FA-75401 / Text diff and three-way merge / Open access

Unified hunk builder: leading context is measured from the last change of a group · case 01

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

Verified by executionVariant 1 · 11 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The hunk start subtracts the context width from the group end instead of the group start.

VERIFIED REPAIR

Start the hunk up to C lines before the first change of the group.

Unsuccessful approach: Measuring from the start but one line short drops one leading context line from every hunk.

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.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ops, context):
    changes = [i for i, op in enumerate(ops) if op[0] != ' ']
    if not changes:
        return []
    groups = []
    start = end = changes[0]
    for i in changes[1:]:
        if i - end - 1 <= 2 * context:
            end = i
        else:
            groups.append((start, end))
            start = end = i
    groups.append((start, end))
    old_no, new_no = [], []
    o = w = 0
    for tag, _ in ops:
        old_no.append(o)
        new_no.append(w)
        if tag != '+':
            o += 1
        if tag != '-':
            w += 1
    def rng(start0, count):
        first = start0 + 1 if count > 0 else start0
        return str(first) if count == 1 else '%d,%d' % (first, count)
    out = []
    for s, e in groups:
        lo = max(0, e - context)
        hi = min(len(ops) - 1, e + context)
        body = ops[lo:hi + 1]
        ol = sum(1 for t, _ in body if t != '+')
        nl = sum(1 for t, _ in body if t != '-')
        out.append('@@ -%s +%s @@' % (rng(old_no[lo], ol), rng(new_no[lo], nl)))
        out.extend(t + x for t, x in body)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = {
    1: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0']], 3], ['@@ -0,0 +1 @@', '+x0']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 1], ['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 1], ['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    2: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1']], 3], ['@@ -0,0 +1,2 @@', '+x0', '+x1']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 2], ['@@ -1,7 +1,7 @@', '-a', ' c0', ' c1', ' c2', ' c3', '+b', ' c0', ' c1']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 2], ['@@ -1,3 +1,2 @@', '-a', ' c0', ' c1', '@@ -5,4 +4,5 @@', ' c3', ' c4', '+b', ' c0', ' c1']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    3: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2']], 3], ['@@ -0,0 +1,3 @@', '+x0', '+x1', '+x2']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 3], ['@@ -1,10 +1,10 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 3], ['@@ -1,4 +1,3 @@', '-a', ' c0', ' c1', ' c2', '@@ -6,6 +5,7 @@', ' c4', ' c5', ' c6', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    4: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2'], ['+', 'x3']], 3], ['@@ -0,0 +1,4 @@', '+x0', '+x1', '+x2', '+x3']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 4], ['@@ -1,12 +1,12 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', ' c6', ' c7', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 4], ['@@ -1,5 +1,4 @@', '-a', ' c0', ' c1', ' c2', ' c3', '@@ -7,7 +6,8 @@', ' c5', ' c6', ' c7', ' c8', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    5: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2'], ['+', 'x3'], ['+', 'x4']], 3], ['@@ -0,0 +1,5 @@', '+x0', '+x1', '+x2', '+x3', '+x4']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], [' ', 'c9'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 5], ['@@ -1,14 +1,14 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', ' c6', ' c7', ' c8', ' c9', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], [' ', 'c9'], [' ', 'c10'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 5], ['@@ -1,6 +1,5 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', '@@ -8,8 +7,9 @@', ' c6', ' c7', ' c8', ' c9', ' c10', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
}[N]
for label, args, expected in cases:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

