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FA-75581 / Text diff and three-way merge / Open access

Character diff cleanup merge: insertions are emitted before deletions · case 01

The same replacement normalizes to insertion-first output, unlike the canonical form.

Verified by executionVariant 1 · 10 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The grouped insertion is appended before the grouped deletion.

THE FAILURE

The grouped insertion is appended before the grouped deletion.

Unsuccessful approach: Ordering the two edits by their text makes the order depend on content.

Case contract

Normalize a character diff of [op, text] (op -1 delete, 0 equal, 1 insert): drop empty texts, merge adjacent equalities, collect each run of edits into one deletion and one insertion (deletion first), move their common prefix into the preceding equality (creating one at the start if needed) and their common suffix into the following equality (appending one at the end if needed).

Why this case matters

Character-level diff engines normalize raw edit scripts so that the same change always renders the same way.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(diffs):
    res = []
    diffs = [list(d) for d in diffs if d[1] != '']
    i = 0
    while i < len(diffs):
        if diffs[i][0] == 0:
            if res and res[-1][0] == 0:
                res[-1][1] += diffs[i][1]
            else:
                res.append([0, diffs[i][1]])
            i += 1
            continue
        dl = ins = ''
        while i < len(diffs) and diffs[i][0] != 0:
            if diffs[i][0] == -1:
                dl += diffs[i][1]
            else:
                ins += diffs[i][1]
            i += 1
        suffix = ''
        if dl and ins:
            p = 0
            while p < min(len(dl), len(ins)) and dl[p] == ins[p]:
                p += 1
            if p:
                if res and res[-1][0] == 0:
                    res[-1][1] += dl[:p]
                else:
                    res.append([0, dl[:p]])
                dl, ins = dl[p:], ins[p:]
            s = 0
            while s < min(len(dl), len(ins)) and dl[-1 - s] == ins[-1 - s]:
                s += 1
            suffix = dl[len(dl) - s:]
            dl, ins = dl[:len(dl) - s], ins[:len(ins) - s]
        if ins:
            res.append([1, ins])
        if dl:
            res.append([-1, dl])
        if suffix:
            if i < len(diffs) and diffs[i][0] == 0:
                diffs[i] = [0, suffix + diffs[i][1]]
            else:
                res.append([0, suffix])
    return res
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = {
    1: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz1'], [1, 'uvz1']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z1']]), ('prefix at the start of the text', [[[-1, 'prea'], [1, 'preb'], [0, 'tail']]], [[0, 'pre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab1'], [0, ''], [1, 'ac1']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '1']])],
    2: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz2'], [1, 'uvz2']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z2']]), ('prefix at the start of the text', [[[-1, 'preprea'], [1, 'prepreb'], [0, 'tail']]], [[0, 'prepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab2'], [0, ''], [1, 'ac2']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '2']])],
    3: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz3'], [1, 'uvz3']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z3']]), ('prefix at the start of the text', [[[-1, 'prepreprea'], [1, 'preprepreb'], [0, 'tail']]], [[0, 'preprepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab3'], [0, ''], [1, 'ac3']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '3']])],
    4: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz4'], [1, 'uvz4']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z4']]), ('prefix at the start of the text', [[[-1, 'preprepreprea'], [1, 'prepreprepreb'], [0, 'tail']]], [[0, 'prepreprepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab4'], [0, ''], [1, 'ac4']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '4']])],
    5: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz5'], [1, 'uvz5']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z5']]), ('prefix at the start of the text', [[[-1, 'prepreprepreprea'], [1, 'preprepreprepreb'], [0, 'tail']]], [[0, 'preprepreprepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab5'], [0, ''], [1, 'ac5']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '5']])],
}[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 fixtureActualExpectedOutcome
adjacent equalities merge[[0, 'abcd']][[0, 'abcd']]Passed
empty entries are dropped[[0, 'a'], [1, 'b']][[0, 'a'], [1, 'b']]Passed
common prefix moves into the previous equality[[0, 'xab'], [1, 'd'], [-1, 'c'], [0, 'y']][[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]Failed
common suffix moves into the next equality[[0, 'p'], [1, 'm'], [-1, 'k'], [0, 'zq']][[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]Failed
no common affix[[0, 'h'], [1, 'cd'], [-1, 'ab'], [0, 'e']][[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]Failed
interleaved edits are grouped deletion first[[1, 'IJ'], [-1, 'DE']][[-1, 'DE'], [1, 'IJ']]Failed
suffix at the end of the text[[0, 'st'], [1, 'uv'], [-1, 'xy'], [0, 'z1']][[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z1']]Failed
prefix at the start of the text[[0, 'pre'], [1, 'b'], [-1, 'a'], [0, 'tail']][[0, 'pre'], [-1, 'a'], [1, 'b'], [0, 'tail']]Failed
insertion only[[0, 'a'], [1, 'b'], [0, 'c']][[0, 'a'], [1, 'b'], [0, 'c']]Passed
empty equality between edits[[0, 'ka'], [1, 'c'], [-1, 'b'], [0, '1']][[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '1']]Failed

