fix(pat-recurrence): Fix the RRULE date format for additional RDATE dates.

src/pat/recurrence/recurrence.js

@@ -218,17 +218,21 @@ function widgetSaveToRfc5545(form, RDATE, EXDATE, conf, tz) {
 
         for (let rdate of RDATE) {
             if (rdate !== "") {
-                // RDATE values are "YYYY-MM-DD"
+                // The values from the input field are ISO8601 "YYYY-MM-DD"
+                // RFC5545 expects a date or date-time format of e.g.
+                // "YYYYMMDD". See:‌
+                // https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.5.2
+                rdate = rdate.replaceAll("-", "");
                 // by adding "T000000" the recurrence sequence generator of
                 // plone.event.recurrence adds the current start time correctly
-                rdate += rdate.length === 10 ? "T000000" : "";
+                rdate += rdate.length === 8 ? "T000000" : "";
                 rdate += tz ? "Z" : "";
                 tmp_dates.push(rdate);
 
                 // human readable RDATE
                 year = parseInt(rdate.substring(0, 4), 10);
-                month = parseInt(rdate.substring(5, 7), 10) - 1;
-                day = parseInt(rdate.substring(8, 10), 10);
+                month = parseInt(rdate.substring(4, 6), 10) - 1; // js month.
+                day = parseInt(rdate.substring(6, 8), 10);
                 tmp_human.push(
                     format(
                         new Date(year, month, day),

src/pat/recurrence/recurrence.test.js

@@ -95,4 +95,46 @@ describe("Recurrence", function () {
         const add_occurrence = document.querySelector(".modal .riaddoccurrence");
         expect(add_occurrence).toBeTruthy();
     });
+
+    it("Adds EXDATES as expected by RFC5545.", async function () {
+        // This fixes a problem described in
+        // https://github.com/plone/plone.formwidget.recurrence/issues/48
+        // A RDATE needs to follow RFC5545 date or date-time format. See:
+        // https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.5.2
+        document.body.innerHTML = `
+            <input name="start" type="date" value="2026-01-01" />
+            <textarea class="pat-recurrence"
+                      data-pat-recurrence='{
+                          "startField": "[name=start]",
+                          "allowAdditionalDates": true
+                      }'
+            ></textarea>
+        `;
+
+        registry.scan(document.body);
+        await utils.timeout(1);
+
+        const edit_btn = document.querySelector("[name=riedit]");
+        edit_btn.click();
+
+        const add_date = document.querySelector(".modal #adddate");
+        add_date.value = "2026-01-14";
+        const add_date_btn = document.querySelector(".modal #addaction");
+        add_date_btn.click();
+
+        const jq = (await import("jquery")).default;
+        jq.fn.ajaxSubmit = () => {};
+
+        // Save
+        const save_btn = document.querySelector(".modal .risavebutton");
+        save_btn.click();
+
+        // modal is closed now.
+        const modal = document.querySelector(".modal");
+        expect(modal).toBeFalsy();
+
+        const recurrence = document.querySelector(".pat-recurrence");
+        expect(recurrence.value).toContain("RRULE:FREQ=DAILY");
+        expect(recurrence.value).toContain("RDATE:20260114T000000");
+    });
 });