feat(mentions,tags): tag mentions (#3769)

* feat: add tag search Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * feat(mentions): tag mentions backend Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * feat: tag mention design Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * refactor: revamp mentions autocomplete Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * fix: unauthorized mention of hidden groups Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * feat(mentions,tags): use hash format for tag mentions Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * refactor: frontend mention format API with mentionable models Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * feat: implement tag search on the frontend Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * fix: tag color contrast Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * fix: tag suggestions styling Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * test: works with disabled tags extension Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * chore: move `MentionFormats` to `formats` Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * fix: mentions preview bad styling Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * docs: further migration location clarification Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * Apply fixes from StyleCI * fix: bad test namespace Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * fix: phpstan Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * fix: conditionally add tag related extenders Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * Apply fixes from StyleCI * feat(phpstan): evaluate conditional extenders Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> * feat: use mithril routing for tag mentions Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> --------- Signed-off-by: Sami Mazouz <sychocouldy@gmail.com> Co-authored-by: StyleCI Bot <bot@styleci.io>
2025-08-01 14:10:37 +02:00 · 2023-04-19 12:58:11 +01:00
parent b868c3d763
commit 5e281136f6
46 changed files with 1788 additions and 366 deletions
--- a/extensions/mentions/composer.json
+++ b/extensions/mentions/composer.json
@@ -33,6 +33,9 @@
        "flarum-extension": {
            "title": "Mentions",
            "category": "feature",
+            "optional-dependencies": [
+                "flarum/tags"
+            ],
            "icon": {
                "name": "fas fa-at",
                "backgroundColor": "#539EC1",
@@ -74,6 +77,7 @@
    },
    "require-dev": {
        "flarum/core": "*@dev",
+        "flarum/tags": "*@dev",
        "flarum/testing": "^1.0.0"
    },
    "repositories": [
--- a/extensions/mentions/extend.php
+++ b/extensions/mentions/extend.php
@@ -26,6 +26,8 @@ use Flarum\Post\Event\Restored;
 use Flarum\Post\Event\Revised;
 use Flarum\Post\Filter\PostFilterer;
 use Flarum\Post\Post;
+use Flarum\Tags\Api\Serializer\TagSerializer;
+use Flarum\Tags\Tag;
 use Flarum\User\User;

 return [
@@ -42,14 +44,14 @@ return [
        ->render(Formatter\FormatUserMentions::class)
        ->render(Formatter\FormatGroupMentions::class)
        ->unparse(Formatter\UnparsePostMentions::class)
-        ->unparse(Formatter\UnparseUserMentions::class)
-        ->parse(Formatter\CheckPermissions::class),
+        ->unparse(Formatter\UnparseUserMentions::class),

    (new Extend\Model(Post::class))
        ->belongsToMany('mentionedBy', Post::class, 'post_mentions_post', 'mentions_post_id', 'post_id')
        ->belongsToMany('mentionsPosts', Post::class, 'post_mentions_post', 'post_id', 'mentions_post_id')
        ->belongsToMany('mentionsUsers', User::class, 'post_mentions_user', 'post_id', 'mentions_user_id')
-        ->belongsToMany('mentionsGroups', Group::class, 'post_mentions_group', 'post_id', 'mentions_group_id'),
+        ->belongsToMany('mentionsGroups', Group::class, 'post_mentions_group', 'post_id', 'mentions_group_id')
+        ->belongsToMany('mentionsUsers', User::class, 'post_mentions_user', 'post_id', 'mentions_user_id'),

    new Extend\Locales(__DIR__.'/locale'),

@@ -83,7 +85,7 @@ return [
    (new Extend\ApiController(Controller\ListDiscussionsController::class))
        ->load([
            'firstPost.mentionsUsers', 'firstPost.mentionsPosts', 'firstPost.mentionsPosts.user', 'firstPost.mentionsGroups',
-            'lastPost.mentionsUsers', 'lastPost.mentionsPosts', 'lastPost.mentionsPosts.user', 'lastPost.mentionsGroups'
+            'lastPost.mentionsUsers', 'lastPost.mentionsPosts', 'lastPost.mentionsPosts.user', 'lastPost.mentionsGroups',
        ]),

    (new Extend\ApiController(Controller\ShowPostController::class))
@@ -99,12 +101,6 @@ return [
        ->loadWhere('mentionedBy', [LoadMentionedByRelationship::class, 'mutateRelation'])
        ->prepareDataForSerialization([LoadMentionedByRelationship::class, 'countRelation']),

-    (new Extend\ApiController(Controller\CreatePostController::class))
-        ->addOptionalInclude('mentionsGroups'),
-
-    (new Extend\ApiController(Controller\UpdatePostController::class))
-        ->addOptionalInclude('mentionsGroups'),
-
    (new Extend\Settings)
        ->serializeToForum('allowUsernameMentionFormat', 'flarum-mentions.allow_username_format', 'boolval'),

@@ -121,7 +117,32 @@ return [
        ->addFilter(Filter\MentionedPostFilter::class),

    (new Extend\ApiSerializer(CurrentUserSerializer::class))
-        ->attribute('canMentionGroups', function (CurrentUserSerializer $serializer, User $user, array $attributes): bool {
+        ->attribute('canMentionGroups', function (CurrentUserSerializer $serializer, User $user): bool {
            return $user->can('mentionGroups');
-        })
+        }),
+
+    // Tag mentions
+    (new Extend\Conditional())
+        ->whenExtensionEnabled('flarum-tags', [
+            (new Extend\Formatter)
+                ->render(Formatter\FormatTagMentions::class)
+                ->unparse(Formatter\UnparseTagMentions::class),
+
+            (new Extend\Model(Post::class))
+                ->belongsToMany('mentionsTags', Tag::class, 'post_mentions_tag', 'post_id', 'mentions_tag_id'),
+
+            (new Extend\ApiSerializer(BasicPostSerializer::class))
+                ->hasMany('mentionsTags', TagSerializer::class),
+
+            (new Extend\ApiController(Controller\ShowDiscussionController::class))
+                ->load(['posts.mentionsTags']),
+
+            (new Extend\ApiController(Controller\ListDiscussionsController::class))
+                ->load([
+                    'firstPost.mentionsTags', 'lastPost.mentionsTags',
+                ]),
+
+            (new Extend\ApiController(Controller\ListPostsController::class))
+                ->load(['mentionsTags']),
+        ]),
 ];
--- a/extensions/mentions/js/src/@types/shims.d.ts
+++ b/extensions/mentions/js/src/@types/shims.d.ts
@@ -1,5 +1,18 @@
+import MentionFormats from '../forum/mentionables/formats/MentionFormats';
 import type BasePost from 'flarum/common/models/Post';

+declare module 'flarum/forum/ForumApplication' {
+  export default interface ForumApplication {
+    mentionFormats: MentionFormats;
+  }
+}
+
+declare module 'flarum/common/models/User' {
+  export default interface User {
+    canMentionGroups(): boolean;
+  }
+}
+
 declare module 'flarum/common/models/Post' {
  export default interface Post {
    mentionedBy(): BasePost[] | undefined | null;
--- a/extensions/mentions/js/src/forum/addComposerAutocomplete.js
+++ b/extensions/mentions/js/src/forum/addComposerAutocomplete.js
@@ -2,42 +2,15 @@ import app from 'flarum/forum/app';
 import { extend } from 'flarum/common/extend';
 import TextEditor from 'flarum/common/components/TextEditor';
 import TextEditorButton from 'flarum/common/components/TextEditorButton';
-import ReplyComposer from 'flarum/forum/components/ReplyComposer';
-import EditPostComposer from 'flarum/forum/components/EditPostComposer';
-import avatar from 'flarum/common/helpers/avatar';
-import usernameHelper from 'flarum/common/helpers/username';
-import highlight from 'flarum/common/helpers/highlight';
 import KeyboardNavigatable from 'flarum/common/utils/KeyboardNavigatable';
-import { truncate } from 'flarum/common/utils/string';
-import { throttle } from 'flarum/common/utils/throttleDebounce';
-import Badge from 'flarum/common/components/Badge';
-import Group from 'flarum/common/models/Group';

 import AutocompleteDropdown from './fragments/AutocompleteDropdown';
-import getMentionText from './utils/getMentionText';
-
-const throttledSearch = throttle(
-  250, // 250ms timeout
-  function (typed, searched, returnedUsers, returnedUserIds, dropdown, buildSuggestions) {
-    const typedLower = typed.toLowerCase();
-    if (!searched.includes(typedLower)) {
-      app.store.find('users', { filter: { q: typed }, page: { limit: 5 } }).then((results) => {
-        results.forEach((u) => {
-          if (!returnedUserIds.has(u.id())) {
-            returnedUserIds.add(u.id());
-            returnedUsers.push(u);
-          }
-        });
-
-        buildSuggestions();
-      });
-
-      searched.push(typedLower);
-    }
-  }
-);
+import MentionFormats from './mentionables/formats/MentionFormats';
+import MentionableModels from './mentionables/MentionableModels';

 export default function addComposerAutocomplete() {
+  app.mentionFormats = new MentionFormats();
+
  const $container = $('<div class="ComposerBody-mentionsDropdownContainer"></div>');
  const dropdown = new AutocompleteDropdown();

@@ -57,47 +30,42 @@ export default function addComposerAutocomplete() {
  });

  extend(TextEditor.prototype, 'buildEditorParams', function (params) {
-    const searched = [];
    let relMentionStart;
    let absMentionStart;
-    let typed;
    let matchTyped;

-    // We store users returned from an API here to preserve order in which they are returned
-    // This prevents the user list jumping around while users are returned.
-    // We also use a hashset for user IDs to provide O(1) lookup for the users already in the list.
-    const returnedUsers = Array.from(app.store.all('users'));
-    const returnedUserIds = new Set(returnedUsers.map((u) => u.id()));
+    let mentionables = new MentionableModels({
+      onmouseenter: function () {
+        dropdown.setIndex($(this).parent().index());
+      },
+      onclick: (replacement) => {
+        this.attrs.composer.editor.replaceBeforeCursor(absMentionStart - 1, replacement + ' ');

-    // Store groups, but exclude the two virtual groups - 'Guest' and 'Member'.
-    const returnedGroups = Array.from(
-      app.store.all('groups').filter((group) => {
-        return group.id() != Group.GUEST_ID && group.id() != Group.MEMBER_ID;
-      })
-    );
+        dropdown.hide();
+      },
+    });

-    const applySuggestion = (replacement) => {
-      this.attrs.composer.editor.replaceBeforeCursor(absMentionStart - 1, replacement + ' ');
-
-      dropdown.hide();
-    };
-
-    params.inputListeners.push(() => {
+    const suggestionsInputListener = () => {
      const selection = this.attrs.composer.editor.getSelectionRange();

      const cursor = selection[0];

      if (selection[1] - cursor > 0) return;

