Duration.diff returns negative number

[joshua0308]

Describe the bug
I get a negative number for a diff although the end date is after the start date.

To Reproduce

const start = DateTime.fromISO("2022-05-05T23:00", { zone: "UTC" });
const end = DateTime.fromISO("2022-05-10T00:00", { zone: "Europe/Madrid" }); // 2022-05-09T22:00Z
const diff = end.diff(start, ['days', 'hours', 'minutes']).toObject();

// diff === { days: 4, hours: -1, minutes: 0 }

Actual vs Expected behavior
I expect the diff to equal { days: 3, hours: 23, minutes: 0} instead of { days: 4, hours: -1, minutes: 0 }. It seems unintuitive to me that I have to think about adding and then subtracting to get to the diff.

Desktop (please complete the following information):

• OS: Mac OS
• Browser Chrome 99
• Luxon version 2.3.1
• Your timezone "America/New_York"

[JoaoAugustoPansani]

May I try to fix this?

[icambron]

@JoaoAugustoPansani sure

[JoaoAugustoPansani]

Hi @icambron , I don't have permission to make a branch, so I'll propose the solution:

On the file ./scripts/src/impl/diff.js there's a function dayDiff:

function dayDiff(earlier, later) {
  const utcDayStart = (dt) => dt.toUTC(0, { keepLocalTime: true }).startOf("day").valueOf(),
    ms = utcDayStart(later) - utcDayStart(earlier);
  return Math.floor(Duration.fromMillis(ms).as("days"));
}

What I did for solving this issue, was delete the second argument inside .toUTC:

function dayDiff(earlier, later) {
  const utcDayStart = (dt) => dt.toUTC(0).startOf("day").valueOf(),
    ms = utcDayStart(later) - utcDayStart(earlier);
  return Math.floor(Duration.fromMillis(ms).as("days"));
}

Then I wrote a test inside ./scripts/test/datetime/diff.test.js:

test("DateTime#diff works when date has a zone object", () => {
  const start = DateTime.fromISO("2022-05-05T23:00", { zone: "UTC" });
  const end = DateTime.fromISO("2022-05-10T00:00", { zone: "Europe/Madrid" });

  const diff = end.diff(start, ["days", "hours", "minutes"]).toObject();
  expect(diff.days).toBe(3);
  expect(diff.hours).toBe(23);
  expect(diff.minutes).toBe(0);
});

It worked, and didn't crash any other test.
Hope I helped with this one.

[icambron]

@JoaoAugustoPansani on github, instead of making a branch on my repository, you create a fork so that you have your own Luxon repository, then you make your changes there as you see fit on whatever branch you want, and then you post a PR across the repos.