its last copy and misaligns the diff.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Candidates are lines occurring exactly once in the old side and exactly once in the new side, as (old index, new index) pairs in old order. Keep the longest chain with increasing new index, found with patience piles (bisect on pile tops by new index, back pointers to the previous pile top) and reconstructed from the top of the last pile. Return the anchor pairs.

Why this case matters

Patience diff anchors on unique lines to produce readable diffs of code with many repeated braces and blank lines.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
duplicated in new side are not anchors	`[[0, 1], [1, 2], [2, 3]]`	`[[0, 1], [2, 3]]`	Failed

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