FAILURE MAP
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FA-80636 / Bidirectional text layout / Open access

Caret visual position: trailing edge side · case 01

Carets after RTL characters are drawn past them.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The trailing edge ignores direction and always uses the right side.

VERIFIED REPAIR

Trailing edge is right for LTR and left for RTL.

Unsuccessful approach: Subtracting one for RTL overshoots to the left.

Case contract

Input [levels, logical caret offset k, affinity]. Characters are one unit wide and visually ordered by level reversal. Affinity "after" attaches the caret to the leading edge of character k (if k < n), otherwise to the trailing edge of character k-1; offset 0 always uses the leading edge of character 0. The leading edge of an LTR character is its left side, of an RTL (odd) character its right side. Return the visual x.

Why this case matters

Mixed right-to-left and left-to-right text must resolve levels and visual order exactly, or words, numbers and carets land in the wrong place.

1 / The failure

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

N = 1
observations = []
def solve(x):
    def reorder(lv):
        vis = list(range(len(lv)))
        odd = [l for l in lv if l % 2 == 1]
        if not odd:
            return vis
        for lev in range(max(lv), min(odd) - 1, -1):
            i = 0
            while i < len(vis):
                if lv[vis[i]] >= lev:
                    j = i
                    while j < len(vis) and lv[vis[j]] >= lev:
                        j += 1
                    vis[i:j] = vis[i:j][::-1]
                    i = j
                else:
                    i += 1
        return vis
    
    levels, k, affinity = x
    n = len(levels)
    if n == 0:
        return 0
    vis = reorder(levels)
    pos = [0] * n
    for v, i in enumerate(vis):
        pos[i] = v
    if affinity == 'after' and k < n or k == 0:
        j = k
        leading = True
    else:
        j = k - 1
        leading = False
    rtl = levels[j] % 2 == 1
    if leading:
        return pos[j] + 1 if rtl else pos[j]