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
change at the very start	`['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']`	`['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']`	Passed
pure insertion into an empty file	`['@@ -0,0 +1 @@', '+x0']`	`['@@ -0,0 +1 @@', '+x0']`	Passed
pure deletion of every line	`['@@ -1 +0,0 @@', '-gone']`	`['@@ -1 +0,0 @@', '-gone']`	Passed
two changes separated by exactly twice the context	`['@@ -3,2 +2,3 @@', ' c1', '+b', ' c0']`	`['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']`	Failed
two changes separated by more than twice the context	`['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']`	`['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']`	Passed
insertion after existing lines	`['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']`	`['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']`	Passed
single-line ranges	`['@@ -4,0 +4 @@', '+y']`	`['@@ -4 +4 @@', '-x', '+y']`	Failed
no changes	`[]`	`[]`	Passed
deletion and insertion in separate hunks	`['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']`	`['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']`	Passed
deletion near the start with wide context	`['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2']`	`['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2']`	Passed

SHA-256 / 8496235582229ee597cd37f95c92c44e26dffa08e94ee80bd30523f403e09502

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ops, context):
    changes = [i for i, op in enumerate(ops) if op[0] != ' ']
    if not changes:
        return []
    groups = []
    start = end = changes[0]
    for i in changes[1:]:
        if i - end - 1 <= 2 * context:
            end = i
        else:
            groups.append((start, end))
            start = end = i
    groups.append((start, end))
    old_no, new_no = [], []
    o = w = 0
    for tag, _ in ops:
        old_no.append(o)
        new_no.append(w)
        if tag != '+':
            o += 1
        if tag != '-':
            w += 1
    def rng(start0, count):
        first = start0 + 1 if count > 0 else start0
        return str(first) if count == 1 else '%d,%d' % (first, count)
    out = []
    for s, e in groups:
        lo = max(0, s - context + 1)
        hi = min(len(ops) - 1, e + context)
        body = ops[lo:hi + 1]
        ol = sum(1 for t, _ in body if t != '+')
        nl = sum(1 for t, _ in body if t != '-')
        out.append('@@ -%s +%s @@' % (rng(old_no[lo], ol), rng(new_no[lo], nl)))
        out.extend(t + x for t, x in body)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = {
    1: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0']], 3], ['@@ -0,0 +1 @@', '+x0']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 1], ['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 1], ['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    2: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1']], 3], ['@@ -0,0 +1,2 @@', '+x0', '+x1']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 2], ['@@ -1,7 +1,7 @@', '-a', ' c0', ' c1', ' c2', ' c3', '+b', ' c0', ' c1']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 2], ['@@ -1,3 +1,2 @@', '-a', ' c0', ' c1', '@@ -5,4 +4,5 @@', ' c3', ' c4', '+b', ' c0', ' c1']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    3: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2']], 3], ['@@ -0,0 +1,3 @@', '+x0', '+x1', '+x2']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 3], ['@@ -1,10 +1,10 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 3], ['@@ -1,4 +1,3 @@', '-a', ' c0', ' c1', ' c2', '@@ -6,6 +5,7 @@', ' c4', ' c5', ' c6', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    4: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2'], ['+', 'x3']], 3], ['@@ -0,0 +1,4 @@', '+x0', '+x1', '+x2', '+x3']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 4], ['@@ -1,12 +1,12 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', ' c6', ' c7', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 4], ['@@ -1,5 +1,4 @@', '-a', ' c0', ' c1', ' c2', ' c3', '@@ -7,7 +6,8 @@', ' c5', ' c6', ' c7', ' c8', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    5: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2'], ['+', 'x3'], ['+', 'x4']], 3], ['@@ -0,0 +1,5 @@', '+x0', '+x1', '+x2', '+x3', '+x4']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], [' ', 'c9'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 5], ['@@ -1,14 +1,14 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', ' c6', ' c7', ' c8', ' c9', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], [' ', 'c9'], [' ', 'c10'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 5], ['@@ -1,6 +1,5 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', '@@ -8,8 +7,9 @@', ' c6', ' c7', ' c8', ' c9', ' c10', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
}[N]
for label, args, expected in cases:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