-      // Search backwards from the cursor for an '@' symbol. If we find one,
-      // we will want to show the autocomplete dropdown!
+      // Search backwards from the cursor for a mention triggering symbol. If we find one,
+      // we will want to show the correct autocomplete dropdown!
+      // Check classes implementing the IMentionableModel interface to see triggering symbols.
      const lastChunk = this.attrs.composer.editor.getLastNChars(30);
      absMentionStart = 0;
+      let activeFormat = null;
      for (let i = lastChunk.length - 1; i >= 0; i--) {
        const character = lastChunk.substr(i, 1);
-        if (character === '@' && (i == 0 || /\s/.test(lastChunk.substr(i - 1, 1)))) {
+        activeFormat = app.mentionFormats.get(character);
+
+        if (activeFormat && (i === 0 || /\s/.test(lastChunk.substr(i - 1, 1)))) {
          relMentionStart = i + 1;
          absMentionStart = cursor - lastChunk.length + i + 1;
+          mentionables.init(activeFormat.makeMentionables());
          break;
        }
      }
@@ -106,132 +74,14 @@ export default function addComposerAutocomplete() {
      dropdown.active = false;

      if (absMentionStart) {
-        typed = lastChunk.substring(relMentionStart).toLowerCase();
-        matchTyped = typed.match(/^["|“]((?:(?!"#).)+)$/);
-        typed = (matchTyped && matchTyped[1]) || typed;
-
-        const makeSuggestion = function (user, replacement, content, className = '') {
-          const username = usernameHelper(user);
-
-          if (typed) {
-            username.children = [highlight(username.text, typed)];
-            delete username.text;
-          }
-
-          return (
-            <button
-              className={'PostPreview ' + className}
-              onclick={() => applySuggestion(replacement)}
-              onmouseenter={function () {
-                dropdown.setIndex($(this).parent().index());
-              }}
-            >
-              <span className="PostPreview-content">
-                {avatar(user)}
-                {username} {content}
-              </span>
-            </button>
-          );
-        };
-
-        const makeGroupSuggestion = function (group, replacement, content, className = '') {
-          let groupName = group.namePlural().toLowerCase();
-
-          if (typed) {
-            groupName = highlight(groupName, typed);
-          }
-
-          return (
-            <button
-              className={'PostPreview ' + className}
-              onclick={() => applySuggestion(replacement)}
-              onmouseenter={function () {
-                dropdown.setIndex($(this).parent().index());
-              }}
-            >
-              <span className="PostPreview-content">
-                <Badge class={`Avatar Badge Badge--group--${group.id()} Badge-icon `} color={group.color()} type="group" icon={group.icon()} />
-                <span className="username">{groupName}</span>
-              </span>
-            </button>
-          );
-        };
-
-        const userMatches = function (user) {
-          const names = [user.username(), user.displayName()];
-
-          return names.some((name) => name.toLowerCase().substr(0, typed.length) === typed);
-        };
-
-        const groupMatches = function (group) {
-          const names = [group.nameSingular(), group.namePlural()];
-
-          return names.some((name) => name.toLowerCase().substr(0, typed.length) === typed);
-        };
+        const typed = lastChunk.substring(relMentionStart).toLowerCase();
+        matchTyped = activeFormat.queryFromTyped(typed);
+        mentionables.typed = matchTyped || typed;

        const buildSuggestions = () => {
-          const suggestions = [];
-
-          // If the user has started to type a username, then suggest users
-          // matching that username.
-          if (typed) {
-            returnedUsers.forEach((user) => {
-              if (!userMatches(user)) return;
-
-              suggestions.push(makeSuggestion(user, getMentionText(user), '', 'MentionsDropdown-user'));
-            });
-
-            // ... or groups.
-            if (app.session?.user?.canMentionGroups()) {
-              returnedGroups.forEach((group) => {
-                if (!groupMatches(group)) return;
-
-                suggestions.push(makeGroupSuggestion(group, getMentionText(undefined, undefined, group), '', 'MentionsDropdown-group'));
-              });
-            }
-          }
-
-          // If the user is replying to a discussion, or if they are editing a
-          // post, then we can suggest other posts in the discussion to mention.
-          // We will add the 5 most recent comments in the discussion which
-          // match any username characters that have been typed.
-          if (this.attrs.composer.bodyMatches(ReplyComposer) || this.attrs.composer.bodyMatches(EditPostComposer)) {
-            const composerAttrs = this.attrs.composer.body.attrs;
-            const composerPost = composerAttrs.post;
-            const discussion = (composerPost && composerPost.discussion()) || composerAttrs.discussion;
-
-            if (discussion) {
-              discussion
-                .posts()
-                // Filter to only comment posts, and replies before this message
-                .filter((post) => post && post.contentType() === 'comment' && (!composerPost || post.number() < composerPost.number()))
-                // Sort by new to old
-                .sort((a, b) => b.createdAt() - a.createdAt())
-                // Filter to where the user matches what is being typed
-                .filter((post) => {
-                  const user = post.user();
-                  return user && userMatches(user);
-                })
-                // Get the first 5
-                .splice(0, 5)
-                // Make the suggestions
-                .forEach((post) => {
-                  const user = post.user();
-                  suggestions.push(
-                    makeSuggestion(
-                      user,
-                      getMentionText(user, post.id()),
-                      [
-                        app.translator.trans('flarum-mentions.forum.composer.reply_to_post_text', { number: post.number() }),
-                        ' — ',
-                        truncate(post.contentPlain(), 200),
-                      ],
-                      'MentionsDropdown-post'
-                    )
-                  );
-                });
-            }
-          }
+          // If the user has started to type a mention,
+          // then suggest models matching.
+          const suggestions = mentionables.buildSuggestions();

          if (suggestions.length) {
            dropdown.items = suggestions;
@@ -271,13 +121,11 @@ export default function addComposerAutocomplete() {
        dropdown.setIndex(0);
        dropdown.$().scrollTop(0);

-        // Don't send API calls searching for users until at least 2 characters have been typed.
-        // This focuses the mention results on users and posts in the discussion.
-        if (typed.length > 1 && app.forum.attribute('canSearchUsers')) {
-          throttledSearch(typed, searched, returnedUsers, returnedUserIds, dropdown, buildSuggestions);
-        }
+        mentionables.search()?.then(buildSuggestions);
      }
-    });
+    };
+
+    params.inputListeners.push(suggestionsInputListener);
  });

  extend(TextEditor.prototype, 'toolbarItems', function (items) {
--- a/extensions/mentions/js/src/forum/addPostMentionPreviews.js
+++ b/extensions/mentions/js/src/forum/addPostMentionPreviews.js
@@ -14,10 +14,14 @@ export default function addPostMentionPreviews() {
    const parentPost = this.attrs.post;
    const $parentPost = this.$();

-    this.$().on('click', '.UserMention:not(.UserMention--deleted), .PostMention:not(.PostMention--deleted)', function (e) {
-      m.route.set(this.getAttribute('href'));
-      e.preventDefault();
-    });
+    this.$().on(
+      'click',
+      '.UserMention:not(.UserMention--deleted), .PostMention:not(.PostMention--deleted), .TagMention:not(.TagMention--deleted)',
+      function (e) {
+        m.route.set(this.getAttribute('href'));
+        e.preventDefault();
+      }
+    );

    this.$('.PostMention:not(.PostMention--deleted)').each(function () {
      const $this = $(this);
--- a/extensions/mentions/js/src/forum/compat.js
+++ b/extensions/mentions/js/src/forum/compat.js
@@ -9,6 +9,9 @@ import getMentionText from './utils/getMentionText';
 import * as reply from './utils/reply';
 import selectedText from './utils/selectedText';
 import * as textFormatter from './utils/textFormatter';
+import MentionableModel from './mentionables/MentionableModel';
+import MentionFormat from './mentionables/formats/MentionFormat';
+import Mentionables from './extenders/Mentionables';

 export default {
  'mentions/components/MentionsUserPage': MentionsUserPage,
@@ -22,4 +25,7 @@ export default {
  'mentions/utils/reply': reply,
  'mentions/utils/selectedText': selectedText,
  'mentions/utils/textFormatter': textFormatter,
+  'mentions/mentionables/MentionableModel': MentionableModel,
+  'mentions/mentionables/formats/MentionFormat': MentionFormat,
+  'mentions/extenders/Mentionables': Mentionables,
 };
--- a/extensions/mentions/js/src/forum/components/MentionsDropdownItem.tsx
+++ b/extensions/mentions/js/src/forum/components/MentionsDropdownItem.tsx
@@ -0,0 +1,25 @@
+import Component from 'flarum/common/Component';
+import type { ComponentAttrs } from 'flarum/common/Component';
+import classList from 'flarum/common/utils/classList';
+import type MentionableModel from '../mentionables/MentionableModel';
+import type Mithril from 'mithril';
+
+export interface IMentionsDropdownItemAttrs extends ComponentAttrs {
+  mentionable: MentionableModel;
+  onclick: () => void;
+  onmouseenter: () => void;
+}
+
+export default class MentionsDropdownItem<CustomAttrs extends IMentionsDropdownItemAttrs> extends Component<CustomAttrs> {
+  view(vnode: Mithril.Vnode<CustomAttrs>): Mithril.Children {
+    const { mentionable, ...attrs } = this.attrs;
+
+    const className = classList('MentionsDropdownItem', 'PostPreview', `MentionsDropdown-${mentionable.type()}`);
+
+    return (
+      <button className={className} {...attrs}>
+        <span className="PostPreview-content">{vnode.children}</span>
+      </button>
+    );
+  }
+}
--- a/extensions/mentions/js/src/forum/extenders/Mentionables.ts
+++ b/extensions/mentions/js/src/forum/extenders/Mentionables.ts
@@ -0,0 +1,54 @@
+import type ForumApplication from 'flarum/forum/ForumApplication';
+import type IExtender from 'flarum/common/extenders/IExtender';
+import type MentionableModel from '../mentionables/MentionableModel';
+import type MentionFormat from '../mentionables/formats/MentionFormat';
+
+export default class Mentionables implements IExtender<ForumApplication> {
+  protected formats: (new () => MentionFormat)[] = [];
+  protected mentionables: Record<string, (new () => MentionableModel)[]> = {};
+
+  /**
+   * Register a new mention format.
+   * Must extend MentionFormat and have a unique unused trigger symbol.
+   */
+  format(format: new () => MentionFormat): this {
+    this.formats.push(format);
+
+    return this;
+  }
+
+  /**
+   * Register a new mentionable model to a mention format.
+   * Only works if the format has already been registered,
+   *  and the format allows using multiple mentionables.
+   *
+   * @param symbol The trigger symbol of the format to extend (ex: @).
+   * @param mentionable The mentionable instance to register.
+   *                    Must extend MentionableModel.
+   */
+  mentionable(symbol: string, mentionable: new () => MentionableModel): this {
+    if (!this.mentionables[symbol]) {
+      this.mentionables[symbol] = [];
+    }
+
+    this.mentionables[symbol].push(mentionable);
+
+    return this;
+  }
+
+  extend(app: ForumApplication): void {
+    for (const format of this.formats) {
+      app.mentionFormats.extend(format);
+    }
+
+    for (const symbol in this.mentionables) {
+      const format = app.mentionFormats.get(symbol);
+
+      if (!format) continue;
+
+      for (const mentionable of this.mentionables[symbol]) {
+        format.extend(mentionable);
+      }
+    }
+  }
+}
--- a/extensions/mentions/js/src/forum/index.js
+++ b/extensions/mentions/js/src/forum/index.js
@@ -87,8 +87,8 @@ app.initializers.add('flarum-mentions', function () {

