FA-75394 / Text diff and three-way merge / Member archive

Unified hunk builder: empty ranges start at the next line · case 04

Headers for pure insertions or deletions point one line too far, so patch tools apply them in the wrong place.

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
pure insertion into an empty file	`["@@ -1,0 +1,4 @@", "+x0", "+x1", "+x2", "+x3"]`	`["@@ -0,0 +1,4 @@", "+x0", "+x1", "+x2", "+x3"]`	Failed

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

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