    return pos[j] + 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('line end', [[1, 1, 1], 3, 'after'], 0), ('regression: trailing edge side', [[3, 3, 3, 3, 3, 3, 1, 1], 7, 'before'], 1), ('regression: trailing edge side', [[1, 1, 1, 1, 1, 1, 0, 0, 0, 0], 6, 'before'], 0), ('regression: trailing edge side', [[2, 2, 2, 3, 3, 2, 2, 2, 3, 3], 10, 'after'], 8), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('line start before', [[1, 1, 0], 0, 'before'], 2), ('control layout', [[2, 2], 2, 'after'], 2), ('control layout', [[1, 2, 2, 1], 3, 'after'], 1)], [('regression: trailing edge side', [[1, 1, 1, 1, 3, 3, 1, 1], 1, 'before'], 7), ('regression: trailing edge side', [[3, 3, 3, 3, 2, 2, 2, 0, 0], 2, 'before'], 2), ('regression: trailing edge side', [[3, 3, 3, 3, 1, 4, 4, 1, 2, 1], 10, 'after'], 0), ('regression: trailing edge side', [[2, 1], 2, 'after'], 0), ('line end', [[1, 1, 1], 3, 'after'], 0), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('control layout', [[0], 1, 'before'], 1), ('control layout', [[3, 3, 3, 1, 1, 0, 0, 0, 0, 0], 5, 'after'], 5)], [('regression: trailing edge side', [[1, 1, 1, 1, 1, 1], 2, 'before'], 4), ('regression: trailing edge side', [[0, 0, 0, 1, 3, 3, 3, 3], 6, 'before'], 5), ('regression: trailing edge side', [[2, 1, 1, 1, 1], 5, 'after'], 0), ('regression: trailing edge side', [[2, 2, 2, 2, 3, 3, 3, 1, 1, 1], 10, 'before'], 0), ('line end', [[1, 1, 1], 3, 'after'], 0), ('line start before', [[1, 1, 0], 0, 'before'], 2), ('control layout', [[1, 1, 1, 1, 1, 1, 1], 1, 'after'], 6), ('control layout', [[3, 3, 3], 0, 'after'], 3)], [('regression: trailing edge side', [[3, 3, 3, 3], 1, 'before'], 3), ('regression: trailing edge side', [[3, 3, 3, 2, 2, 3, 3, 3, 3, 2], 9, 'before'], 5), ('regression: trailing edge side', [[1, 3, 3], 3, 'before'], 0), ('regression: trailing edge side', [[2, 2, 1, 1, 3, 2, 2, 3], 4, 'before'], 4), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('control layout', [[0, 0, 3, 0, 2], 3, 'after'], 3), ('control layout', [[3, 3, 0, 0, 0], 3, 'before'], 3)], [('regression: trailing edge side', [[0, 1, 1, 2, 2, 2, 3, 3, 3, 1], 3, 'before'], 8), ('regression: trailing edge side', [[1], 1, 'after'], 0), ('regression: trailing edge side', [[1, 3, 3, 1, 1, 1, 1, 1], 2, 'before'], 6), ('regression: trailing edge side', [[1, 1, 2, 2, 1, 1, 1], 2, 'before'], 5), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('control layout', [[1, 1, 1, 1, 0, 1, 1, 1, 1], 0, 'before'], 4), ('control layout', [[3, 3, 0, 0, 0], 5, 'after'], 5)]]
for label, args, expected in fixtures[N - 1]:
    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
line end10Failed
regression: trailing edge side21Failed
regression: trailing edge side10Failed
regression: trailing edge side98Failed
same boundary after44Passed
line start before22Passed
control layout22Passed
control layout11Passed