  // Apply color contrast fix on group mentions.
  extend(Post.prototype, 'oncreate', function () {
-    this.$('.GroupMention--colored').each(function () {
-      this.classList.add(textContrastClass(getComputedStyle(this).getPropertyValue('--group-color')));
+    this.$('.GroupMention--colored, .TagMention--colored').each(function () {
+      this.classList.add(textContrastClass(getComputedStyle(this).getPropertyValue('--color')));
    });
  });
 });
--- a/extensions/mentions/js/src/forum/mentionables/GroupMention.tsx
+++ b/extensions/mentions/js/src/forum/mentionables/GroupMention.tsx
@@ -0,0 +1,72 @@
+import app from 'flarum/forum/app';
+import Group from 'flarum/common/models/Group';
+import MentionableModel from './MentionableModel';
+import type Mithril from 'mithril';
+import Badge from 'flarum/common/components/Badge';
+import highlight from 'flarum/common/helpers/highlight';
+import type AtMentionFormat from './formats/AtMentionFormat';
+
+export default class GroupMention extends MentionableModel<Group, AtMentionFormat> {
+  type(): string {
+    return 'group';
+  }
+
+  initialResults(): Group[] {
+    return Array.from(
+      app.store.all<Group>('groups').filter((g: Group) => {
+        return g.id() !== Group.GUEST_ID && g.id() !== Group.MEMBER_ID;
+      })
+    );
+  }
+
+  /**
+   * Generates the mention syntax for a group mention.
+   *
+   * @"Name Plural"#gGroupID
+   *
+   * @example <caption>Group mention</caption>
+   * // '@"Mods"#g4'
+   * forGroup(group) // Group display name is 'Mods', group ID is 4
+   */
+  public replacement(group: Group): string {
+    return this.format.format(group.namePlural(), 'g', group.id());
+  }
+
+  suggestion(model: Group, typed: string): Mithril.Children {
+    let groupName: Mithril.Children = model.namePlural();
+
+    if (typed) {
+      groupName = highlight(groupName, typed);
+    }
+
+    return (
+      <>
+        <Badge className={`Avatar Badge Badge--group--${model.id()} Badge-icon`} color={model.color()} type="group" icon={model.icon()} />
+        <span className="username">{groupName}</span>
+      </>
+    );
+  }
+
+  matches(model: Group, typed: string): boolean {
+    if (!typed) return false;
+
+    const names = [model.namePlural().toLowerCase(), model.nameSingular().toLowerCase()];
+
+    return names.some((name) => name.toLowerCase().substr(0, typed.length) === typed);
+  }
+
+  maxStoreMatchedResults(): null {
+    return null;
+  }
+
+  /**
+   * All groups are already loaded, so we don't need to search for them.
+   */
+  search(typed: string): Promise<Group[]> {
+    return Promise.resolve([]);
+  }
+
+  enabled(): boolean {
+    return app.session?.user?.canMentionGroups() ?? false;
+  }
+}
--- a/extensions/mentions/js/src/forum/mentionables/MentionableModel.ts
+++ b/extensions/mentions/js/src/forum/mentionables/MentionableModel.ts
@@ -0,0 +1,20 @@
+import type Mithril from 'mithril';
+import type Model from 'flarum/common/Model';
+import type MentionFormat from './formats/MentionFormat';
+
+export default abstract class MentionableModel<M extends Model = Model, Format extends MentionFormat = MentionFormat> {
+  public format: Format;
+
+  public constructor(format: Format) {
+    this.format = format;
+  }
+
+  abstract type(): string;
+  abstract initialResults(): M[];
+  abstract search(typed: string): Promise<M[]>;
+  abstract replacement(model: M): string;
+  abstract suggestion(model: M, typed: string): Mithril.Children;
+  abstract matches(model: M, typed: string): boolean;
+  abstract maxStoreMatchedResults(): number | null;
+  abstract enabled(): boolean;
+}
--- a/extensions/mentions/js/src/forum/mentionables/MentionableModels.tsx
+++ b/extensions/mentions/js/src/forum/mentionables/MentionableModels.tsx
@@ -0,0 +1,93 @@
+import MentionFormats from './MentionFormats';
+import type MentionableModel from './MentionableModel';
+import type Model from 'flarum/common/Model';
+import type Mithril from 'mithril';
+import MentionsDropdownItem from '../components/MentionsDropdownItem';
+import { throttle } from 'flarum/common/utils/throttleDebounce';
+
+export default class MentionableModels {
+  protected mentionables?: MentionableModel[];
+  /**
+   * We store models returned from an API here to preserve order in which they are returned
+   * This prevents the list jumping around while models are returned.
+   * We also use a hashmap for model IDs to provide O(1) lookup for the users already in the list.
+   */
+  private results: Record<string, Map<string, Model>> = {};
+  public typed: string | null = null;
+  private searched: string[] = [];
+  private dropdownItemAttrs: Record<string, any> = {};
+
+  constructor(dropdownItemAttrs: Record<string, any>) {
+    this.dropdownItemAttrs = dropdownItemAttrs;
+  }
+
+  public init(mentionables: MentionableModel[]): void {
+    this.typed = null;
+    this.mentionables = mentionables;
+
+    for (const mentionable of this.mentionables) {
+      this.results[mentionable.type()] = new Map(mentionable.initialResults().map((result) => [result.id() as string, result]));
+    }
+  }
+
+  /**
+   * Don't send API calls searching for models until at least 2 characters have been typed.
+   * This focuses the mention results on models already loaded.
+   */
+  public readonly search = throttle(250, async (): Promise<void> => {
+    if (!this.typed || this.typed.length <= 1) return;
+
+    const typedLower = this.typed.toLowerCase();
+
+    if (this.searched.includes(typedLower)) return;
+
+    for (const mentionable of this.mentionables!) {
+      for (const model of await mentionable.search(typedLower)) {
+        if (!this.results[mentionable.type()].has(model.id() as string)) {
+          this.results[mentionable.type()].set(model.id() as string, model);
+        }
+      }
+    }
+
+    this.searched.push(typedLower);
+
+    return Promise.resolve();
+  });
+
+  public matches(mentionable: MentionableModel, model: Model): boolean {
+    return mentionable.matches(model, this.typed?.toLowerCase() || '');
+  }
+
+  public makeSuggestion(mentionable: MentionableModel, model: Model): Mithril.Children {
+    const content = mentionable.suggestion(model, this.typed!);
+    const replacement = mentionable.replacement(model);
+
+    const { onclick, ...attrs } = this.dropdownItemAttrs;
+
+    return (
+      <MentionsDropdownItem mentionable={mentionable} onclick={() => onclick(replacement)} {...attrs}>
+        {content}
+      </MentionsDropdownItem>
+    );
+  }
+
+  public buildSuggestions(): Mithril.Children {
+    const suggestions: Mithril.Children = [];
+
+    for (const mentionable of this.mentionables!) {
+      if (!mentionable.enabled()) continue;
+
+      let matches = Array.from(this.results[mentionable.type()].values()).filter((model) => this.matches(mentionable, model));
+
+      const max = mentionable.maxStoreMatchedResults();
+      if (max) matches = matches.splice(0, max);
+
+      for (const model of matches) {
+        const dropdownItem = this.makeSuggestion(mentionable, model);
+        suggestions.push(dropdownItem);
+      }
+    }
+
+    return suggestions;
+  }
+}
--- a/extensions/mentions/js/src/forum/mentionables/PostMention.tsx
+++ b/extensions/mentions/js/src/forum/mentionables/PostMention.tsx
@@ -0,0 +1,102 @@
+import app from 'flarum/forum/app';
+import MentionableModel from './MentionableModel';
+import type Post from 'flarum/common/models/Post';
+import type Mithril from 'mithril';
+import usernameHelper from 'flarum/common/helpers/username';
+import avatar from 'flarum/common/helpers/avatar';
+import highlight from 'flarum/common/helpers/highlight';
+import { truncate } from 'flarum/common/utils/string';
+import ReplyComposer from 'flarum/forum/components/ReplyComposer';
+import EditPostComposer from 'flarum/forum/components/EditPostComposer';
+import getCleanDisplayName from '../utils/getCleanDisplayName';
+import type AtMentionFormat from './formats/AtMentionFormat';
+
+export default class PostMention extends MentionableModel<Post, AtMentionFormat> {
+  type(): string {
+    return 'post';
+  }
+
+  /**
+   * If the user is replying to a discussion, or if they are editing a
+   * post, then we can suggest other posts in the discussion to mention.
+   * We will add the 5 most recent comments in the discussion which
+   * match any username characters that have been typed.
+   */
+  initialResults(): Post[] {
+    if (!app.composer.bodyMatches(ReplyComposer) && !app.composer.bodyMatches(EditPostComposer)) {
+      return [];
+    }
+
+    // @ts-ignore
+    const composerAttrs = app.composer.body.attrs;
+    const composerPost = composerAttrs.post;
+    const discussion = (composerPost && composerPost.discussion()) || composerAttrs.discussion;
+
+    return (
+      discussion
+        .posts()
+        // Filter to only comment posts, and replies before this message
+        .filter((post: Post) => post && post.contentType() === 'comment' && (!composerPost || post.number() < composerPost.number()))
+        // Sort by new to old
+        .sort((a: Post, b: Post) => b.createdAt().getTime() - a.createdAt().getTime())
+    );
+  }
+
+  /**
+   * Generates the syntax for mentioning of a post. Also cleans up the display name.
+   *
+   * @example <caption>Post mention</caption>
+   * // '@"User"#p13'
+   * // @"Display name"#pPostID
+   * forPostMention(user, 13) // User display name is 'User', post ID is 13
+   */
+  public replacement(post: Post): string {
+    const user = post.user();
+    const cleanText = getCleanDisplayName(user);
+    return this.format.format(cleanText, 'p', post.id());
+  }
+
+  suggestion(model: Post, typed: string): Mithril.Children {
+    const user = model.user() || null;
+    const username = usernameHelper(user);
+
+    if (typed) {
+      username.children = [highlight((username.text ?? '') as string, typed)];
+      delete username.text;
+    }
+
+    return (
+      <>
+        {avatar(user)}
+        {username}
+        {[
+          app.translator.trans('flarum-mentions.forum.composer.reply_to_post_text', { number: model.number() }),
+          ' — ',
+          truncate(model.contentPlain() ?? '', 200),
+        ]}
+      </>
+    );
+  }
+
+  matches(model: Post, typed: string): boolean {
+    const user = model.user();
+    const userMentionable = app.mentionFormats.mentionable('user')!;
+
+    return !typed || (user && userMentionable.matches(user, typed));
+  }
+
+  maxStoreMatchedResults(): number {
+    return 5;
+  }
+
+  /**
+   * Post mention suggestions are only offered from current discussion posts.
+   */
+  search(typed: string): Promise<Post[]> {
+    return Promise.resolve([]);
+  }
+
+  enabled(): boolean {
+    return true;
+  }
+}
--- a/extensions/mentions/js/src/forum/mentionables/TagMention.tsx
+++ b/extensions/mentions/js/src/forum/mentionables/TagMention.tsx
@@ -0,0 +1,65 @@
+import app from 'flarum/forum/app';
+import Badge from 'flarum/common/components/Badge';
+import highlight from 'flarum/common/helpers/highlight';
+import type Tag from 'flarum/tags/common/models/Tag';
+import type Mithril from 'mithril';
+import MentionableModel from './MentionableModel';
+import type HashMentionFormat from './formats/HashMentionFormat';
+
+export default class TagMention extends MentionableModel<Tag, HashMentionFormat> {
+  type(): string {
+    return 'tag';
+  }
+
+  initialResults(): Tag[] {
+    return Array.from(app.store.all<Tag>('tags'));
+  }
+
+  /**
+   * Generates the mention syntax for a tag mention.
+   *
+   * ~tagSlug
+   *
+   * @example <caption>Tag mention</caption>
+   * // ~general
+   * forTag(tag) // Tag display name is 'Tag', tag ID is 5
+   */
+  public replacement(tag: Tag): string {
+    return this.format.format(tag.slug());
+  }
+
+  matches(model: Tag, typed: string): boolean {
+    if (!typed) return false;
+
+    const names = [model.name().toLowerCase()];
+
+    return names.some((name) => name.toLowerCase().substr(0, typed.length) === typed);
+  }
+
+  maxStoreMatchedResults(): null {
+    return null;
+  }
+
+  async search(typed: string): Promise<Tag[]> {
+    return await app.store.find<Tag[]>('tags', { filter: { q: typed }, page: { limit: 5 } });
+  }
+
+  suggestion(model: Tag, typed: string): Mithril.Children {
+    let tagName: Mithril.Children = model.name();
+
+    if (typed) {
+      tagName = highlight(tagName, typed);
+    }
+
+    return (
+      <>
+        <Badge className="Avatar" icon={model.icon()} color={model.color()} type="tag" />
+        <span className="username">{tagName}</span>
+      </>
+    );
+  }
+
+  enabled(): boolean {
+    return 'flarum-tags' in flarum.extensions;
+  }
+}
--- a/extensions/mentions/js/src/forum/mentionables/UserMention.tsx
+++ b/extensions/mentions/js/src/forum/mentionables/UserMention.tsx
@@ -0,0 +1,79 @@
+import app from 'flarum/forum/app';
+import type Mithril from 'mithril';
+import type User from 'flarum/common/models/User';
+import usernameHelper from 'flarum/common/helpers/username';
+import avatar from 'flarum/common/helpers/avatar';
+import highlight from 'flarum/common/helpers/highlight';
+import MentionableModel from './MentionableModel';
+import getCleanDisplayName, { shouldUseOldFormat } from '../utils/getCleanDisplayName';
+import AtMentionFormat from './formats/AtMentionFormat';
+
+export default class UserMention extends MentionableModel<User, AtMentionFormat> {
+  type(): string {
+    return 'user';
+  }
+
+  initialResults(): User[] {
+    return Array.from(app.store.all<User>('users'));
+  }
+
+  /**
+   * Automatically determines which mention syntax to be used based on the option in the
+   * admin dashboard. Also performs display name clean-up automatically.
+   *
+   * @"Display name"#UserID or `@username`
+   *
+   * @example <caption>New display name syntax</caption>
+   * // '@"user"#1'
+   * forUser(User) // User is ID 1, display name is 'User'
+   *
+   * @example <caption>Using old syntax</caption>
+   * // '@username'
+   * forUser(user) // User's username is 'username'
+   */
+  public replacement(user: User): string {
+    if (shouldUseOldFormat()) {
+      const cleanText = getCleanDisplayName(user, false);
+      return this.format.format(cleanText);
+    }
+
+    const cleanText = getCleanDisplayName(user);
+    return this.format.format(cleanText, '', user.id());
+  }
+
+  suggestion(model: User, typed: string): Mithril.Children {
+    const username = usernameHelper(model);
+
+    if (typed) {
+      username.children = [highlight((username.text ?? '') as string, typed)];
+      delete username.text;
+    }
+
+    return (
+      <>
+        {avatar(model)}
+        {username}
+      </>
+    );
+  }
+
+  matches(model: User, typed: string): boolean {
+    if (!typed) return false;
+
+    const names = [model.username(), model.displayName()];
+
+    return names.some((name) => name.toLowerCase().substr(0, typed.length) === typed);
+  }
+
+  maxStoreMatchedResults(): null {
+    return null;
+  }
+
+  async search(typed: string): Promise<User[]> {
+    return await app.store.find<User[]>('users', { filter: { q: typed }, page: { limit: 5 } });
+  }
+
+  enabled(): boolean {
+    return true;
+  }
+}
--- a/extensions/mentions/js/src/forum/mentionables/formats/AtMentionFormat.ts
+++ b/extensions/mentions/js/src/forum/mentionables/formats/AtMentionFormat.ts
@@ -0,0 +1,27 @@
+import MentionFormat from './MentionFormat';
+import type MentionableModel from '../MentionableModel';
+import UserMention from '../UserMention';
+import PostMention from '../PostMention';
+import GroupMention from '../GroupMention';
+
+export default class AtMentionFormat extends MentionFormat {
+  public mentionables: (new (...args: any[]) => MentionableModel)[] = [UserMention, PostMention, GroupMention];
+  protected extendable: boolean = true;
+
+  public trigger(): string {
+    return '@';
+  }
+
+  public queryFromTyped(typed: string): string | null {
+    const matchTyped = typed.match(/^["“]((?:(?!"#).)+)$/);
+
+    return matchTyped ? matchTyped[1] : null;
+  }
+
+  public format(name: string, char: string | null = '', id: string | null = null): string {
+    return {
+      simple: `@${name}`,
+      safe: `@"${name}"#${char}${id}`,
+    }[id ? 'safe' : 'simple'];
+  }
+}
--- a/extensions/mentions/js/src/forum/mentionables/formats/HashMentionFormat.ts
+++ b/extensions/mentions/js/src/forum/mentionables/formats/HashMentionFormat.ts
@@ -0,0 +1,22 @@
+import MentionFormat from './MentionFormat';
+import MentionableModel from '../MentionableModel';
+import TagMention from '../TagMention';
+
+export default class HashMentionFormat extends MentionFormat {
+  public mentionables: (new (...args: any[]) => MentionableModel)[] = [TagMention];
+  protected extendable: boolean = false;
+
+  public trigger(): string {
+    return '#';
+  }
+
+  public queryFromTyped(typed: string): string | null {
+    const matchTyped = typed.match(/^[-_\p{L}\p{N}\p{M}]+$/giu);
+
+    return matchTyped ? matchTyped[1] : null;
+  }
+
+  public format(slug: string): string {
+    return `#${slug}`;
+  }
+}
--- a/extensions/mentions/js/src/forum/mentionables/formats/MentionFormat.ts
+++ b/extensions/mentions/js/src/forum/mentionables/formats/MentionFormat.ts
@@ -0,0 +1,26 @@
+import type MentionableModel from '../MentionableModel';
+import type Model from 'flarum/common/Model';
+
+export default abstract class MentionFormat {
+  protected instances?: MentionableModel[];
+
+  public makeMentionables(): MentionableModel[] {
+    return this.instances ?? (this.instances = this.mentionables.map((Mentionable) => new Mentionable(this)));
+  }
+
+  public getMentionable(type: string): MentionableModel | null {
+    return this.makeMentionables().find((mentionable) => mentionable.type() === type) ?? null;
+  }
+
+  public extend(mentionable: new (...args: any[]) => MentionableModel): void {
+    if (!this.extendable) throw new Error('This mention format does not allow extending.');
+
+    this.mentionables.push(mentionable);
+  }
+
+  abstract mentionables: (new (...args: any[]) => MentionableModel)[];
+  protected abstract extendable: boolean;
+  abstract trigger(): string;
+  abstract queryFromTyped(typed: string): string | null;
+  abstract format(...args: any): string;
+}
--- a/extensions/mentions/js/src/forum/mentionables/formats/MentionFormats.ts
+++ b/extensions/mentions/js/src/forum/mentionables/formats/MentionFormats.ts
@@ -0,0 +1,26 @@
+import AtMentionFormat from './AtMentionFormat';
+import HashMentionFormat from './HashMentionFormat';
+import type MentionFormat from './MentionFormat';
+import MentionableModel from '../MentionableModel';
+
+export default class MentionFormats {
+  protected formats: MentionFormat[] = [new AtMentionFormat(), new HashMentionFormat()];
+
+  public get(symbol: string): MentionFormat | null {
+    return this.formats.find((f) => f.trigger() === symbol) ?? null;
+  }
+
+  public mentionable(type: string): MentionableModel | null {
+    for (const format of this.formats) {
+      const mentionable = format.getMentionable(type);
+
+      if (mentionable) return mentionable;
+    }
+
+    return null;
+  }
+
+  public extend(format: new () => MentionFormat) {
+    this.formats.push(new format());
+  }
+}
--- a/extensions/mentions/js/src/forum/utils/getMentionText.js
+++ b/extensions/mentions/js/src/forum/utils/getMentionText.js
@@ -1,45 +1,21 @@
-import getCleanDisplayName, { shouldUseOldFormat } from './getCleanDisplayName';
+import app from 'flarum/forum/app';

