FA-75404 / Text diff and three-way merge / Member archive

Unified hunk builder: leading context is measured from the last change of a group · case 04

A hunk that groups several changes starts after its first change, losing lines and misnumbering the header.

Member previewVariant 4 · 3 implementations · 11 checks per implementation

Case contract

Given a full edit script ([tag, line], tags " ", "-", "+") and a context width C, group changes whose separating equal lines number at most 2C, extend each group by up to C lines on both sides, and emit a header "@@ -a,b +c,d @@" followed by the hunk lines. A range start is the 1-based first line, or the line before when the count is 0; a count of 1 is omitted.

Why this case matters

Unified diff output depends on hunk grouping, context trimming and the header conventions for empty and single-line ranges.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
single change in the middle	`["@@ -4,4 +4,4 @@", " c3", "-old", "+new", " c4", " c5"]`	`["@@ -3,5 +3,5 @@", " c2", " c3", "-old", "+new", " c4", " c5"]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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