fix: fix infinite loop on expressions resolving only inside a DST for…

…ward jump (#938)

## Description

Removes a superfluous `+ 1` modifying the behavior unexpectedly. Using
the debugger I've located the bug to this instruction, and it can easily
be confirmed that this `+ 1` is the issue, since `date.month` &
`this.month` are both indexed starting from `1` (and not `0`).

Not sure how long this bug has been around, but it was [already present
when we aligned with the UNIX
standard](https://github.com/kelektiv/node-cron/pull/667/files#diff-c14c2dca8456f15417b39cfbd9758009f8eb4f3a190a415768d6e4ae6ae9dceeL473-L477).

## Related Issue

Fixes #919.

## Motivation and Context

Fixes an infinite loop when a cron expression only resolves to inside a
DST jump. See #919 for more.

## How Has This Been Tested?

Added two new test cases, and [made sure they triggered the infinite
loop](https://github.com/kelektiv/node-cron/actions/runs/12539141178/attempts/1?pr=938)
before writing the fix.

## Screenshots (if appropriate):

## Types of changes

<!--- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->

- [X] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)

## Checklist:

- [X] My code follows the code style of this project.
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [X] I have added tests to cover my changes.
- [X] All new and existing tests passed.
- [ ] If my change introduces a breaking change, I have added a `!`
after the type/scope in the title (see the Conventional Commits
standard).

.vscode/launch.json

@@ -7,7 +7,7 @@
 			"name": "Jest Debug",
 			"env": { "NODE_ENV": "test" },
 			"program": "${workspaceFolder}/node_modules/.bin/jest",
-			"args": [],
+			"args": ["--runInBand"],
 			"console": "integratedTerminal",
 			"windows": {
 				"program": "${workspaceFolder}/node_modules/jest/bin/jest"

src/time.ts

@@ -465,7 +465,7 @@ export class CronTime {
 		const beforeJumpingPoint = afterJumpingPoint.minus({ second: 1 });
 
 		if (
-			date.month + 1 in this.month &&
+			date.month in this.month &&
 			date.day in this.dayOfMonth &&
 			this._getWeekDay(date) in this.dayOfWeek
 		) {

tests/cron.test.ts

@@ -1299,4 +1299,53 @@ describe('cron', () => {
 			expect(job.running).toBe(false);
 		});
 	});
+
+	describe('Daylight Saving Time', () => {
+		// https://github.com/kelektiv/node-cron/issues/919
+		it('should not get into an infinite loop on Lisbon DST forward jump', () => {
+			const d = DateTime.fromISO('2024-03-30T00:59:59', {
+				zone: 'Europe/Lisbon'
+			}).toJSDate();
+			const clock = sinon.useFakeTimers(d.getTime());
+
+			console.debug({ d });
+
+			const job = new CronJob(
+				'0 1 30 3 *',
+				callback,
+				null,
+				true,
+				'Europe/Lisbon'
+			);
+
+			clock.tick(1000);
+			expect(callback).toHaveBeenCalledTimes(1);
+
+			clock.restore();
+			job.stop();
+		});
+
+		it('should not get into an infinite loop on Paris DST forward jump', () => {
+			const d = DateTime.fromISO('2024-03-31T01:59:59', {
+				zone: 'Europe/Paris'
+			}).toJSDate();
+			const clock = sinon.useFakeTimers(d.getTime());
+
+			console.debug({ d });
+
+			const job = new CronJob(
+				'0 2 31 3 *',
+				callback,
+				null,
+				true,
+				'Europe/Paris'
+			);
+
+			clock.tick(1000);
+			expect(callback).toHaveBeenCalledTimes(1);
+
+			clock.restore();
+			job.stop();
+		});
+	});
 });