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Update difference() to fully support rounding
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Adds full rounding support to difference(). Fixes #1023. Notes:
* See #1023 for details on the algorithm.
* I added a bunch of new test cases for various DST-related edge cases.
* I suspect this algorothm can be simplified; it's not particularly DRY.
* This commit does *not* enable DST awareness in the `round` method.
  `round` currently works, but without any DST support which is OK for
  the time being. We can PR a DST-aware `round` in the next few weeks.
* The algorithm and/or implementation can probably be adapted for later
  use in `round`, as well as Duration's `add`, `subtract`, and `round`
  when `relativeTo` is a ZDT instance.  I can help with this next week.
* Docs updates for ZDT are not included in this commit. I'll file a new
  PR for docs changes next week.
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@justingrant
justingrant committed Oct 21, 2020
1 parent 7085495 commit 8777de8
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2 changes: 1 addition & 1 deletion package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@
"poc-postprocess": "node ./polyfill/lib/poc/postProcess.js",
"poc-rebuild": "cd polyfill && npm run build && rm -f *.tgz && npm pack",
"poc-compile": "npm run poc-tsc-noemit && npm run poc-dts-nocomments && npm run poc-dts && npm run poc-babel && npm run poc-babel-tests && npm run poc-postprocess && npm run poc-pretty && npm run poc-rebuild",
"poc-cnt": "npm run poc-compile && clear && npm run test-no262",
"poc-cnt": "npm run poc-compile && clear && printf '\\e[3J' && npm run test-no262",
"test-no262": "cd polyfill && npm install && npm test && npm run test-cookbook",
"test": "cd polyfill && npm install && npm test && npm run test-cookbook && npm run test262",
"codecov:tests": "cd polyfill && npm install && npm run codecov:tests",
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154 changes: 135 additions & 19 deletions polyfill/lib/poc/ZonedDateTime.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -238,22 +238,24 @@ describe('ZonedDateTime', () => {
equal(`${undo}`, `${start}`);
});

/* skipping this test until we fix difference()
it('Samoa date line change (subtract): 11:00PM 31 Dec 2011 -> 10:00PM 29 Dec 2011', () => {
const dayAfterSamoaDateLineChangeAbs = new Temporal.DateTime(2011, 12, 31, 23).toInstant('Pacific/Apia');
const start = dayAfterSamoaDateLineChangeAbs.toZonedDateTime('Pacific/Apia');
const added = start.subtract({ days: 1, hours: 1 });
equal(added.day, 29);
equal(added.hour, 22);
equal(added.minute, 0);
const diff = added.difference(start, { largestUnit: 'days' });
const skipped = start.subtract({ days: 1, hours: 1 });
equal(skipped.day, 31);
equal(skipped.hour, 22);
equal(skipped.minute, 0);
const end = start.subtract({ days: 2, hours: 1 });
equal(end.day, 29);
equal(end.hour, 22);
equal(end.minute, 0);
const diff = end.difference(start, { largestUnit: 'days' });
equal(diff.minutes, 0);
equal(diff.hours, -1);
equal(diff.days, -2);
const undo = added.subtract(diff);
equal(`${undo}`, `${start}`);
const undo = start.add(diff);
equal(`${undo}`, `${end}`);
});
*/

it('3:30 day before DST start -> 3:30 day of DST start', () => {
const start = dayBeforeDstStart.add({ hours: 1 }); // 3:30AM
Expand All @@ -278,11 +280,8 @@ describe('ZonedDateTime', () => {
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, 1);
// TODO: uncomment and revise these tests after
// difference algorithm round-trip issue is resolved.
// See https://mailarchive.ietf.org/arch/msg/calsify/9rPGjL2YRM6SUmW1uDY_wmZ4kPk/
// const undo = added.subtract(diff);
// equal(`${undo}`, `${dayBeforeDstStart}`);
const undo = dayBeforeDstStart.add(diff);
equal(`${undo}`, `${added}`);
});

it('1:30 day DST starts -> 4:30 day DST starts', () => {
Expand All @@ -309,11 +308,9 @@ describe('ZonedDateTime', () => {
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, 1);
// TODO: uncomment and revise these tests after
// difference algorithm round-trip issue is resolved.
// See https://mailarchive.ietf.org/arch/msg/calsify/9rPGjL2YRM6SUmW1uDY_wmZ4kPk/
// const undo = added.subtract(diff);
// equal(`${undo}`, `${start}`);