SHA-256 / 1f7cdb4e10763e1e1e4838d26ad591ed96b34d63322ca65eb6528e1108519a10

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    def reorder(lv):
        vis = list(range(len(lv)))
        odd = [l for l in lv if l % 2 == 1]
        if not odd:
            return vis
        for lev in range(max(lv), min(odd) - 1, -1):
            i = 0
            while i < len(vis):
                if lv[vis[i]] >= lev:
                    j = i
                    while j < len(vis) and lv[vis[j]] >= lev:
                        j += 1
                    vis[i:j] = vis[i:j][::-1]
                    i = j
                else:
                    i += 1
        return vis
    
    levels, k, affinity = x
    n = len(levels)
    if n == 0:
        return 0
    vis = reorder(levels)
    pos = [0] * n
    for v, i in enumerate(vis):
        pos[i] = v
    if affinity == 'after' and k < n or k == 0:
        j = k
        leading = True
    else:
        j = k - 1
        leading = False
    rtl = levels[j] % 2 == 1
    if leading:
        return pos[j] + 1 if rtl else pos[j]
    return pos[j] - 1 if rtl else pos[j] + 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('line end', [[1, 1, 1], 3, 'after'], 0), ('regression: trailing edge side', [[3, 3, 3, 3, 3, 3, 1, 1], 7, 'before'], 1), ('regression: trailing edge side', [[1, 1, 1, 1, 1, 1, 0, 0, 0, 0], 6, 'before'], 0), ('regression: trailing edge side', [[2, 2, 2, 3, 3, 2, 2, 2, 3, 3], 10, 'after'], 8), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('line start before', [[1, 1, 0], 0, 'before'], 2), ('control layout', [[2, 2], 2, 'after'], 2), ('control layout', [[1, 2, 2, 1], 3, 'after'], 1)], [('regression: trailing edge side', [[1, 1, 1, 1, 3, 3, 1, 1], 1, 'before'], 7), ('regression: trailing edge side', [[3, 3, 3, 3, 2, 2, 2, 0, 0], 2, 'before'], 2), ('regression: trailing edge side', [[3, 3, 3, 3, 1, 4, 4, 1, 2, 1], 10, 'after'], 0), ('regression: trailing edge side', [[2, 1], 2, 'after'], 0), ('line end', [[1, 1, 1], 3, 'after'], 0), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('control layout', [[0], 1, 'before'], 1), ('control layout', [[3, 3, 3, 1, 1, 0, 0, 0, 0, 0], 5, 'after'], 5)], [('regression: trailing edge side', [[1, 1, 1, 1, 1, 1], 2, 'before'], 4), ('regression: trailing edge side', [[0, 0, 0, 1, 3, 3, 3, 3], 6, 'before'], 5), ('regression: trailing edge side', [[2, 1, 1, 1, 1], 5, 'after'], 0), ('regression: trailing edge side', [[2, 2, 2, 2, 3, 3, 3, 1, 1, 1], 10, 'before'], 0), ('line end', [[1, 1, 1], 3, 'after'], 0), ('line start before', [[1, 1, 0], 0, 'before'], 2), ('control layout', [[1, 1, 1, 1, 1, 1, 1], 1, 'after'], 6), ('control layout', [[3, 3, 3], 0, 'after'], 3)], [('regression: trailing edge side', [[3, 3, 3, 3], 1, 'before'], 3), ('regression: trailing edge side', [[3, 3, 3, 2, 2, 3, 3, 3, 3, 2], 9, 'before'], 5), ('regression: trailing edge side', [[1, 3, 3], 3, 'before'], 0), ('regression: trailing edge side', [[2, 2, 1, 1, 3, 2, 2, 3], 4, 'before'], 4), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('control layout', [[0, 0, 3, 0, 2], 3, 'after'], 3), ('control layout', [[3, 3, 0, 0, 0], 3, 'before'], 3)], [('regression: trailing edge side', [[0, 1, 1, 2, 2, 2, 3, 3, 3, 1], 3, 'before'], 8), ('regression: trailing edge side', [[1], 1, 'after'], 0), ('regression: trailing edge side', [[1, 3, 3, 1, 1, 1, 1, 1], 2, 'before'], 6), ('regression: trailing edge side', [[1, 1, 2, 2, 1, 1, 1], 2, 'before'], 5), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('control layout', [[1, 1, 1, 1, 0, 1, 1, 1, 1], 0, 'before'], 4), ('control layout', [[3, 3, 0, 0, 0], 5, 'after'], 5)]]
for label, args, expected in fixtures[N - 1]:
    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
line end-10Failed
regression: trailing edge side01Failed
regression: trailing edge side-10Failed
regression: trailing edge side78Failed
same boundary after44Passed
line start before22Passed
control layout22Passed
control layout11Passed

SHA-256 / 9f530632039d8d3b9894b992e78dfdb7ddd2ef86325168271fb73b1cb4fcb6d5

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    def reorder(lv):
        vis = list(range(len(lv)))
        odd = [l for l in lv if l % 2 == 1]
        if not odd:
            return vis
        for lev in range(max(lv), min(odd) - 1, -1):
            i = 0
            while i < len(vis):
                if lv[vis[i]] >= lev:
                    j = i
                    while j < len(vis) and lv[vis[j]] >= lev:
                        j += 1
                    vis[i:j] = vis[i:j][::-1]
                    i = j
                else:
                    i += 1
        return vis
    
