From 6a68ba147b0d7812e591f20936c1571f16043e9a Mon Sep 17 00:00:00 2001
From: Isaac Janzen <isaac.janzen@discourse.org>
Date: Thu, 16 Mar 2023 14:09:22 -0500
Subject: [PATCH] FIX: Use tag-intersection route when building more_topics_url
 from tag-intersection

---
 app/controllers/tags_controller.rb    | 12 ++++++++++--
 spec/requests/tags_controller_spec.rb | 18 ++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/app/controllers/tags_controller.rb b/app/controllers/tags_controller.rb
index 5604b401d2..a90a23ce94 100644
--- a/app/controllers/tags_controller.rb
+++ b/app/controllers/tags_controller.rb
@@ -102,8 +102,13 @@ class TagsController < ::ApplicationController
   Discourse.filters.each do |filter|
     define_method("show_#{filter}") do
       @tag_id = params[:tag_id].force_encoding("UTF-8")
-      @additional_tags =
-        params[:additional_tag_ids].to_s.split("/").map { |t| t.force_encoding("UTF-8") }
+      if params[:additional_tag_ids]
+        @additional_tags = params[:additional_tag_ids].to_s.split("/")
+      elsif params[:tags]
+        # Set additional tags to all passed tags excluding the primary tag (tag_id)
+        @additional_tags = params[:tags].reject { |t| t == params[:tag_id] }
+      end
+      @additional_tags = @additional_tags&.map { |t| t.force_encoding("UTF-8") }
 
       list_opts = build_topic_list_options
       @list = nil
@@ -483,6 +488,9 @@ class TagsController < ::ApplicationController
   def url_method(opts = {})
     if opts[:category_slug_path_with_id]
       "tag_category_#{action_name}_path"
+      # expect tag intersection if multiple tags are present
+    elsif opts[:tags] && opts[:tags].length > 1
+      "tag_intersection_path"
     else
       "tag_#{action_name}_path"
     end
diff --git a/spec/requests/tags_controller_spec.rb b/spec/requests/tags_controller_spec.rb
index 63b60c5c31..8656675993 100644
--- a/spec/requests/tags_controller_spec.rb
+++ b/spec/requests/tags_controller_spec.rb
@@ -392,6 +392,24 @@ RSpec.describe TagsController do
         end
       end
     end
+
+    context "with a tag intersection" do
+      it "should generate a tag intersection `load_more_topic` url" do
+        tag = Fabricate(:tag)
+        tag_2 = Fabricate(:tag)
+
+        # Create topics with both tags included
+        3.times { Fabricate(:topic, tags: [tag, tag_2]) }
+
+        sign_in(admin)
+        get "/tags/intersection/#{tag.name}/#{tag_2.name}.json?per_page=2"
+
+        expect(response.status).to eq(200)
+        expect(response.parsed_body["topic_list"]["more_topics_url"]).to eq(
+          "/tags/intersection/#{tag.name}/#{tag_2.name}?match_all_tags=true&page=1&per_page=2&tags%5B%5D=#{tag.name}&tags%5B%5D=#{tag_2.name}",
+        )
+      end
+    end
   end
 
   describe "#show" do