const undo = start.add(diff);
equal(`${undo}`, `${added}`);
});

it('1:00AM day DST starts -> (add 24 hours) -> 2:00AM day after DST starts', () => {
Expand Down Expand Up @@ -344,6 +341,125 @@ describe('ZonedDateTime', () => {
equal(`${undo}`, `${start}`);
});

it('Difference can return day length > 24 hours', () => {
const start = ZonedDateTime.from('2020-10-30T01:45-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-11-02T01:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { largestUnit: 'days' });
equal(diff.minutes, 30);
equal(diff.hours, 24);
equal(diff.days, 2);
const undo = start.add(diff);
equal(`${undo}`, `${end}`);
});

it('Difference rounding (nearest day) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { smallestUnit: 'days' }); // roundingMode: 'nearest'
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, -3);
});

it('Difference rounding (ceil day) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { smallestUnit: 'days', roundingMode: 'ceil' });
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, -2);
});

it('Difference rounding (trunc day) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { smallestUnit: 'days', roundingMode: 'trunc' });
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, -2);
});

it('Difference rounding (floor day) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { smallestUnit: 'days', roundingMode: 'floor' });
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, -3);
});

it('Difference rounding (nearest hour) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { largestUnit: 'days', smallestUnit: 'hours' }); // roundingMode: 'nearest'
equal(diff.minutes, 0);
equal(diff.hours, -12);
equal(diff.days, -2);
});

it('Difference rounding (ceil hour) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { largestUnit: 'days', smallestUnit: 'hours', roundingMode: 'ceil' });
equal(diff.minutes, 0);
equal(diff.hours, -12);
equal(diff.days, -2);
});

it('Difference rounding (trunc hour) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { largestUnit: 'days', smallestUnit: 'hours', roundingMode: 'trunc' });
equal(diff.minutes, 0);
equal(diff.hours, -12);
equal(diff.days, -2);
});

it('Difference rounding (floor hour) is DST-aware', () => {
const start = ZonedDateTime.from('2020-03-10T02:30-07:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-07T14:15-08:00[America/Los_Angeles]');
const diff = end.difference(start, { largestUnit: 'days', smallestUnit: 'hours', roundingMode: 'floor' });
equal(diff.minutes, 0);
equal(diff.hours, -13);
equal(diff.days, -2);
});

it('Difference when date portion ends inside a DST-skipped period', () => {
const start = ZonedDateTime.from('2020-03-07T02:30-08:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-03-08T03:15-07:00[America/Los_Angeles]');
const diff = end.difference(start, { largestUnit: 'days' });
equal(diff.minutes, 45);
equal(diff.hours, 23);
equal(diff.days, 0);
});

it("Difference when date portion ends inside day skipped by Samoa's 24hr 2011 transition", () => {
const end = ZonedDateTime.from('2011-12-31T05:00+14:00[Pacific/Apia]');
const start = ZonedDateTime.from('2011-12-28T10:00-10:00[Pacific/Apia]');
const diff = end.difference(start, { largestUnit: 'days' });
equal(diff.minutes, 0);
equal(diff.hours, 19);
equal(diff.days, 1);
});

it('Rounding up to hours causes one more day of overflow (positive)', () => {
const start = ZonedDateTime.from('2020-01-01T00:00-08:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-01-03T23:59-08:00[America/Los_Angeles]');
const diff = end.difference(start, { largestUnit: 'days', smallestUnit: 'hours' });
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, 3);
});

it('Rounding up to hours causes one more day of overflow (negative)', () => {
const start = ZonedDateTime.from('2020-01-01T00:00-08:00[America/Los_Angeles]');
const end = ZonedDateTime.from('2020-01-03T23:59-08:00[America/Los_Angeles]');
const diff = start.difference(end, { largestUnit: 'days', smallestUnit: 'hours' });
equal(diff.minutes, 0);
equal(diff.hours, 0);
equal(diff.days, -3);
});

it('addition and difference work near DST start', () => {
// Test the difference between different distances near DST start
const stepsPerHour = 2;
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