From 51a0bc1014afbfe24f26d24c3507112a4cdd89aa Mon Sep 17 00:00:00 2001
From: Michael Villari <mikevillari@gmail.com>
Date: Thu, 17 Sep 2026 13:03:37 -0400
Subject: [PATCH] Validate calendar dates in date and date-time formats

---
 src/parser/jsonParser.ts | 16 +++++++++++++++-
 src/test/parser.test.ts  | 28 ++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/src/parser/jsonParser.ts b/src/parser/jsonParser.ts
index 658ab8d..64c9828 100644
--- a/src/parser/jsonParser.ts
+++ b/src/parser/jsonParser.ts
@@ -31,6 +31,18 @@ const formats = {
 	'ipv6': { errorMessage: l10n.t('String is not an IPv6 address.'), pattern: /^((([0-9a-f]{1,4}:){7}([0-9a-f]{1,4}|:))|(([0-9a-f]{1,4}:){6}(:[0-9a-f]{1,4}|((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9a-f]{1,4}:){5}(((:[0-9a-f]{1,4}){1,2})|:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3})|:))|(([0-9a-f]{1,4}:){4}(((:[0-9a-f]{1,4}){1,3})|((:[0-9a-f]{1,4})?:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9a-f]{1,4}:){3}(((:[0-9a-f]{1,4}){1,4})|((:[0-9a-f]{1,4}){0,2}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9a-f]{1,4}:){2}(((:[0-9a-f]{1,4}){1,5})|((:[0-9a-f]{1,4}){0,3}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(([0-9a-f]{1,4}:){1}(((:[0-9a-f]{1,4}){1,6})|((:[0-9a-f]{1,4}){0,4}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:))|(:(((:[0-9a-f]{1,4}){1,7})|((:[0-9a-f]{1,4}){0,5}:((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(\.(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)){3}))|:)))$/i },
 };
 
+// The date and date-time patterns check syntax; RFC 3339 section 5.7 also limits the day by month and year.
+function isValidDate(year: number, month: number, day: number): boolean {
+	let daysInMonth = 31;
+	if (month === 2) {
+		const isLeapYear = year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
+		daysInMonth = isLeapYear ? 29 : 28;
+	} else if (month === 4 || month === 6 || month === 9 || month === 11) {
+		daysInMonth = 30;
+	}
+	return day <= daysInMonth;
+}
+
 export interface IProblem {
 	location: IRange;
 	severity?: DiagnosticSeverity;
@@ -974,7 +986,9 @@ function validate(n: ASTNode | undefined, schema: JSONSchema, validationResult:
 				case 'ipv4':
 				case 'ipv6':
 					const format = formats[schema.format];
-					if (!node.value || !format.pattern.exec(node.value)) {
+					const match = format.pattern.exec(node.value);
+					const hasDate = schema.format === 'date' || schema.format === 'date-time';
+					if (!match || (hasDate && !isValidDate(Number(match[1]), Number(match[2]), Number(match[3])))) {
 						validationResult.problems.push({
 							location: { offset: node.offset, length: node.length },
 							message: schema.patternErrorMessage || schema.errorMessage || format.errorMessage
diff --git a/src/test/parser.test.ts b/src/test/parser.test.ts
index 25ae6d4..ac483c5 100644
--- a/src/test/parser.test.ts
+++ b/src/test/parser.test.ts
@@ -953,6 +953,34 @@ suite('JSON Parser', () => {
 		assert.strictEqual(semanticErrors![0].message, 'String is not a valid UUID.');
 	});
 
+	for (const format of ['date', 'date-time']) {
+		test(`${format} calendar dates`, function () {
+			const schema = { type: 'string', format };
+			const validDates = [
+				'2023-01-31', '2023-02-28', '2023-03-31', '2023-04-30',
+				'2023-05-31', '2023-06-30', '2023-07-31', '2023-08-31',
+				'2023-09-30', '2023-10-31', '2023-11-30', '2023-12-31',
+				'2024-02-29', '2000-02-29', '0000-02-29', '0096-02-29', '0400-02-29'
+			];
+			const invalidDates = [
+				'2023-02-29', '2023-02-30', '2024-02-30', '2024-02-31',
+				'2023-04-31', '2023-06-31', '2023-09-31', '2023-11-31',
+				'1900-02-29', '2100-02-29', '0100-02-29', '0001-02-29'
+			];
+			for (const date of validDates) {
+				const value = format === 'date' ? date : `${date}T23:30:00-02:00`;
+				assert.strictEqual(validate(JSON.stringify(value), schema)!.length, 0, value);
+			}
+			for (const date of invalidDates) {
+				const value = format === 'date' ? date : `${date}T00:30:00+02:00`;
+				const diagnostics = validate(JSON.stringify(value), schema)!;
+				assert.strictEqual(diagnostics.length, 1, value);
+				assert.strictEqual(diagnostics[0].message, `String is not a RFC3339 ${format}.`);
+				assert.deepStrictEqual(diagnostics[0].range, toRange(JSON.stringify(value), 0, value.length + 2));
+			}
+		});
+	}
+
 	test('Numbers', function () {
 
 		const str = '{"one": 13.45e+1}';