Fix due dates not rendering with a one-off date

web_src/js/features/midnight.js

@@ -0,0 +1,22 @@
+// Some timestamps are not meant to be localized in the user's timezone, only in their language.
+// This is true for due date timestamps. These include a specific year, month, and day combination. If a user in one timezone
+// sets the date YYYY-MM-DD, another user should see the same date, regardless of their timezone. So when a relative-time element
+// has their datetime attribute specified only as YYYY-MM-DD, we will update it to YYYY-MM-DD midnight in the user's timezone.
+// When the date is rendered, the only localization that will happen is the language.
+
+const dateRegex = /^\d{4}-\d{2}-\d{2}$/;
+
+// for all relative-time elements, if their datetime attribute is YYYY-MM-DD, we will update it to YYYY-MM-DD midnight in the user's timezone
+export function initMidnightRelativeTime() {
+  const relativeTimeElements = document.querySelectorAll('relative-time[datetime]');
+
+  for (const element of relativeTimeElements) {
+    const datetimeAttr = element.getAttribute('datetime');
+
+    if (dateRegex.test(datetimeAttr)) {
+      const [year, month, day] = datetimeAttr.split('-');
+      const userMidnight = new Date(year, month - 1, day);
+      element.setAttribute('datetime', userMidnight.toISOString());
+    }
+  }
+}

web_src/js/index.js

@@ -85,12 +85,14 @@ import {initRepoRecentCommits} from './features/recent-commits.js';
 import {initRepoDiffCommitBranchesAndTags} from './features/repo-diff-commit.js';
 import {initDirAuto} from './modules/dirauto.js';
 import {initRepositorySearch} from './features/repo-search.js';
+import {initMidnightRelativeTime} from './features/midnight.js';
 
 // Init Gitea's Fomantic settings
 initGiteaFomantic();
 initDirAuto();
 
 onDomReady(() => {
+  initMidnightRelativeTime();
   initGlobalCommon();
 
   initGlobalTooltips();