fix(ext/cron): automatically override unspecified values (#22042)

Fixes #22041

cli/tests/unit/cron_test.ts

@@ -391,3 +391,70 @@ Deno.test("error on two handlers", () => {
     "Deno.cron requires a single handler",
   );
 });
+
+Deno.test("Parse test", () => {
+  assertEquals(
+    parseScheduleToString({
+      minute: 3,
+    }),
+    "3 * * * *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      hour: { every: 2 },
+    }),
+    "0 */2 * * *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      dayOfMonth: { every: 10 },
+    }),
+    "0 0 */10 * *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      month: { every: 3 },
+    }),
+    "0 0 1 */3 *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      dayOfWeek: { every: 2 },
+    }),
+    "0 0 * * */2",
+  );
+  assertEquals(
+    parseScheduleToString({
+      minute: 3,
+      hour: { every: 2 },
+    }),
+    "3 */2 * * *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      dayOfMonth: { start: 1, end: 10 },
+    }),
+    "0 0 1-10 * *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      minute: { every: 10 },
+      dayOfMonth: { every: 5 },
+    }),
+    "*/10 * */5 * *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      hour: { every: 3 },
+      month: { every: 2 },
+    }),
+    "0 */3 * */2 *",
+  );
+  assertEquals(
+    parseScheduleToString({
+      minute: { every: 5 },
+      month: { every: 2 },
+    }),
+    "*/5 * * */2 *",
+  );
+});

ext/cron/01_cron.ts

@@ -62,14 +62,33 @@ export function parseScheduleToString(
   if (typeof schedule === "string") {
     return schedule;
   } else {
-    const {
+    let {
       minute,
       hour,
       dayOfMonth,
       month,
       dayOfWeek,
     } = schedule;
 
+    // Automatically override unspecified values for convenience. For example,
+    // to run every 2 hours, `{ hour: { every: 2 } }` can be specified without
+    // explicitely specifying `minute`.
+    if (minute !== undefined) {
+      // Nothing to override.
+    } else if (hour !== undefined) {
+      // Override minute to 0 since it's not specified.
+      minute = 0;
+    } else if (dayOfMonth !== undefined || dayOfWeek !== undefined) {
+      // Override minute and hour to 0 since they're not specified.
+      minute = 0;
+      hour = 0;
+    } else if (month !== undefined) {
+      // Override minute and hour to 0, and dayOfMonth to 1 since they're not specified.
+      minute = 0;
+      hour = 0;
+      dayOfMonth = 1;
+    }
+
     return formatToCronSchedule(minute) +
       " " + formatToCronSchedule(hour) +
       " " + formatToCronSchedule(dayOfMonth) +