 /**
- * Fetches the mention text for a specified user (and optionally a post ID for replies, or group).
+ * Fetches the mention text for a specified user (and optionally a post ID for replies or group).
 *
 * Automatically determines which mention syntax to be used based on the option in the
 * admin dashboard. Also performs display name clean-up automatically.
 *
- * @example <caption>New display name syntax</caption>
- * // '@"User"#1'
- * getMentionText(User) // User is ID 1, display name is 'User'
- *
- * @example <caption>Replying</caption>
- * // '@"User"#p13'
- * getMentionText(User, 13) // User display name is 'User', post ID is 13
- *
- * @example <caption>Using old syntax</caption>
- * // '@username'
- * getMentionText(User) // User's username is 'username'
- *
- * @example <caption>Group mention</caption>
- * // '@"Mods"#g4'
- * getMentionText(undefined, undefined, group) // Group display name is 'Mods', group ID is 4
+ * @deprecated Use `app.mentionables.get('user').replacement(user)` instead. Will be removed in 2.0.
 */
 export default function getMentionText(user, postId, group) {
  if (user !== undefined && postId === undefined) {
-    if (shouldUseOldFormat()) {
-      // Plain @username
-      const cleanText = getCleanDisplayName(user, false);
-      return `@${cleanText}`;
-    }
-    // @"Display name"#UserID
-    const cleanText = getCleanDisplayName(user);
-    return `@"${cleanText}"#${user.id()}`;
+    return app.mentionables.get('user').replacement(user);
  } else if (user !== undefined && postId !== undefined) {
-    // @"Display name"#pPostID
-    const cleanText = getCleanDisplayName(user);
-    return `@"${cleanText}"#p${postId}`;
+    return app.mentionables.get('post').replacement(app.store.getById('posts', postId));
  } else if (group !== undefined) {
-    // @"Name Plural"#gGroupID
-    return `@"${group.namePlural()}"#g${group.id()}`;
-  } else {
-    throw 'No parameters were passed';
+    return app.mentionables.get('group').replacement(group);
  }
+
+  throw 'No parameters were passed';
 }
--- a/extensions/mentions/js/src/forum/utils/reply.js
+++ b/extensions/mentions/js/src/forum/utils/reply.js
@@ -1,12 +1,10 @@
 import app from 'flarum/forum/app';
 import DiscussionControls from 'flarum/forum/utils/DiscussionControls';
 import EditPostComposer from 'flarum/forum/components/EditPostComposer';
-import getMentionText from './getMentionText';

 export function insertMention(post, composer, quote) {
  return new Promise((resolve) => {
-    const user = post.user();
-    const mention = getMentionText(user, post.id()) + ' ';
+    const mention = app.mentionFormats.mentionable('post').replacement(post) + ' ';

    // If the composer is empty, then assume we're starting a new reply.
    // In which case we don't want the user to have to confirm if they
--- a/extensions/mentions/js/src/forum/utils/textFormatter.js
+++ b/extensions/mentions/js/src/forum/utils/textFormatter.js
@@ -20,6 +20,10 @@ export function filterUserMentions(tag) {
  tag.invalidate();
 }

+export function postFilterUserMentions(tag) {
+  tag.setAttribute('deleted', false);
+}
+
 export function filterPostMentions(tag) {
  const post = app.store.getById('posts', tag.getAttribute('id'));

@@ -32,14 +36,16 @@ export function filterPostMentions(tag) {
  }
 }

+export function postFilterPostMentions(tag) {
+  tag.setAttribute('deleted', false);
+}
+
 export function filterGroupMentions(tag) {
  if (app.session?.user?.canMentionGroups()) {
    const group = app.store.getById('groups', tag.getAttribute('id'));

    if (group) {
      tag.setAttribute('groupname', extractText(group.namePlural()));
-      tag.setAttribute('icon', group.icon());
-      tag.setAttribute('color', group.color());

      return true;
    }
@@ -47,3 +53,38 @@ export function filterGroupMentions(tag) {

  tag.invalidate();
 }
+
+export function postFilterGroupMentions(tag) {
+  if (app.session?.user?.canMentionGroups()) {
+    const group = app.store.getById('groups', tag.getAttribute('id'));
+
+    tag.setAttribute('color', group.color());
+    tag.setAttribute('icon', group.icon());
+    tag.setAttribute('deleted', false);
+  }
+}
+
+export function filterTagMentions(tag) {
+  if ('flarum-tags' in flarum.extensions) {
+    const model = app.store.getBy('tags', 'slug', tag.getAttribute('slug'));
+
+    if (model) {
+      tag.setAttribute('id', model.id());
+      tag.setAttribute('tagname', model.name());
+
+      return true;
+    }
+  }
+
+  tag.invalidate();
+}
+
+export function postFilterTagMentions(tag) {
+  if ('flarum-tags' in flarum.extensions) {
+    const model = app.store.getBy('tags', 'slug', tag.getAttribute('slug'));
+
+    tag.setAttribute('icon', model.icon());
+    tag.setAttribute('color', model.color());
+    tag.setAttribute('deleted', false);
+  }
+}
--- a/extensions/mentions/js/tsconfig.json
+++ b/extensions/mentions/js/tsconfig.json
@@ -10,6 +10,7 @@
    "declarationDir": "./dist-typings",
    "paths": {
      "flarum/*": ["../../../framework/core/js/dist-typings/*"],
+      "flarum/tags/*": ["../../tags/js/dist-typings/*"],
      // TODO: remove after export registry system implemented
      // Without this, the old-style `@flarum/core` import is resolved to
      // source code in flarum/core instead of the dist typings.
--- a/extensions/mentions/less/forum.less
+++ b/extensions/mentions/less/forum.less
@@ -2,8 +2,6 @@
  background: var(--control-bg);
  color: var(--control-color);
  border-radius: @border-radius;
-  padding: 2px 5px;
-  border: 0 !important;
  font-weight: 600;

  blockquote & {
@@ -14,7 +12,12 @@
    color: var(--link-color);
  }
 }
-.UserMention, .PostMention, .GroupMention {
+.UserMention, .PostMention, .GroupMention, .TagMention {
+  padding: 2px 5px;
+  vertical-align: middle;
+  border: 0 !important;
+  white-space: nowrap;
+
  &--deleted {
    opacity: 0.8;
    filter: grayscale(1);
@@ -27,12 +30,38 @@
    margin-left: 0;
  }