SHA-256 / b978cb7af1fed701ad64076404c4404fdfd84f79e65a7b4ea62cf78cd423e5f9

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(diffs):
    res = []
    diffs = [list(d) for d in diffs if d[1] != '']
    i = 0
    while i < len(diffs):
        if diffs[i][0] == 0:
            if res and res[-1][0] == 0:
                res[-1][1] += diffs[i][1]
            else:
                res.append([0, diffs[i][1]])
            i += 1
            continue
        dl = ins = ''
        while i < len(diffs) and diffs[i][0] != 0:
            if diffs[i][0] == -1:
                dl += diffs[i][1]
            else:
                ins += diffs[i][1]
            i += 1
        suffix = ''
        if dl and ins:
            p = 0
            while p < min(len(dl), len(ins)) and dl[p] == ins[p]:
                p += 1
            if p:
                if res and res[-1][0] == 0:
                    res[-1][1] += dl[:p]
                else:
                    res.append([0, dl[:p]])
                dl, ins = dl[p:], ins[p:]
            s = 0
            while s < min(len(dl), len(ins)) and dl[-1 - s] == ins[-1 - s]:
                s += 1
            suffix = dl[len(dl) - s:]
            dl, ins = dl[:len(dl) - s], ins[:len(ins) - s]
        res.extend(sorted([x for x in ([-1, dl], [1, ins]) if x[1]], key=lambda d: d[1]))
        if suffix:
            if i < len(diffs) and diffs[i][0] == 0:
                diffs[i] = [0, suffix + diffs[i][1]]
            else:
                res.append([0, suffix])
    return res
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = {
    1: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz1'], [1, 'uvz1']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z1']]), ('prefix at the start of the text', [[[-1, 'prea'], [1, 'preb'], [0, 'tail']]], [[0, 'pre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab1'], [0, ''], [1, 'ac1']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '1']])],
    2: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz2'], [1, 'uvz2']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z2']]), ('prefix at the start of the text', [[[-1, 'preprea'], [1, 'prepreb'], [0, 'tail']]], [[0, 'prepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab2'], [0, ''], [1, 'ac2']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '2']])],
    3: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz3'], [1, 'uvz3']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z3']]), ('prefix at the start of the text', [[[-1, 'prepreprea'], [1, 'preprepreb'], [0, 'tail']]], [[0, 'preprepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab3'], [0, ''], [1, 'ac3']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '3']])],
    4: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz4'], [1, 'uvz4']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z4']]), ('prefix at the start of the text', [[[-1, 'preprepreprea'], [1, 'prepreprepreb'], [0, 'tail']]], [[0, 'prepreprepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab4'], [0, ''], [1, 'ac4']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '4']])],
    5: [('adjacent equalities merge', [[[0, 'ab'], [0, 'cd']]], [[0, 'abcd']]), ('empty entries are dropped', [[[0, 'a'], [-1, ''], [1, 'b'], [0, '']]], [[0, 'a'], [1, 'b']]), ('common prefix moves into the previous equality', [[[0, 'x'], [-1, 'abc'], [1, 'abd'], [0, 'y']]], [[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]), ('common suffix moves into the next equality', [[[0, 'p'], [-1, 'kz'], [1, 'mz'], [0, 'q']]], [[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]), ('no common affix', [[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]], [[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]), ('interleaved edits are grouped deletion first', [[[1, 'I'], [-1, 'D'], [1, 'J'], [-1, 'E']]], [[-1, 'DE'], [1, 'IJ']]), ('suffix at the end of the text', [[[0, 'st'], [-1, 'xyz5'], [1, 'uvz5']]], [[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z5']]), ('prefix at the start of the text', [[[-1, 'prepreprepreprea'], [1, 'preprepreprepreb'], [0, 'tail']]], [[0, 'preprepreprepre'], [-1, 'a'], [1, 'b'], [0, 'tail']]), ('insertion only', [[[0, 'a'], [1, 'b'], [0, 'c']]], [[0, 'a'], [1, 'b'], [0, 'c']]), ('empty equality between edits', [[[0, 'k'], [-1, 'ab5'], [0, ''], [1, 'ac5']]], [[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '5']])],
}[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 fixtureActualExpectedOutcome
adjacent equalities merge[[0, 'abcd']][[0, 'abcd']]Passed
empty entries are dropped[[0, 'a'], [1, 'b']][[0, 'a'], [1, 'b']]Passed
common prefix moves into the previous equality[[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']][[0, 'xab'], [-1, 'c'], [1, 'd'], [0, 'y']]Passed
common suffix moves into the next equality[[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']][[0, 'p'], [-1, 'k'], [1, 'm'], [0, 'zq']]Passed
no common affix[[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']][[0, 'h'], [-1, 'ab'], [1, 'cd'], [0, 'e']]Passed
interleaved edits are grouped deletion first[[-1, 'DE'], [1, 'IJ']][[-1, 'DE'], [1, 'IJ']]Passed
suffix at the end of the text[[0, 'st'], [1, 'uv'], [-1, 'xy'], [0, 'z1']][[0, 'st'], [-1, 'xy'], [1, 'uv'], [0, 'z1']]Failed
prefix at the start of the text[[0, 'pre'], [-1, 'a'], [1, 'b'], [0, 'tail']][[0, 'pre'], [-1, 'a'], [1, 'b'], [0, 'tail']]Passed
insertion only[[0, 'a'], [1, 'b'], [0, 'c']][[0, 'a'], [1, 'b'], [0, 'c']]Passed
empty equality between edits[[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '1']][[0, 'ka'], [-1, 'b'], [1, 'c'], [0, '1']]Passed

SHA-256 / 09f67414726607e1b3f18be8a6b386941ecf2ade7057227272ea3ce2a63369c7

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 10 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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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 2026-09-29T14:49:08.147244+00:00.

Case digest / 3eb004cf2e0d4a3e50a45f8f92fd8d317c60c99fba79891402185d47fd61f720