Fix issue oncall schedule expiry

.github/workflow-scripts/__tests__/extractIssueOncalls-test.js

@@ -31,6 +31,7 @@ describe('extractIssueOncalls', () => {
   });
 
   afterEach(() => {
+    jest.restoreAllMocks();
     jest.useRealTimers();
   });
   it('extracts m and f on 6 of April', () => {
@@ -80,4 +81,16 @@ describe('extractIssueOncalls', () => {
     const oncalls = extractIssueOncalls(schedule, userMap);
     expect(oncalls).toEqual([userMap['@g'], userMap['@d']]);
   });
+
+  it('continues the latest rotation after the schedule ends', () => {
+    const warn = jest.spyOn(console, 'warn').mockImplementation(() => {});
+    jest.setSystemTime(new Date(2025, 3, 15));
+
+    const oncalls = extractIssueOncalls(schedule, userMap);
+
+    expect(oncalls).toEqual([userMap['@g'], userMap['@d']]);
+    expect(warn).toHaveBeenCalledWith(
+      'No issue oncall schedule found for 2025-04-15; continuing the rotation from 2025-04-08',
+    );
+  });
 });

.github/workflow-scripts/extractIssueOncalls.js

@@ -20,8 +20,23 @@ function extractUsersFromScheduleAndDate(schedule, userMap, date) {
   const month = date.getMonth() + 1; // 0 is January, 1 is February
   const day = date.getDate();
   const dateStr = `${year}-${month < 10 ? `0${month}` : month}-${day < 10 ? `0${day}` : day}`;
-  const user1 = userMap[schedule[dateStr][0]];
-  const user2 = userMap[schedule[dateStr][1]];
+  const scheduledDate = Object.keys(schedule)
+    .filter(candidateDate => candidateDate <= dateStr)
+    .sort()
+    .at(-1);
+
+  if (scheduledDate == null) {
+    throw new Error(`No issue oncall schedule found on or before ${dateStr}`);
+  }
+
+  if (scheduledDate !== dateStr) {
+    console.warn(
+      `No issue oncall schedule found for ${dateStr}; continuing the rotation from ${scheduledDate}`,
+    );
+  }
+
+  const user1 = userMap[schedule[scheduledDate][0]];
+  const user2 = userMap[schedule[scheduledDate][1]];
   return [user1, user2];
 }
 
@@ -47,6 +62,8 @@ function extractUsersFromScheduleAndDate(schedule, userMap, date) {
  * }
  * ```
  *
+ * Each dated entry stays active until a newer entry takes effect.
+ *
  * When uploading the secret, make sure that the JSON strings are escaped!
  * The script will fail otherwise, because GitHub will remove the `"` characters.
  */