+  // @TODO: 2.0 use an icon in the XSLT template.
  &:before {
    .fas();
    content: @fa-var-reply;
    margin-right: 5px;
  }
 }
+.GroupMention {
+  background-color: var(--color, var(--control-bg));
+  color: var(--control-color);
+  --link-color: currentColor;
+
+  &--colored {
+    --control-color: var(--contrast-color, var(--body-bg));
+    --link-color: var(--control-color);
+  }
+
+  .icon {
+    margin-left: 5px;
+  }
+}
+& when (is-extension-enabled('flarum-tags')) {
+  .TagMention {
+    --tag-bg: var(--color, var(--control-bg));
+    .tag-label();
+    margin: 0 2px;
+
+    .icon {
+      margin-right: 2px;
+    }
+  }
+}
 .ComposerBody-mentionsWrapper {
  position: relative;
 }
@@ -50,6 +79,7 @@
  }
 }
 .MentionsDropdown, .PostMention-preview, .Post-mentionedBy-preview {
+  // @TODO: Rename to .MentionsDropdownItem, along with child classes. 2.0
  .PostPreview {
    color: @muted-color;

@@ -97,24 +127,9 @@
  position: absolute;
  .Button--color(@tooltip-color, @tooltip-bg);
 }
-.GroupMention {
-  background-color: var(--group-color, var(--control-bg));
-  color: var(--control-color);
-  --link-color: currentColor;
-
-  &--colored {
-    --control-color: var(--contrast-color, var(--body-bg));
-    --link-color: var(--control-color);
-  }
-
-  .icon {
-    margin-left: 5px;
-  }
-}
 .MentionsDropdown .Badge {
  box-shadow: none;
 }
-
@media @phone {
  .MentionsDropdown {
    max-width: 100%;
--- a/extensions/mentions/src/ConfigureMentions.php
+++ b/extensions/mentions/src/ConfigureMentions.php
@@ -9,14 +9,21 @@

 namespace Flarum\Mentions;

+use Flarum\Extension\ExtensionManager;
 use Flarum\Group\Group;
+use Flarum\Group\GroupRepository;
 use Flarum\Http\UrlGenerator;
 use Flarum\Post\PostRepository;
 use Flarum\Settings\SettingsRepositoryInterface;
+use Flarum\Tags\Tag;
+use Flarum\Tags\TagRepository;
 use Flarum\User\User;
 use s9e\TextFormatter\Configurator;
-use s9e\TextFormatter\Parser\Tag;
+use s9e\TextFormatter\Parser\Tag as FormatterTag;

+/**
+ * @TODO: refactor this lump of code into a mentionable models polymorphic system (for v2.0).
+ */
 class ConfigureMentions
 {
    /**
@@ -25,11 +32,14 @@ class ConfigureMentions
    protected $url;

    /**
-     * @param UrlGenerator $url
+     * @var ExtensionManager
     */
-    public function __construct(UrlGenerator $url)
+    protected $extensions;
+
+    public function __construct(UrlGenerator $url, ExtensionManager $extensions)
    {
        $this->url = $url;
+        $this->extensions = $extensions;
    }

    public function __invoke(Configurator $config)
@@ -37,6 +47,10 @@ class ConfigureMentions
        $this->configureUserMentions($config);
        $this->configurePostMentions($config);
        $this->configureGroupMentions($config);
+
+        if ($this->extensions->isEnabled('flarum-tags')) {
+            $this->configureTagMentions($config);
+        }
    }

    private function configureUserMentions(Configurator $config): void
@@ -58,15 +72,19 @@ class ConfigureMentions
                    <span class="UserMention UserMention--deleted">@<xsl:value-of select="@displayname"/></span>
                </xsl:otherwise>
            </xsl:choose>';
+
        $tag->filterChain->prepend([static::class, 'addUserId'])
            ->setJS('function(tag) { return flarum.extensions["flarum-mentions"].filterUserMentions(tag); }');

-        $config->Preg->match('/\B@["|“](?<displayname>((?!"#[a-z]{0,3}[0-9]+).)+)["|”]#(?<id>[0-9]+)\b/', $tagName);
+        $tag->filterChain->append([static::class, 'dummyFilter'])
+            ->setJs('function(tag) { return flarum.extensions["flarum-mentions"].postFilterUserMentions(tag); }');
+
+        $config->Preg->match('/\B@["“](?<displayname>((?!"#[a-z]{0,3}[0-9]+).)+)["”]#(?<id>[0-9]+)\b/', $tagName);
        $config->Preg->match('/\B@(?<username>[a-z0-9_-]+)(?!#)/i', $tagName);
    }

    /**
-     * @param Tag $tag
+     * @param FormatterTag $tag
     * @return bool|void
     */
    public static function addUserId($tag)
@@ -117,11 +135,14 @@ class ConfigureMentions
            ->setJS('function(tag) { return flarum.extensions["flarum-mentions"].filterPostMentions(tag); }')
            ->addParameterByName('actor');

-        $config->Preg->match('/\B@["|“](?<displayname>((?!"#[a-z]{0,3}[0-9]+).)+)["|”]#p(?<id>[0-9]+)\b/', $tagName);
+        $tag->filterChain->append([static::class, 'dummyFilter'])
+            ->setJs('function(tag) { return flarum.extensions["flarum-mentions"].postFilterPostMentions(tag); }');
+
+        $config->Preg->match('/\B@["“](?<displayname>((?!"#[a-z]{0,3}[0-9]+).)+)["”]#p(?<id>[0-9]+)\b/', $tagName);
    }

    /**
-     * @param Tag $tag
+     * @param FormatterTag $tag
     * @return bool|void
     */
    public static function addPostId($tag, User $actor)
@@ -148,8 +169,6 @@ class ConfigureMentions

        $tag = $config->tags->add($tagName);
        $tag->attributes->add('groupname');
-        $tag->attributes->add('icon');
-        $tag->attributes->add('color');
        $tag->attributes->add('id')->filterChain->append('#uint');

        $tag->template = '
@@ -157,7 +176,7 @@ class ConfigureMentions
                <xsl:when test="@deleted != 1">
                    <xsl:choose>
                        <xsl:when test="string(@color) != \'\'">
-                            <span class="GroupMention GroupMention--colored" style="--group-color:{@color};">
+                            <span class="GroupMention GroupMention--colored" style="--color:{@color};">
                                <span class="GroupMention-name">@<xsl:value-of select="@groupname"/></span>
                                <xsl:if test="string(@icon) != \'\'">
                                    <i class="icon {@icon}"></i>
@@ -183,29 +202,130 @@ class ConfigureMentions
                    </span>
                </xsl:otherwise>
            </xsl:choose>';
-        $tag->filterChain->prepend([static::class, 'addGroupId'])
-            ->setJS('function(tag) { return flarum.extensions["flarum-mentions"].filterGroupMentions(tag); }');

-        $config->Preg->match('/\B@["|“](?<groupname>((?!"#[a-z]{0,3}[0-9]+).)+)["|”]#g(?<id>[0-9]+)\b/', $tagName);
+        $tag->filterChain->prepend([static::class, 'addGroupId'])
+            ->setJS('function(tag) { return flarum.extensions["flarum-mentions"].filterGroupMentions(tag); }')
+            ->addParameterByName('actor');
+
+        $tag->filterChain->append([static::class, 'dummyFilter'])
+            ->setJS('function(tag) { return flarum.extensions["flarum-mentions"].postFilterGroupMentions(tag); }');
+
+        $config->Preg->match('/\B@["“](?<groupname>((?!"#[a-z]{0,3}[0-9]+).)+)["|”]#g(?<id>[0-9]+)\b/', $tagName);
    }

    /**
-     * @param $tag
     * @return bool|void
     */
-    public static function addGroupId($tag)
+    public static function addGroupId(FormatterTag $tag, User $actor)
    {
-        $group = Group::find($tag->getAttribute('id'));
+        $id = $tag->getAttribute('id');

-        if (isset($group) && ! in_array($group->id, [Group::GUEST_ID, Group::MEMBER_ID])) {
+        if ($actor->cannot('mentionGroups') || in_array($id, [Group::GUEST_ID, Group::MEMBER_ID])) {
+            $tag->invalidate();
+
+            return false;
+        }
+
+        $group = resolve(GroupRepository::class)
+            ->queryVisibleTo($actor)
+            ->find($id);
+
+        if ($group) {
            $tag->setAttribute('id', $group->id);
            $tag->setAttribute('groupname', $group->name_plural);
-            $tag->setAttribute('icon', $group->icon ?? 'fas fa-at');
-            $tag->setAttribute('color', $group->color);

            return true;
        }

        $tag->invalidate();
    }
+
+    private function configureTagMentions(Configurator $config)
+    {
+        $config->rendering->parameters['TAG_URL'] = $this->url->to('forum')->route('tag', ['slug' => '']);
+
+        $tagName = 'TAGMENTION';
+
+        $tag = $config->tags->add($tagName);
+        $tag->attributes->add('tagname');
+        $tag->attributes->add('slug');
+        $tag->attributes->add('id')->filterChain->append('#uint');
+
+        $tag->template = '
+            <xsl:choose>
+                <xsl:when test="@deleted != 1">
+                    <a href="{$TAG_URL}{@slug}" data-id="{@id}">
+                        <xsl:attribute name="class">
+                            <xsl:choose>
+                                <xsl:when test="@color != \'\'">
+                                    <xsl:text>TagMention TagMention--colored</xsl:text>
+                                </xsl:when>
+                                <xsl:otherwise>
+                                    <xsl:text>TagMention</xsl:text>
+                                </xsl:otherwise>
+                            </xsl:choose>
+                        </xsl:attribute>
+                        <xsl:attribute name="style">
+                            <xsl:choose>
+                                <xsl:when test="@color != \'\'">
+                                    <xsl:text>--color:</xsl:text>
+                                    <xsl:value-of select="@color"/>
+                                </xsl:when>
+                            </xsl:choose>
+                        </xsl:attribute>
+                        <span class="TagMention-text">
+                            <xsl:if test="@icon != \'\'">
+                                <i class="icon {@icon}"></i>
+                            </xsl:if>
+                            <xsl:value-of select="@tagname"/>
+                        </span>
+                    </a>
+                </xsl:when>
+                <xsl:otherwise>
+                    <span class="TagMention TagMention--deleted" data-id="{@id}">
+                        <span class="TagMention-text">
+                            <xsl:value-of select="@tagname"/>
+                        </span>
+                    </span>
+                </xsl:otherwise>
+            </xsl:choose>';
+
+        $tag->filterChain
+            ->prepend([static::class, 'addTagId'])
+            ->setJS('function(tag) { return flarum.extensions["flarum-mentions"].filterTagMentions(tag); }')
+            ->addParameterByName('actor');
+
+        $tag->filterChain
+            ->append([static::class, 'dummyFilter'])
+            ->setJS('function(tag) { return flarum.extensions["flarum-mentions"].postFilterTagMentions(tag); }');
+
+        $config->Preg->match('/(?:[^“"]|^)\B#(?<slug>[-_\p{L}\p{N}\p{M}]+)\b/ui', $tagName);
+    }
+
+    /**
+     * @return true|void
+     */
+    public static function addTagId(FormatterTag $tag, User $actor)
+    {
+        /** @var Tag|null $model */
+        $model = resolve(TagRepository::class)
+            ->queryVisibleTo($actor)
+            ->firstWhere('slug', $tag->getAttribute('slug'));
+
+        if ($model) {
+            $tag->setAttribute('id', (string) $model->id);
+            $tag->setAttribute('tagname', $model->name);
+
+            return true;
+        }
+    }
+
+    /**
+     * Used when only an append JS filter is needed,
+     * to add post tag validation attributes.
+     */
+    public static function dummyFilter(): bool
+    {
+        return true;
+    }
 }
--- a/extensions/mentions/src/FilterVisiblePosts.php
+++ b/extensions/mentions/src/FilterVisiblePosts.php
--- a/extensions/mentions/src/Formatter/CheckPermissions.php
+++ b/extensions/mentions/src/Formatter/CheckPermissions.php
@@ -1,26 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Mentions\Formatter;
-
-use Flarum\User\User;
-use s9e\TextFormatter\Parser;
-
-class CheckPermissions
-{
-    public function __invoke(Parser $parser, $content, string $text, ?User $actor): string
-    {
-        // Check user has `mentionGroups` permission, if not, remove the `GROUPMENTION` tag from the parser.
-        if ($actor && $actor->cannot('mentionGroups')) {
-            $parser->disableTag('GROUPMENTION');
-        }
-
-        return $text;
-    }
-}
--- a/extensions/mentions/src/Formatter/FormatGroupMentions.php
+++ b/extensions/mentions/src/Formatter/FormatGroupMentions.php
@@ -39,8 +39,8 @@ class FormatGroupMentions
    {
        return Utils::replaceAttributes($xml, 'GROUPMENTION', function ($attributes) use ($context) {
            $group = (($context && isset($context->getRelations()['mentionsGroups'])) || $context instanceof Post)
-            ? $context->mentionsGroups->find($attributes['id'])
-            : Group::find($attributes['id']);
+                ? $context->mentionsGroups->find($attributes['id'])
+                : Group::find($attributes['id']);

