fix: strptime swaps day/year for DD-MM-YYYY dates

[Koan-Bot]

What

Fix strptime returning swapped day/year values when parsing European-style dates (DD-MM-YYYY).

Why

strptime("31-12-2023") returned day=2023, month=11, year=31 instead of day=31, month=11, year=123. This made str2time("31-12-2023") return undef since day=2023 is invalid. Any date where the first field exceeds 12 and the last field is the year (e.g., "25-07-2020") was broken.

How

The existing swap logic on line 143 assumed $1 (first numeric field) was always a year when $month > 12. This is only true for YYYY-MM-DD (mainframe format where $1 > 31). For DD-MM-YYYY format ($1 <= 31), the year is in $5 and the day in $1. Added a check to distinguish the two cases.

Testing

• New t/ddmmyyyy.t with 12 tests covering DD-MM-YYYY, DD-MM-YY, and YYYY-MM-DD formats
• Full test suite passes (592 tests)

🤖 Generated with Claude Code

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Quality Report

Changes: 2 files changed, 46 insertions(+), 2 deletions(-)

Code scan: clean

Tests: skipped

Branch hygiene: clean

Generated by Kōan post-mission quality pipeline

[greptile-apps]

Greptile Summary

This PR fixes strptime swapping day and year for European-style DD-MM-YYYY dates by distinguishing YYYY-MM-DD (first field > 31) from DD-MM-YYYY (first field ≤ 31) when the initial month parse produces an out-of-range value.

• P1 — off-by-one in boundary condition: The guard on line 143 is $month > 12, which equals $1 > 13. Dates where the day field is exactly 13 (e.g. \"13-06-2023\") yield $month = 12, and 12 > 12 is false, so no swap occurs. The result is an invalid month=12 (0-based), and str2time still returns undef. The condition should be $month >= 12.

Confidence Score: 4/5

Not safe to merge as-is — the off-by-one in the boundary condition leaves day=13 dates still broken after the fix

One P1 defect remains: $month > 12 should be $month >= 12. Dates with day=13 (e.g. "13-06-2023") still produce an invalid month and return undef from str2time. The fix is a one-character change and the tests cover the rest of the logic correctly.

lib/Date/Parse.pm line 143 — boundary condition off-by-one

Important Files Changed

Filename	Overview
lib/Date/Parse.pm	Fixes DD-MM-YYYY day/year swap but off-by-one in boundary condition (> 12 instead of >= 12) leaves day=13 dates still broken
t/ddmmyyyy.t	New test file covering DD-MM-YYYY, DD-MM-YY, and YYYY-MM-DD formats; misses a day=13 boundary case that would expose the remaining off-by-one bug

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Regex match: (\\d+)-(\\d\\d?)-(\\d+)\n$1=first, $3=middle, $5=last"] --> B["Initial assignment:\nmonth = $1 - 1\nday = $3\nyear = $5"]
    B --> C{"month > 12?\ni.e. $1 > 13"}
    C -- No --> G["Keep: month=$1-1, day=$3, year=$5\n⚠️ day=13 falls here incorrectly"]
    C -- Yes --> D{"$1 > 31?"}
    D -- Yes --> E["YYYY-MM-DD\nyear=$1, month=$3-1, day=$5"]
    D -- No --> F["DD-MM-YYYY\nyear=$5, month=$3-1, day=$1"]
    E --> H["return if year > 2 digits and year < 1901"]
    F --> H
    G --> H
    style G fill:#ffcccc,stroke:#cc0000

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_{Reviews (1): Last reviewed commit: "fix: strptime swaps day/year for DD-MM-Y..." | Re-trigger Greptile}

[greptile-apps]

Off-by-one: day=13 in DD-MM-YYYY still broken

The condition $month > 12 translates to ($1 - 1) > 12, i.e. $1 > 13. That means a date like "13-06-2023" produces $month = 12 (invalid 0-based month) and never enters the fix branch — 12 > 12 is false. The result would be month=12, day=6, year=2023 (month 12 is out of range), so str2time("13-06-2023") still returns undef. The check should be $month >= 12 (i.e. $1 > 12) to cover any first-field value that cannot be a valid month.

Suggested change

	if ($month > 12) {
	if ($month >= 12) {

[greptile-apps]

Comment overstates fix coverage; boundary case untested

The comment says "the first field exceeds 12" but every test case uses a day ≥ 25. The exact boundary the current code misses — day=13, where $month = 12 and 12 > 12 is false — has no test. Adding a case like strptime("13-06-2023") would catch the off-by-one in the > 12 vs >= 12 condition and match the comment's stated invariant.