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
change at the very start	`['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']`	`['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']`	Passed
pure insertion into an empty file	`['@@ -0,0 +1 @@', '+x0']`	`['@@ -0,0 +1 @@', '+x0']`	Passed
pure deletion of every line	`['@@ -1 +0,0 @@', '-gone']`	`['@@ -1 +0,0 @@', '-gone']`	Passed
two changes separated by exactly twice the context	`['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']`	`['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']`	Passed
two changes separated by more than twice the context	`['@@ -1,2 +1 @@', '-a', ' c0', '@@ -5 +4,2 @@', '+b', ' c0']`	`['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']`	Failed
insertion after existing lines	`['@@ -5 +5,2 @@', ' c4', '+tail']`	`['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']`	Failed
single-line ranges	`['@@ -4,0 +4 @@', '+y']`	`['@@ -4 +4 @@', '-x', '+y']`	Failed
no changes	`[]`	`[]`	Passed
deletion and insertion in separate hunks	`['@@ -2,0 +1,0 @@', '@@ -3,0 +3,0 @@']`	`['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']`	Failed
deletion near the start with wide context	`['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2']`	`['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2']`	Passed

SHA-256 / 0f96ca038a3e503d245f73093568a015b21cfd5031640ad76ff0c8187781e32f

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ops, context):
    changes = [i for i, op in enumerate(ops) if op[0] != ' ']
    if not changes:
        return []
    groups = []
    start = end = changes[0]
    for i in changes[1:]:
        if i - end - 1 <= 2 * context:
            end = i
        else:
            groups.append((start, end))
            start = end = i
    groups.append((start, end))
    old_no, new_no = [], []
    o = w = 0
    for tag, _ in ops:
        old_no.append(o)
        new_no.append(w)
        if tag != '+':
            o += 1
        if tag != '-':
            w += 1
    def rng(start0, count):
        first = start0 + 1 if count > 0 else start0
        return str(first) if count == 1 else '%d,%d' % (first, count)
    out = []
    for s, e in groups:
        lo = max(0, s - context)
        hi = min(len(ops) - 1, e + context)
        body = ops[lo:hi + 1]
        ol = sum(1 for t, _ in body if t != '+')
        nl = sum(1 for t, _ in body if t != '-')
        out.append('@@ -%s +%s @@' % (rng(old_no[lo], ol), rng(new_no[lo], nl)))
        out.extend(t + x for t, x in body)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = {
    1: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0']], 3], ['@@ -0,0 +1 @@', '+x0']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 1], ['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 1], ['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    2: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1']], 3], ['@@ -0,0 +1,2 @@', '+x0', '+x1']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 2], ['@@ -1,7 +1,7 @@', '-a', ' c0', ' c1', ' c2', ' c3', '+b', ' c0', ' c1']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 2], ['@@ -1,3 +1,2 @@', '-a', ' c0', ' c1', '@@ -5,4 +4,5 @@', ' c3', ' c4', '+b', ' c0', ' c1']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    3: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2']], 3], ['@@ -0,0 +1,3 @@', '+x0', '+x1', '+x2']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 3], ['@@ -1,10 +1,10 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 3], ['@@ -1,4 +1,3 @@', '-a', ' c0', ' c1', ' c2', '@@ -6,6 +5,7 @@', ' c4', ' c5', ' c6', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    4: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2'], ['+', 'x3']], 3], ['@@ -0,0 +1,4 @@', '+x0', '+x1', '+x2', '+x3']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 4], ['@@ -1,12 +1,12 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', ' c6', ' c7', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 4], ['@@ -1,5 +1,4 @@', '-a', ' c0', ' c1', ' c2', ' c3', '@@ -7,7 +6,8 @@', ' c5', ' c6', ' c7', ' c8', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