            if ($group) {
                $attributes['groupname'] = $group->name_plural;
--- a/extensions/mentions/src/Formatter/FormatTagMentions.php
+++ b/extensions/mentions/src/Formatter/FormatTagMentions.php
@@ -0,0 +1,41 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Mentions\Formatter;
+
+use Flarum\Post\Post;
+use Flarum\Tags\Tag;
+use Psr\Http\Message\ServerRequestInterface as Request;
+use s9e\TextFormatter\Renderer;
+use s9e\TextFormatter\Utils;
+
+class FormatTagMentions
+{
+    public function __invoke(Renderer $renderer, $context, ?string $xml, Request $request = null): string
+    {
+        return Utils::replaceAttributes($xml, 'TAGMENTION', function ($attributes) use ($context) {
+            /** @var Tag|null $tag */
+            $tag = (($context && isset($context->getRelations()['mentionsTags'])) || $context instanceof Post)
+                ? $context->mentionsTags->find($attributes['id'])
+                : Tag::query()->find($attributes['id']);
+
+            if ($tag) {
+                $attributes['deleted'] = false;
+                $attributes['tagname'] = $tag->name;
+                $attributes['slug'] = $tag->slug;
+                $attributes['color'] = $tag->color ?? '';
+                $attributes['icon'] = $tag->icon ?? '';
+            } else {
+                $attributes['deleted'] = true;
+            }
+
+            return $attributes;
+        });
+    }
+}
--- a/extensions/mentions/src/Formatter/UnparseTagMentions.php
+++ b/extensions/mentions/src/Formatter/UnparseTagMentions.php
@@ -0,0 +1,77 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Mentions\Formatter;
+
+use Flarum\Post\Post;
+use Flarum\Tags\Tag;
+use s9e\TextFormatter\Utils;
+
+class UnparseTagMentions
+{
+    /**
+     * Configure rendering for user mentions.
+     *
+     * @param string $xml
+     * @param mixed $context
+     * @return string $xml to be unparsed
+     */
+    public function __invoke($context, string $xml)
+    {
+        $xml = $this->updateTagMentionTags($context, $xml);
+        $xml = $this->unparseTagMentionTags($xml);
+
+        return $xml;
+    }
+
+    /**
+     * Updates XML user mention tags before unparsing so that unparsing uses new tag names.
+     *
+     * @param mixed $context
+     * @param string $xml : Parsed text.
+     * @return string $xml : Updated XML tags;
+     */
+    protected function updateTagMentionTags($context, string $xml): string
+    {
+        return Utils::replaceAttributes($xml, 'TAGMENTION', function (array $attributes) use ($context) {
+            /** @var Tag|null $tag */
+            $tag = (($context && isset($context->getRelations()['mentionsTags'])) || $context instanceof Post)
+                ? $context->mentionsTags->find($attributes['id'])
+                : Tag::query()->find($attributes['id']);
+
+            if ($tag) {
+                $attributes['tagname'] = $tag->name;
+                $attributes['slug'] = $tag->slug;
+            }
+
+            return $attributes;
+        });
+    }
+
+    /**
+     * Transforms tag mention tags from XML to raw unparsed content with updated name.
+     *
+     * @param string $xml : Parsed text.
+     * @return string : Unparsed text.
+     */
+    protected function unparseTagMentionTags(string $xml): string
+    {
+        $tagName = 'TAGMENTION';
+
+        if (strpos($xml, $tagName) === false) {
+            return $xml;
+        }
+
+        return preg_replace(
+            '/<'.preg_quote($tagName).'\b[^>]*(?=\bid="([0-9]+)")[^>]*(?=\bslug="(.*)")[^>]*>@[^<]+<\/'.preg_quote($tagName).'>/U',
+            '#$2',
+            $xml
+        );
+    }
+}
--- a/extensions/mentions/src/Listener/UpdateMentionsMetadataWhenInvisible.php
+++ b/extensions/mentions/src/Listener/UpdateMentionsMetadataWhenInvisible.php
@@ -9,6 +9,7 @@

 namespace Flarum\Mentions\Listener;

+use Flarum\Extension\ExtensionManager;
 use Flarum\Mentions\Notification\UserMentionedBlueprint;
 use Flarum\Notification\NotificationSyncer;
 use Flarum\Post\Event\Deleted;
@@ -22,11 +23,14 @@ class UpdateMentionsMetadataWhenInvisible
    protected $notifications;

    /**
-     * @param NotificationSyncer $notifications
+     * @var ExtensionManager
     */
-    public function __construct(NotificationSyncer $notifications)
+    protected $extensions;
+
+    public function __construct(NotificationSyncer $notifications, ExtensionManager $extensions)
    {
        $this->notifications = $notifications;
+        $this->extensions = $extensions;
    }

    /**
@@ -43,5 +47,10 @@ class UpdateMentionsMetadataWhenInvisible

        // Remove group mentions
        $event->post->mentionsGroups()->sync([]);
+
+        // Remove tag mentions
+        if ($this->extensions->isEnabled('flarum-tags')) {
+            $event->post->mentionsTags()->sync([]);
+        }
    }
 }
--- a/extensions/mentions/src/Listener/UpdateMentionsMetadataWhenVisible.php
+++ b/extensions/mentions/src/Listener/UpdateMentionsMetadataWhenVisible.php
@@ -10,6 +10,7 @@
 namespace Flarum\Mentions\Listener;

 use Flarum\Approval\Event\PostWasApproved;
+use Flarum\Extension\ExtensionManager;
 use Flarum\Mentions\Notification\GroupMentionedBlueprint;
 use Flarum\Mentions\Notification\PostMentionedBlueprint;
 use Flarum\Mentions\Notification\UserMentionedBlueprint;
@@ -30,11 +31,14 @@ class UpdateMentionsMetadataWhenVisible
    protected $notifications;

    /**
-     * @param NotificationSyncer $notifications
+     * @var ExtensionManager
     */
-    public function __construct(NotificationSyncer $notifications)
+    protected $extensions;
+
+    public function __construct(NotificationSyncer $notifications, ExtensionManager $extensions)
    {
        $this->notifications = $notifications;
+        $this->extensions = $extensions;
    }

    /**
@@ -62,6 +66,13 @@ class UpdateMentionsMetadataWhenVisible
            $event->post,
            Utils::getAttributeValues($content, 'GROUPMENTION', 'id')
        );
+
+        if ($this->extensions->isEnabled('flarum-tags')) {
+            $this->syncTagMentions(
+                $event->post,
+                Utils::getAttributeValues($content, 'TAGMENTION', 'id')
+            );
+        }
    }

    protected function syncUserMentions(Post $post, array $mentioned)
@@ -113,4 +124,10 @@ class UpdateMentionsMetadataWhenVisible