    levels, k, affinity = x
    n = len(levels)
    if n == 0:
        return 0
    vis = reorder(levels)
    pos = [0] * n
    for v, i in enumerate(vis):
        pos[i] = v
    if affinity == 'after' and k < n or k == 0:
        j = k
        leading = True
    else:
        j = k - 1
        leading = False
    rtl = levels[j] % 2 == 1
    if leading:
        return pos[j] + 1 if rtl else pos[j]
    return pos[j] if rtl else pos[j] + 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('line end', [[1, 1, 1], 3, 'after'], 0), ('regression: trailing edge side', [[3, 3, 3, 3, 3, 3, 1, 1], 7, 'before'], 1), ('regression: trailing edge side', [[1, 1, 1, 1, 1, 1, 0, 0, 0, 0], 6, 'before'], 0), ('regression: trailing edge side', [[2, 2, 2, 3, 3, 2, 2, 2, 3, 3], 10, 'after'], 8), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('line start before', [[1, 1, 0], 0, 'before'], 2), ('control layout', [[2, 2], 2, 'after'], 2), ('control layout', [[1, 2, 2, 1], 3, 'after'], 1)], [('regression: trailing edge side', [[1, 1, 1, 1, 3, 3, 1, 1], 1, 'before'], 7), ('regression: trailing edge side', [[3, 3, 3, 3, 2, 2, 2, 0, 0], 2, 'before'], 2), ('regression: trailing edge side', [[3, 3, 3, 3, 1, 4, 4, 1, 2, 1], 10, 'after'], 0), ('regression: trailing edge side', [[2, 1], 2, 'after'], 0), ('line end', [[1, 1, 1], 3, 'after'], 0), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('control layout', [[0], 1, 'before'], 1), ('control layout', [[3, 3, 3, 1, 1, 0, 0, 0, 0, 0], 5, 'after'], 5)], [('regression: trailing edge side', [[1, 1, 1, 1, 1, 1], 2, 'before'], 4), ('regression: trailing edge side', [[0, 0, 0, 1, 3, 3, 3, 3], 6, 'before'], 5), ('regression: trailing edge side', [[2, 1, 1, 1, 1], 5, 'after'], 0), ('regression: trailing edge side', [[2, 2, 2, 2, 3, 3, 3, 1, 1, 1], 10, 'before'], 0), ('line end', [[1, 1, 1], 3, 'after'], 0), ('line start before', [[1, 1, 0], 0, 'before'], 2), ('control layout', [[1, 1, 1, 1, 1, 1, 1], 1, 'after'], 6), ('control layout', [[3, 3, 3], 0, 'after'], 3)], [('regression: trailing edge side', [[3, 3, 3, 3], 1, 'before'], 3), ('regression: trailing edge side', [[3, 3, 3, 2, 2, 3, 3, 3, 3, 2], 9, 'before'], 5), ('regression: trailing edge side', [[1, 3, 3], 3, 'before'], 0), ('regression: trailing edge side', [[2, 2, 1, 1, 3, 2, 2, 3], 4, 'before'], 4), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('control layout', [[0, 0, 3, 0, 2], 3, 'after'], 3), ('control layout', [[3, 3, 0, 0, 0], 3, 'before'], 3)], [('regression: trailing edge side', [[0, 1, 1, 2, 2, 2, 3, 3, 3, 1], 3, 'before'], 8), ('regression: trailing edge side', [[1], 1, 'after'], 0), ('regression: trailing edge side', [[1, 3, 3, 1, 1, 1, 1, 1], 2, 'before'], 6), ('regression: trailing edge side', [[1, 1, 2, 2, 1, 1, 1], 2, 'before'], 5), ('same boundary after', [[0, 0, 1, 1], 2, 'after'], 4), ('caret at direction boundary', [[0, 0, 1, 1], 2, 'before'], 2), ('control layout', [[1, 1, 1, 1, 0, 1, 1, 1, 1], 0, 'before'], 4), ('control layout', [[3, 3, 0, 0, 0], 5, 'after'], 5)]]
for label, args, expected in fixtures[N - 1]:
    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
line end00Passed
regression: trailing edge side11Passed
regression: trailing edge side00Passed
regression: trailing edge side88Passed
same boundary after44Passed
line start before22Passed
control layout22Passed
control layout11Passed

SHA-256 / 3cd4f3ad4177a4391bb2a5b4a884719199f560eadd071fc0ebb12215949de1b5

Verification & scope

A deterministic toy bidi model over stipulated class labels and integer levels; it is inspired by, but does not claim conformance to, any published algorithm. 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 2026-09-29T14:49:55.538918+00:00.

Case digest / 99b03eacad0d57a3fdc1f06ef598b109fa3dc868bf1defc23183642653aa2ac2