    5: [('single change in the middle', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], ['-', 'old'], ['+', 'new'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7']], 2], ['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']), ('change at the very start', [[['-', 'first'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4']], 3], ['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']), ('pure insertion into an empty file', [[['+', 'x0'], ['+', 'x1'], ['+', 'x2'], ['+', 'x3'], ['+', 'x4']], 3], ['@@ -0,0 +1,5 @@', '+x0', '+x1', '+x2', '+x3', '+x4']), ('pure deletion of every line', [[['-', 'gone']], 1], ['@@ -1 +0,0 @@', '-gone']), ('two changes separated by exactly twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], [' ', 'c9'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 5], ['@@ -1,14 +1,14 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', ' c5', ' c6', ' c7', ' c8', ' c9', '+b', ' c0', ' c1', ' c2']), ('two changes separated by more than twice the context', [[['-', 'a'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5'], [' ', 'c6'], [' ', 'c7'], [' ', 'c8'], [' ', 'c9'], [' ', 'c10'], ['+', 'b'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 5], ['@@ -1,6 +1,5 @@', '-a', ' c0', ' c1', ' c2', ' c3', ' c4', '@@ -8,8 +7,9 @@', ' c6', ' c7', ' c8', ' c9', ' c10', '+b', ' c0', ' c1', ' c2']), ('insertion after existing lines', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], ['+', 'tail']], 2], ['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']), ('single-line ranges', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], ['-', 'x'], ['+', 'y'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2']], 0], ['@@ -4 +4 @@', '-x', '+y']), ('no changes', [[[' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3']], 3], []), ('deletion and insertion in separate hunks', [[[' ', 'a'], ['-', 'b'], [' ', 'c'], ['+', 'd'], [' ', 'e']], 0], ['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']), ('deletion near the start with wide context', [[[' ', 'c0'], ['-', 'd1'], ['-', 'd2'], [' ', 'c0'], [' ', 'c1'], [' ', 'c2'], [' ', 'c3'], [' ', 'c4'], [' ', 'c5']], 3], ['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2'])],
}[N]
for label, args, expected in cases:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
single change in the middle	`['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']`	`['@@ -3,5 +3,5 @@', ' c2', ' c3', '-old', '+new', ' c4', ' c5']`	Passed
change at the very start	`['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']`	`['@@ -1,4 +1,3 @@', '-first', ' c0', ' c1', ' c2']`	Passed
pure insertion into an empty file	`['@@ -0,0 +1 @@', '+x0']`	`['@@ -0,0 +1 @@', '+x0']`	Passed
pure deletion of every line	`['@@ -1 +0,0 @@', '-gone']`	`['@@ -1 +0,0 @@', '-gone']`	Passed
two changes separated by exactly twice the context	`['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']`	`['@@ -1,4 +1,4 @@', '-a', ' c0', ' c1', '+b', ' c0']`	Passed
two changes separated by more than twice the context	`['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']`	`['@@ -1,2 +1 @@', '-a', ' c0', '@@ -4,2 +3,3 @@', ' c2', '+b', ' c0']`	Passed
insertion after existing lines	`['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']`	`['@@ -4,2 +4,3 @@', ' c3', ' c4', '+tail']`	Passed
single-line ranges	`['@@ -4 +4 @@', '-x', '+y']`	`['@@ -4 +4 @@', '-x', '+y']`	Passed
no changes	`[]`	`[]`	Passed
deletion and insertion in separate hunks	`['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']`	`['@@ -2 +1,0 @@', '-b', '@@ -3,0 +3 @@', '+d']`	Passed
deletion near the start with wide context	`['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2']`	`['@@ -1,6 +1,4 @@', ' c0', '-d1', '-d2', ' c0', ' c1', ' c2']`	Passed

SHA-256 / b5f1348407f6694091c078ea031a065d5743fe8fd44b61e3b6df6bc0ac17aba8

Verification & scope

A deterministic, bounded teaching model of one diff, patch or merge rule with stipulated conventions; it is not a production diff or version-control implementation and makes no claim of conformance to any specific tool. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:49:06.090590+00:00.

Case digest / 78ed42e34196b9f20989cc92c11059f35bff271c86ffd4875d365187c36d840d