        $this->notifications->sync(new GroupMentionedBlueprint($post), $users);
    }
+
+    protected function syncTagMentions(Post $post, array $mentioned)
+    {
+        $post->mentionsTags()->sync($mentioned);
+        $post->unsetRelation('mentionsTags');
+    }
 }
--- a/extensions/mentions/tests/integration/api/GroupMentionsTest.php
+++ b/extensions/mentions/tests/integration/api/GroupMentionsTest.php
@@ -33,40 +33,30 @@ class GroupMentionsTest extends TestCase
            'users' => [
                ['id' => 3, 'username' => 'potato', 'email' => 'potato@machine.local', 'is_email_confirmed' => 1],
                ['id' => 4, 'username' => 'toby', 'email' => 'toby@machine.local', 'is_email_confirmed' => 1],
-                ['id' => 5, 'username' => 'bad_user', 'email' => 'bad_user@machine.local', 'is_email_confirmed' => 1],
            ],
            'discussions' => [
                ['id' => 2, 'title' => __CLASS__, 'created_at' => Carbon::now(), 'last_posted_at' => Carbon::now(), 'user_id' => 3, 'first_post_id' => 4, 'comment_count' => 2],
            ],
            'posts' => [
-                ['id' => 4, 'number' => 2, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 3, 'type' => 'comment', 'content' => '<r><p>One of the <GROUPMENTION color="#80349E" groupname="Mods" icon="fas fa-bolt" id="4">@"Mods"#g4</GROUPMENTION> will look at this</p></r>'],
-                ['id' => 6, 'number' => 3, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 3, 'type' => 'comment', 'content' => '<r><p><GROUPMENTION color="#80349E" groupname="OldGroupName" icon="fas fa-circle" id="100">@"OldGroupName"#g100</GROUPMENTION></p></r>'],
-                ['id' => 7, 'number' => 4, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 3, 'type' => 'comment', 'content' => '<r><p><GROUPMENTION color="#000" groupname="OldGroupName" icon="fas fa-circle" id="11">@"OldGroupName"#g11</GROUPMENTION></p></r>'],
+                ['id' => 4, 'number' => 2, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 3, 'type' => 'comment', 'content' => '<r><p>One of the <GROUPMENTION groupname="Mods" id="4">@"Mods"#g4</GROUPMENTION> will look at this</p></r>'],
+                ['id' => 6, 'number' => 3, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 3, 'type' => 'comment', 'content' => '<r><p><GROUPMENTION groupname="OldGroupName" id="100">@"OldGroupName"#g100</GROUPMENTION></p></r>'],
+                ['id' => 7, 'number' => 4, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 3, 'type' => 'comment', 'content' => '<r><p><GROUPMENTION groupname="OldGroupName" id="11">@"OldGroupName"#g11</GROUPMENTION></p></r>'],
            ],
            'post_mentions_group' => [
                ['post_id' => 4, 'mentions_group_id' => 4],
                ['post_id' => 7, 'mentions_group_id' => 11],
            ],
+            'group_user' => [
+                ['group_id' => 9, 'user_id' => 4],
+            ],
            'group_permission' => [
                ['group_id' => Group::MEMBER_ID, 'permission' => 'postWithoutThrottle'],
+                ['group_id' => 9, 'permission' => 'mentionGroups'],
            ],
            'groups' => [
-                [
-                    'id' => 10,
-                    'name_singular' => 'Hidden',
-                    'name_plural' => 'Ninjas',
-                    'color' => null,
-                    'icon' => 'fas fa-wrench',
-                    'is_hidden' => 1
-                ],
-                [
-                    'id' => 11,
-                    'name_singular' => 'Fresh Name',
-                    'name_plural' => 'Fresh Name',
-                    'color' => '#ccc',
-                    'icon' => 'fas fa-users',
-                    'is_hidden' => 0
-                ]
+                ['id' => 9, 'name_singular' => 'HasPermissionToMentionGroups', 'name_plural' => 'test'],
+                ['id' => 10, 'name_singular' => 'Hidden', 'name_plural' => 'Ninjas', 'icon' => 'fas fa-wrench', 'color' => '#000', 'is_hidden' => 1],
+                ['id' => 11, 'name_singular' => 'Fresh Name', 'name_plural' => 'Fresh Name', 'color' => '#ccc', 'icon' => 'fas fa-users', 'is_hidden' => 0]
            ]
        ]);
    }
@@ -324,15 +314,9 @@ class GroupMentionsTest extends TestCase
     */
    public function user_with_permission_can_mention_groups()
    {
-        $this->prepareDatabase([
-            'group_permission' => [
-                ['group_id' => Group::MEMBER_ID, 'permission' => 'mentionGroups'],
-            ]
-        ]);
-
        $response = $this->send(
            $this->request('POST', '/api/posts', [
-                'authenticatedAs' => 3,
+                'authenticatedAs' => 4,
                'json' => [
                    'data' => [
                        'attributes' => [
@@ -361,15 +345,9 @@ class GroupMentionsTest extends TestCase
     */
    public function user_with_permission_cannot_mention_hidden_groups()
    {
-        $this->prepareDatabase([
-            'group_permission' => [
-                ['group_id' => Group::MEMBER_ID, 'permission' => 'mentionGroups'],
-            ]
-        ]);
-
        $response = $this->send(
            $this->request('POST', '/api/posts', [
-                'authenticatedAs' => 3,
+                'authenticatedAs' => 4,
                'json' => [
                    'data' => [
                        'attributes' => [
--- a/extensions/mentions/tests/integration/api/TagMentionsTest.php
+++ b/extensions/mentions/tests/integration/api/TagMentionsTest.php
@@ -0,0 +1,385 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Mentions\Tests\integration\api;
+
+use Carbon\Carbon;
+use Flarum\Group\Group;
+use Flarum\Post\CommentPost;
+use Flarum\Testing\integration\RetrievesAuthorizedUsers;
+use Flarum\Testing\integration\TestCase;
+
+class TagMentionsTest extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->extension('flarum-tags', 'flarum-mentions');
+
+        $this->prepareDatabase([
+            'users' => [
+                ['id' => 3, 'username' => 'potato', 'email' => 'potato@machine.local', 'is_email_confirmed' => 1],
+                ['id' => 4, 'username' => 'toby', 'email' => 'toby@machine.local', 'is_email_confirmed' => 1],
+            ],
+            'discussions' => [
+                ['id' => 2, 'title' => __CLASS__, 'created_at' => Carbon::now(), 'last_posted_at' => Carbon::now(), 'user_id' => 3, 'first_post_id' => 4, 'comment_count' => 2],
+            ],
+            'posts' => [
+                ['id' => 4, 'number' => 2, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 3, 'type' => 'comment', 'content' => '<r><TAGMENTION id="1" slug="test_old_slug" tagname="TestOldName">#test_old_slug</TAGMENTION></r>'],
+                ['id' => 7, 'number' => 5, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 2021, 'type' => 'comment', 'content' => '<r><TAGMENTION id="3" slug="support" tagname="Support">#deleted_relation</TAGMENTION></r>'],
+                ['id' => 8, 'number' => 6, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 4, 'type' => 'comment', 'content' => '<r><TAGMENTION id="2020" slug="i_am_a_deleted_tag" tagname="i_am_a_deleted_tag">#i_am_a_deleted_tag</TAGMENTION></r>'],
+                ['id' => 10, 'number' => 11, 'discussion_id' => 2, 'created_at' => Carbon::now(), 'user_id' => 4, 'type' => 'comment', 'content' => '<r><TAGMENTION id="5" slug="laravel">#laravel</TAGMENTION></r>'],
+            ],
+            'tags' => [
+                ['id' => 1, 'name' => 'Test', 'slug' => 'test', 'is_restricted' => 0],
+                ['id' => 2, 'name' => 'Flarum', 'slug' => 'flarum', 'is_restricted' => 0],
+                ['id' => 3, 'name' => 'Support', 'slug' => 'support', 'is_restricted' => 0],
+                ['id' => 4, 'name' => 'Dev', 'slug' => 'dev', 'is_restricted' => 1],
+                ['id' => 5, 'name' => 'Laravel "#t6 Tag', 'slug' => 'laravel', 'is_restricted' => 0],
+                ['id' => 6, 'name' => 'Tatakai', 'slug' => '戦い', 'is_restricted' => 0],
+            ],
+            'post_mentions_tag' => [
+                ['post_id' => 4, 'mentions_tag_id' => 1],
+                ['post_id' => 5, 'mentions_tag_id' => 2],
+                ['post_id' => 6, 'mentions_tag_id' => 3],
+                ['post_id' => 10, 'mentions_tag_id' => 4],
+                ['post_id' => 10, 'mentions_tag_id' => 5],
+            ],
+            'group_permission' => [
+                ['group_id' => Group::MEMBER_ID, 'permission' => 'postWithoutThrottle'],
+            ],
+        ]);
+    }
+
+    /** @test */
+    public function mentioning_a_valid_tag_with_valid_format_works()
+    {
+        $response = $this->send(
+            $this->request('POST', '/api/posts', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#flarum',
+                        ],
+                        'relationships' => [
+                            'discussion' => ['data' => ['id' => 2]],
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertStringNotContainsString('TagMention--deleted', $response['data']['attributes']['contentHtml']);
+        $this->assertNotNull(CommentPost::find($response['data']['id'])->mentionsTags->find(2));
+    }
+
+    /** @test */
+    public function mentioning_a_valid_tag_using_cjk_slug_with_valid_format_works()
+    {
+        $response = $this->send(
+            $this->request('POST', '/api/posts', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#戦い',
+                        ],
+                        'relationships' => [
+                            'discussion' => ['data' => ['id' => 2]],
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString('Tatakai', $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertStringNotContainsString('TagMention--deleted', $response['data']['attributes']['contentHtml']);
+        $this->assertNotNull(CommentPost::find($response['data']['id'])->mentionsTags->find(6));
+    }
+
+    /** @test */
+    public function mentioning_an_invalid_tag_doesnt_work()
+    {
+        $response = $this->send(
+            $this->request('POST', '/api/posts', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#franzofflarum',
+                        ],
+                        'relationships' => [
+                            'discussion' => ['data' => ['id' => 2]],
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertEquals('#franzofflarum', $response['data']['attributes']['content']);
+        $this->assertStringNotContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertCount(0, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function mentioning_a_tag_when_tags_disabled_does_not_cause_errors()
+    {
+        $this->extensions = ['flarum-mentions'];
+
+        $response = $this->send(
+            $this->request('POST', '/api/posts', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#test',
+                        ],
+                        'relationships' => [
+                            'discussion' => ['data' => ['id' => 2]],
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertEquals('#test', $response['data']['attributes']['content']);
+        $this->assertStringNotContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertNull(CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function mentioning_a_restricted_tag_doesnt_work_without_privileges()
+    {
+        $response = $this->send(
+            $this->request('POST', '/api/posts', [
+                'authenticatedAs' => 3,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#dev',
+                        ],
+                        'relationships' => [
+                            'discussion' => ['data' => ['id' => 2]],
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertEquals('#dev', $response['data']['attributes']['content']);
+        $this->assertStringNotContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertCount(0, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function mentioning_a_restricted_tag_works_with_privileges()
+    {
+        $response = $this->send(
+            $this->request('POST', '/api/posts', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#dev',
+                        ],
+                        'relationships' => [
+                            'discussion' => ['data' => ['id' => 2]],
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertEquals('#dev', $response['data']['attributes']['content']);
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertCount(1, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function mentioning_multiple_tags_works()
+    {
+        $response = $this->send(
+            $this->request('POST', '/api/posts', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#test #flarum #support #laravel #franzofflarum',
+                        ],
+                        'relationships' => [
+                            'discussion' => ['data' => ['id' => 2]],
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(201, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString('Test', $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString('Flarum', $response['data']['attributes']['contentHtml']);
+        $this->assertEquals('#test #flarum #support #laravel #franzofflarum', $response['data']['attributes']['content']);
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertStringNotContainsString('TagMention--deleted', $response['data']['attributes']['contentHtml']);
+        $this->assertCount(4, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function tag_mentions_render_with_fresh_data()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/posts/4', [
+                'authenticatedAs' => 1,
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString('Test', $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertCount(1, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function tag_mentions_dont_cause_errors_when_tags_disabled()
+    {
+        $this->extensions = ['flarum-mentions'];
+
+        $response = $this->send(
+            $this->request('GET', '/api/posts/4', [
+                'authenticatedAs' => 1,
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+    }
+
+    /** @test */
+    public function tag_mentions_unparse_with_fresh_data()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/posts/4', [
+                'authenticatedAs' => 1,
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString('#test', $response['data']['attributes']['content']);
+        $this->assertCount(1, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function deleted_tag_mentions_unparse_and_render_as_expected()
+    {
+        // No reason to hide a deleted tag's name.
+        $deleted_text = 'i_am_a_deleted_tag';
+
+        $response = $this->send(
+            $this->request('GET', '/api/posts/8', [
+                'authenticatedAs' => 1,
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString($deleted_text, $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString("#$deleted_text", $response['data']['attributes']['content']);
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString('TagMention--deleted', $response['data']['attributes']['contentHtml']);
+        $this->assertCount(0, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function deleted_tag_mentions_relation_unparse_and_render_as_expected()
+    {
+        // No reason to hide a deleted tag's name.
+        $deleted_text = 'deleted_relation';
+
+        $response = $this->send(
+            $this->request('GET', '/api/posts/7', [
+                'authenticatedAs' => 1,
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString('Support', $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString("#$deleted_text", $response['data']['attributes']['content']);
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertStringContainsString('TagMention--deleted', $response['data']['attributes']['contentHtml']);
+        $this->assertCount(0, CommentPost::find($response['data']['id'])->mentionsTags);
+    }
+
+    /** @test */
+    public function editing_a_post_that_has_a_tag_mention_works()
+    {
+        $response = $this->send(
+            $this->request('PATCH', '/api/posts/10', [
+                'authenticatedAs' => 1,
+                'json' => [
+                    'data' => [
+                        'attributes' => [
+                            'content' => '#laravel',
+                        ],
+                    ],
+                ],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+
+        $response = json_decode($response->getBody(), true);
+
+        $this->assertStringContainsString('Laravel "#t6 Tag', $response['data']['attributes']['contentHtml']);
+        $this->assertEquals('#laravel', $response['data']['attributes']['content']);
+        $this->assertStringContainsString('TagMention', $response['data']['attributes']['contentHtml']);
+        $this->assertNotNull(CommentPost::find($response['data']['id'])->mentionsTags->find(5));
+    }
+}
--- a/extensions/tags/extend.php
+++ b/extensions/tags/extend.php
@@ -29,6 +29,8 @@ use Flarum\Tags\Listener;
 use Flarum\Tags\LoadForumTagsRelationship;
 use Flarum\Tags\Post\DiscussionTaggedPost;
 use Flarum\Tags\Query\TagFilterGambit;
+use Flarum\Tags\Search\Gambit\FulltextGambit;
+use Flarum\Tags\Search\TagSearcher;
 use Flarum\Tags\Tag;
 use Flarum\Tags\Utf8SlugDriver;
 use Psr\Http\Message\ServerRequestInterface;
@@ -135,6 +137,9 @@ return [
    (new Extend\SimpleFlarumSearch(DiscussionSearcher::class))
        ->addGambit(TagFilterGambit::class),

+    (new Extend\SimpleFlarumSearch(TagSearcher::class))
+        ->setFullTextGambit(FullTextGambit::class),
+
    (new Extend\ModelUrl(Tag::class))
        ->addSlugDriver('default', Utf8SlugDriver::class),
 ];
--- a/extensions/tags/less/common/TagLabel.less
+++ b/extensions/tags/less/common/TagLabel.less
@@ -1,35 +1,39 @@
-.TagLabel {
-  font-size: 85%;
+.tag-label() {
  font-weight: 600;
-  display: inline-block;
-  padding: 0.1em 0.5em;
-  border-radius: @border-radius;
+  border-radius: var(--border-radius);
  background: var(--tag-bg);
  color: var(--tag-color);
  text-transform: none;
  text-decoration: none !important;
-  vertical-align: bottom;

  &.untagged {
    --tag-bg: transparent;
-    --tag-color: @muted-color;
+    --tag-color: var(--muted-color);
    border: 1px dotted;
  }

-  &.colored {
+  &.colored, &--colored {
    --tag-color: var(--contrast-color, var(--body-bg));
-
-    .TagLabel-text {
-      color: var(--tag-color) !important;
-    }
  }

