UX: Group membership PMs thread

app/controllers/groups_controller.rb

@@ -457,6 +457,14 @@ def handle_membership_request
     user = User.find_by(id: params[:user_id])
     raise Discourse::InvalidParameters.new(:user_id) if user.blank?
 
+    # find original membership request PM
+    request_topic =
+      Topic.find_by(
+        title: I18n.t("groups.request_membership_pm.title", group_name: group.name),
+        archetype: "private_message",
+        user_id: user.id,
+      )
+
     ActiveRecord::Base.transaction do
       if params[:accept]
         group.add(user)
@@ -469,9 +477,10 @@ def handle_membership_request
     if params[:accept]
       PostCreator.new(
         current_user,
-        title: I18n.t("groups.request_accepted_pm.title", group_name: group.name),
+        post_type: Post.types[:regular],
+        topic_id: request_topic.id,
         raw: I18n.t("groups.request_accepted_pm.body", group_name: group.name),
-        archetype: Archetype.private_message,
+        reply_to_post_number: 1,
         target_usernames: user.username,
         skip_validations: true,
       ).create!

config/locales/server.en.yml

@@ -638,7 +638,6 @@ en:
     request_membership_pm:
       title: "Membership Request for @%{group_name}"
     request_accepted_pm:
-      title: "You've been accepted into @%{group_name}"
       body: |
         Your request to enter @%{group_name} has been accepted and you are now a member.
 

spec/requests/groups_controller_spec.rb

@@ -2165,20 +2165,38 @@ def expect_type_to_return_right_groups(type, expected_group_ids)
       sign_in(user)
     end
 
-    it "sends a private message when accepted" do
+    it "sends a reply to the request membership topic when accepted" do
       GroupRequest.create!(group: group, user: other_user)
+
+      # send the initial request PM
+      PostCreator.new(
+        other_user,
+        title: I18n.t("groups.request_membership_pm.title", group_name: group.name),
+        raw: "*British accent* Please, sir, may I have some group?",
+        archetype: Archetype.private_message,
+        target_usernames: "#{user.username}",
+        skip_validations: true,
+      ).create!
+
+      topic = Topic.last
+
       expect {
         put "/groups/#{group.id}/handle_membership_request.json",
             params: {
               user_id: other_user.id,
               accept: true,
             }
-      }.to change { Topic.count }.by(1).and change { Post.count }.by(1)
+      }.to_not change { Topic.count }
 
-      topic = Topic.last
       expect(topic.archetype).to eq(Archetype.private_message)
-      expect(topic.title).to eq(I18n.t("groups.request_accepted_pm.title", group_name: group.name))
-      expect(topic.first_post.raw).to eq(
+      expect(Topic.first.title).to eq(
+        I18n.t("groups.request_membership_pm.title", group_name: group.name),
+      )
+
+      post = Post.last
+      expect(post.topic_id).to eq(Topic.last.id)
+      expect(topic.posts.count).to eq(2)
+      expect(post.raw).to eq(
         I18n.t("groups.request_accepted_pm.body", group_name: group.name).strip,
       )
     end