FEATURE: show category-to-tag relationships on tags index page

app/assets/javascripts/discourse/components/tag-list.js.es6

@@ -0,0 +1,21 @@
+export default Ember.Component.extend({
+  classNameBindings: [':tag-list', 'categoryClass'],
+
+  sortedTags: Ember.computed.sort('tags', 'sortProperties'),
+
+  title: function() {
+    if (this.get('titleKey')) { return I18n.t(this.get('titleKey')); }
+  }.property('titleKey'),
+
+  category: function() {
+    if (this.get('categoryId')) {
+      return Discourse.Category.findById(this.get('categoryId'));
+    }
+  }.property('categoryId'),
+
+  categoryClass: function() {
+    if (this.get('category')) {
+      return "tag-list-" + this.get('category.fullSlug');
+    }
+  }.property('category')
+});

app/assets/javascripts/discourse/controllers/tags-index.js.es6

@@ -1,8 +1,6 @@
 export default Ember.Controller.extend({
   sortProperties: ['count:desc', 'id'],
 
-  sortedTags: Ember.computed.sort('model', 'sortProperties'),
-
   actions: {
     sortByCount() {
       this.set('sortProperties', ['count:desc', 'id']);

app/assets/javascripts/discourse/templates/components/tag-list.hbs

@@ -0,0 +1,13 @@
+{{#if title}}
+  <h3>{{title}}</h3>
+{{/if}}
+{{#if category}}
+  {{category-title-link category=category}}
+{{/if}}
+{{#each sortedTags as |tag|}}
+  <div class='tag-box'>
+    {{discourse-tag tag.id}} <span class='tag-count'>x {{tag.count}}</span>
+  </div>
+{{/each}}
+<div class="clearfix" />
+<hr/>

app/assets/javascripts/discourse/templates/tags/index.hbs

@@ -2,18 +2,17 @@
   {{discourse-banner user=currentUser banner=site.banner}}
 </div>
 
-<h2>{{i18n "tagging.all_tags"}}</h2>
+<h2>{{i18n "tagging.tags"}}</h2>
 
 <div class='tag-sort-options'>
   {{i18n "tagging.sort_by"}}
   <a {{action "sortByCount"}}>{{i18n "tagging.sort_by_count"}}</a>
   <a {{action "sortById"}}>{{i18n "tagging.sort_by_name"}}</a>
 </div>
+<div class="clearfix" />
 
-<div class='tag-list'>
-  {{#each sortedTags as |tag|}}
-    <div class='tag-box'>
-      {{discourse-tag tag.id}} <span class='tag-count'>x {{tag.count}}</span>
-    </div>
-  {{/each}}
-</div>
+{{#each model.extras.categories as |category|}}
+  {{tag-list tags=category.tags sortProperties=sortProperties categoryId=category.id}}
+{{/each}}
+
+{{tag-list tags=model sortProperties=sortProperties titleKey="tagging.all_tags"}}

app/assets/stylesheets/common/base/tagging.scss

@@ -8,6 +8,10 @@
   margin-top: 2em;
 }
 
+#list-area .tag-list h3 {
+  margin-bottom: 20px;
+}
+
 .tag-box {
   display: inline-block;
   width: 300px;
@@ -180,8 +184,11 @@ header .discourse-tag {color: $tag-color !important; }
   padding-top: 2px;
 }
 
-.tag-sort-options a {
-  text-decoration: underline;
+.tag-sort-options {
+  margin-bottom: 20px;
+  a {
+    text-decoration: underline;
+  }
 }
 
 .autocomplete {

app/controllers/tags_controller.rb

@@ -12,15 +12,23 @@ class TagsController < ::ApplicationController
   before_filter :set_category_from_params, except: [:index, :update, :destroy, :tag_feed, :search, :notifications, :update_notifications]
 
   def index
+    categories = Category.where("id in (select category_id from category_tags)")
+                         .where("id in (?)", guardian.allowed_category_ids)
+                         .preload(:tags)
+    category_tag_counts = categories.map { |c| {id: c.id, tags: self.class.tag_counts_json(Tag.category_tags_by_count_query(c, limit: 300).count)} }
+
     tag_counts = self.class.tags_by_count(guardian, limit: 300).count
-    @tags = tag_counts.map {|t, c| { id: t, text: t, count: c } }
+    @tags = self.class.tag_counts_json(tag_counts)
 
     respond_to do |format|
       format.html do
         render :index
       end
       format.json do
-        render json: { tags: @tags }
+        render json: {
+          tags: @tags,
+          extras: { categories: category_tag_counts }
+        }
       end
     end
   end
@@ -154,6 +162,10 @@ class TagsController < ::ApplicationController
       guardian.filter_allowed_categories(Tag.tags_by_count_query(opts))
     end
 
+    def self.tag_counts_json(tag_counts)
+      tag_counts.map {|t, c| { id: t, text: t, count: c } }
+    end
+
     def set_category_from_params
       slug_or_id = params[:category]
       return true if slug_or_id.nil?

app/models/tag.rb

@@ -15,6 +15,11 @@ class Tag < ActiveRecord::Base
     q
   end
 
+  def self.category_tags_by_count_query(category, opts={})
+    tags_by_count_query(opts).where("tags.id in (select tag_id from category_tags where category_id = ?)", category.id)
+                             .where("topics.category_id = ?", category.id)
+  end
+
   def self.top_tags(limit_arg=nil)
     self.tags_by_count_query(limit: limit_arg || SiteSetting.max_tags_in_filter_list)
         .count