+  &.colored &-text, &--colored &-text {
+    color: var(--tag-color) !important;
+  }
+}
+
+.TagLabel {
+  .tag-label();
+  font-size: 85%;
+  display: inline-block;
+  padding: 0.1em 0.5em;
+  vertical-align: bottom;
+
  .DiscussionHero .TagsLabel & {
    background: transparent;
    border-radius: @border-radius !important;
    font-size: 14px;

-    &.colored {
+    &.colored, &--colored {
      --tag-color: var(--tag-bg);
      margin-right: 5px;
      background-color: var(--contrast-color, var(--body-bg));
--- a/extensions/tags/migrations/2023_03_01_000000_create_post_mentions_tag_table.php
+++ b/extensions/tags/migrations/2023_03_01_000000_create_post_mentions_tag_table.php
@@ -0,0 +1,49 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+use Flarum\Database\Migration;
+use Illuminate\Database\Schema\Blueprint;
+
+/**
+ * Why does this migration reside here rather than in the mentions extension?
+ *
+ * To be able to use a foreign key constraint on the `mentions_tag_id` column,
+ * we need to create the `post_mentions_tag` table after the `tags` table has
+ * been created. This is not possible in the mentions extension, because the
+ * tags extension is not always enabled.
+ *
+ * Other solutions such as conditional migrations have more implications and
+ * require more changes to the process of enabling/disabling extensions.
+ * @link https://github.com/flarum/framework/pull/3689
+ *
+ * This is a temporary solution until we implement mentionable models in v2.0.
+ * @link https://github.com/orgs/flarum/projects/22/views/1?pane=issue&itemId=21752599
+ *
+ * At the same time, because of https://github.com/flarum/issue-archive/issues/44,
+ * we need a way to track which tags are referenced in a tag change event post,
+ * so this might actually be a permanent solution.
+ */
+return Migration::createTable(
+    'post_mentions_tag',
+    function (Blueprint $table) {
+        $table->unsignedInteger('post_id');
+        $table->foreign('post_id')
+            ->references('id')
+            ->on('posts')
+            ->cascadeOnDelete();
+        $table->unsignedInteger('mentions_tag_id');
+        $table->foreign('mentions_tag_id')
+            ->references('id')
+            ->on('tags')
+            ->cascadeOnDelete();
+        $table->dateTime('created_at')->useCurrent()->nullable();
+
+        $table->primary(['post_id', 'mentions_tag_id']);
+    }
+);
--- a/extensions/tags/src/Api/Controller/ListTagsController.php
+++ b/extensions/tags/src/Api/Controller/ListTagsController.php
@@ -11,7 +11,10 @@ namespace Flarum\Tags\Api\Controller;

 use Flarum\Api\Controller\AbstractListController;
 use Flarum\Http\RequestUtil;
+use Flarum\Http\UrlGenerator;
+use Flarum\Query\QueryCriteria;
 use Flarum\Tags\Api\Serializer\TagSerializer;
+use Flarum\Tags\Search\TagSearcher;
 use Flarum\Tags\TagRepository;
 use Psr\Http\Message\ServerRequestInterface;
 use Tobscure\JsonApi\Document;
@@ -44,9 +47,21 @@ class ListTagsController extends AbstractListController
     */
    protected $tags;

-    public function __construct(TagRepository $tags)
+    /**
+     * @var TagSearcher
+     */
+    protected $searcher;
+
+    /**
+     * @var UrlGenerator
+     */
+    protected $url;
+
+    public function __construct(TagRepository $tags, TagSearcher $searcher, UrlGenerator $url)
    {
        $this->tags = $tags;
+        $this->searcher = $searcher;
+        $this->url = $url;
    }

    /**
@@ -56,15 +71,33 @@ class ListTagsController extends AbstractListController
    {
        $actor = RequestUtil::getActor($request);
        $include = $this->extractInclude($request);
+        $filters = $this->extractFilter($request);
+        $limit = $this->extractLimit($request);
+        $offset = $this->extractOffset($request);

        if (in_array('lastPostedDiscussion', $include)) {
            $include = array_merge($include, ['lastPostedDiscussion.tags', 'lastPostedDiscussion.state']);
        }

-        return $this->tags
-            ->with($include, $actor)
-            ->whereVisibleTo($actor)
-            ->withStateFor($actor)
-            ->get();
+        if (array_key_exists('q', $filters)) {
+            $results = $this->searcher->search(new QueryCriteria($actor, $filters), $limit, $offset);
+            $tags = $results->getResults();
+
+            $document->addPaginationLinks(
+                $this->url->to('api')->route('tags.index'),
+                $request->getQueryParams(),
+                $offset,
+                $limit,
+                $results->areMoreResults() ? null : 0
+            );
+        } else {
+            $tags = $this->tags
+                ->with($include, $actor)
+                ->whereVisibleTo($actor)
+                ->withStateFor($actor)
+                ->get();
+        }
+
+        return $tags;
    }
 }
--- a/extensions/tags/src/Search/Gambit/FulltextGambit.php
+++ b/extensions/tags/src/Search/Gambit/FulltextGambit.php
@@ -0,0 +1,48 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tags\Search\Gambit;
+
+use Flarum\Search\GambitInterface;
+use Flarum\Search\SearchState;
+use Flarum\Tags\TagRepository;
+use Illuminate\Database\Eloquent\Builder;
+
+class FulltextGambit implements GambitInterface
+{
+    /**
+     * @var TagRepository
+     */
+    protected $tags;
+
+    public function __construct(TagRepository $tags)
+    {
+        $this->tags = $tags;
+    }
+
+    private function getTagSearchSubQuery(string $searchValue): Builder
+    {
+        return $this->tags
+            ->query()
+            ->select('id')
+            ->where('name', 'like', "$searchValue%")
+            ->orWhere('slug', 'like', "$searchValue%");
+    }
+
+    public function apply(SearchState $search, $searchValue)
+    {
+        $search->getQuery()
+            ->whereIn(
+                'id',
+                $this->getTagSearchSubQuery($searchValue)
+            );
+
+        return true;
+    }
+}
--- a/extensions/tags/src/Search/TagSearcher.php
+++ b/extensions/tags/src/Search/TagSearcher.php
@@ -0,0 +1,36 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tags\Search;
+
+use Flarum\Search\AbstractSearcher;
+use Flarum\Search\GambitManager;
+use Flarum\Tags\TagRepository;
+use Flarum\User\User;
+use Illuminate\Database\Eloquent\Builder;
+
+class TagSearcher extends AbstractSearcher
+{
+    /**
+     * @var TagRepository
+     */
+    protected $tags;
+
+    public function __construct(TagRepository $tags, GambitManager $gambits, array $searchMutators)
+    {
+        parent::__construct($gambits, $searchMutators);
+
+        $this->tags = $tags;
+    }
+
+    protected function getQuery(User $actor): Builder
+    {
+        return $this->tags->query()->whereVisibleTo($actor);
+    }
+}
--- a/extensions/tags/src/TagRepository.php
+++ b/extensions/tags/src/TagRepository.php
@@ -26,6 +26,11 @@ class TagRepository
        return Tag::query();
    }

+    public function queryVisibleTo(User $actor): Builder
+    {
+        return $this->scopeVisibleTo($this->query(), $actor);
+    }
+
    /**
     * @param array|string $relations
     * @param User $actor
--- a/extensions/tags/tests/integration/api/tags/ListWithFulltextSearchTest.php
+++ b/extensions/tags/tests/integration/api/tags/ListWithFulltextSearchTest.php
@@ -0,0 +1,81 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tags\Tests\integration\api\tags;
+
+use Flarum\Testing\integration\TestCase;
+use Illuminate\Support\Arr;
+
+class ListWithFulltextSearchTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->extension('flarum-tags');
+
+        $this->prepareDatabase([
+            'tags' => [
+                ['id' => 2, 'name' => 'Acme', 'slug' => 'acme'],
+                ['id' => 3, 'name' => 'Test', 'slug' => 'test'],
+                ['id' => 4, 'name' => 'Tag', 'slug' => 'tag'],
+                ['id' => 5, 'name' => 'Franz', 'slug' => 'franz'],
+                ['id' => 6, 'name' => 'Software', 'slug' => 'software'],
+                ['id' => 7, 'name' => 'Laravel', 'slug' => 'laravel'],
+                ['id' => 8, 'name' => 'Flarum', 'slug' => 'flarum'],
+                ['id' => 9, 'name' => 'Tea', 'slug' => 'tea'],
+                ['id' => 10, 'name' => 'Access', 'slug' => 'access'],
+            ],
+        ]);
+    }
+
+    /**
+     * @dataProvider searchDataProvider
+     * @test
+     */
+    public function can_search_for_tags(string $search, array $expected)
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/tags')->withQueryParams([
+                'filter' => [
+                    'q' => $search,
+                ],
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $this->assertEquals($expected, Arr::pluck($data, 'id'));
+    }
+
+    public function searchDataProvider(): array
+    {
+        return [
+            ['fla', [8]],
+            ['flarum', [8]],
+            ['flarums', []],
+            ['a', [2, 10]],
+            ['ac', [2, 10]],
+            ['ace', []],
+            ['acm', [2]],
+            ['acmes', []],
+            ['t', [3, 4, 9]],
+            ['te', [3, 9]],
+            ['test', [3]],
+            ['tag', [4]],
+            ['franz', [5]],
+            ['software', [6]],
+            ['lar', [7]],
+            ['laravel', [7]],
+            ['tea', [9]],
+            ['access', [10]],
+        ];
+    }
+}
--- a/framework/core/js/dist-typings/common/extenders/IExtender.d.ts
+++ b/framework/core/js/dist-typings/common/extenders/IExtender.d.ts
@@ -3,6 +3,6 @@ export interface IExtensionModule {
    name: string;
    exports: unknown;
 }
-export default interface IExtender {
-    extend(app: Application, extension: IExtensionModule): void;
+export default interface IExtender<App = Application> {
+    extend(app: App, extension: IExtensionModule): void;
 }
--- a/framework/core/js/src/common/extenders/IExtender.ts
+++ b/framework/core/js/src/common/extenders/IExtender.ts
@@ -5,6 +5,6 @@ export interface IExtensionModule {
  exports: unknown;
 }

-export default interface IExtender {
-  extend(app: Application, extension: IExtensionModule): void;
+export default interface IExtender<App = Application> {
+  extend(app: App, extension: IExtensionModule): void;
 }
--- a/framework/core/src/Group/GroupRepository.php
+++ b/framework/core/src/Group/GroupRepository.php
@@ -41,6 +41,11 @@ class GroupRepository
        return $this->scopeVisibleTo($query, $actor)->firstOrFail();
    }

+    public function queryVisibleTo(User $actor = null)
+    {
+        return $this->scopeVisibleTo($this->query(), $actor);
+    }
+
    /**
     * Scope a query to only include records that are visible to a user.
     *
--- a/php-packages/phpstan/src/Extender/Resolver.php
+++ b/php-packages/phpstan/src/Extender/Resolver.php
@@ -68,6 +68,8 @@ class Resolver
    }

    /**
+     * Retrieves all extenders from a given `extend.php` file.
+     *
     * @return Extender[]
     * @throws ParserErrorsException
     * @throws \Exception
@@ -90,7 +92,22 @@ class Resolver
                if ($expression instanceof Array_) {
                    foreach ($expression->items as $item) {
                        if ($item->value instanceof MethodCall) {
-                            $extenders[] = $this->resolveExtender($item->value);
+                            // Conditional extenders
+                            if ($item->value->name->toString() === 'whenExtensionEnabled') {
+                                $conditionalExtenders = $item->value->args[1] ?? null;
+
+                                if ($conditionalExtenders->value instanceof Array_) {
+                                    foreach ($conditionalExtenders->value->items as $conditionalExtender) {
+                                        if ($conditionalExtender->value instanceof MethodCall) {
+                                            $extenders[] = $this->resolveExtender($conditionalExtender->value);
+                                        }
+                                    }
+                                }
+                            }
+                            // Normal extenders
+                            else {
+                                $extenders[] = $this->resolveExtender($item->value);
+                            }
                        }
                    }
                }