Hide target selector if tag exists when creating new release (#23171)

Close #22649.

|status|screenshot|
|-|-|
|empty tag name|<img
src="https://user-images.githubusercontent.com/15528715/221490165-fd3abd2e-6dc5-4562-bece-d1d6a305479e.png"
width="300px"/>|
|new tag|<img
src="https://user-images.githubusercontent.com/15528715/221490450-49b2a48e-b206-49f4-bd79-34b1ea64156f.png"
width="300px"/>|
|existing tag|<img
src="https://user-images.githubusercontent.com/15528715/221490301-4d1879dd-4947-4abc-9b9a-e77be1806981.png"
width="300px"/>|

2 files changed, 39 insertions, 4 deletions

diff --git a/web_src/js/features/repo-release.js b/web_src/js/features/repo-release.js
index a061c6b23..a230d7765 100644
--- a/web_src/js/features/repo-release.js
+++ b/web_src/js/features/repo-release.js
@@ -3,7 +3,7 @@ import {attachTribute} from './tribute.js';
 import {initCompMarkupContentPreviewTab} from './comp/MarkupContentPreview.js';
 import {initEasyMDEImagePaste} from './comp/ImagePaste.js';
 import {createCommentEasyMDE} from './comp/EasyMDE.js';
-import {hideElem} from '../utils/dom.js';
+import {hideElem, showElem} from '../utils/dom.js';
 
 export function initRepoRelease() {
   $(document).on('click', '.remove-rel-attach', function() {
@@ -14,8 +14,43 @@ export function initRepoRelease() {
   });
 }
 
+export function initRepoReleaseNew() {
+  const $repoReleaseNew = $('.repository.new.release');
+  if (!$repoReleaseNew.length) return;
 
-export function initRepoReleaseEditor() {
+  initTagNameEditor();
+  initRepoReleaseEditor();
+}
+
+function initTagNameEditor() {
+  const el = document.getElementById('tag-name-editor');
+  if (!el) return;
+
+  const existingTags = JSON.parse(el.getAttribute('data-existing-tags'));
+  if (!Array.isArray(existingTags)) return;
+
+  const defaultTagHelperText = el.getAttribute('data-tag-helper');
+  const newTagHelperText = el.getAttribute('data-tag-helper-new');
+  const existingTagHelperText = el.getAttribute('data-tag-helper-existing');
+
+  document.getElementById('tag-name').addEventListener('keyup', (e) => {
+    const value = e.target.value;
+    if (existingTags.includes(value)) {
+      // If the tag already exists, hide the target branch selector.
+      hideElem('#tag-target-selector');
+      document.getElementById('tag-helper').innerText = existingTagHelperText;
+    } else {
+      showElem('#tag-target-selector');
+      if (value) {
+        document.getElementById('tag-helper').innerText = newTagHelperText;
+      } else {
+        document.getElementById('tag-helper').innerText = defaultTagHelperText;
+      }
+    }
+  });
+}
+
+function initRepoReleaseEditor() {
   const $editor = $('.repository.new.release .content-editor');
   if ($editor.length === 0) {
     return;
diff --git a/web_src/js/index.js b/web_src/js/index.js
index 611c09d2b..6b4f4ef3e 100644
--- a/web_src/js/index.js
+++ b/web_src/js/index.js
@@ -76,7 +76,7 @@ import {
 import {initViewedCheckboxListenerFor} from './features/pull-view-file.js';
 import {initOrgTeamSearchRepoBox, initOrgTeamSettings} from './features/org-team.js';
 import {initUserAuthWebAuthn, initUserAuthWebAuthnRegister} from './features/user-auth-webauthn.js';
-import {initRepoRelease, initRepoReleaseEditor} from './features/repo-release.js';
+import {initRepoRelease, initRepoReleaseNew} from './features/repo-release.js';
 import {initRepoEditor} from './features/repo-editor.js';
 import {initCompSearchUserBox} from './features/comp/SearchUserBox.js';
 import {initInstall} from './features/install.js';
@@ -179,7 +179,7 @@ $(document).ready(() => {
   initRepoPullRequestAllowMaintainerEdit();
   initRepoPullRequestReview();
   initRepoRelease();
-  initRepoReleaseEditor();
+  initRepoReleaseNew();
   initRepoSettingGitHook();
   initRepoSettingSearchTeamBox();
   initRepoSettingsCollaboration();