FIX: invalid user locale when accepting group membership

If, for whatever reasons, the user's locale is "blank" and an admin is accepting their group membership request, there will be an error because we're generating posts with the locale of recipient.

In order to fix this, we now use the `user.effective_locale` which takes care of multiple things, including returning the default locale when the user's locale is blank.

Internal ref - t/132347

app/controllers/groups_controller.rb

@@ -484,10 +484,12 @@ class GroupsController < ApplicationController
     request_topic =
       Topic.find_by(
         title:
-          (
-            I18n.t "groups.request_membership_pm.title", group_name: group.name, locale: user.locale
+          I18n.t(
+            "groups.request_membership_pm.title",
+            group_name: group.name,
+            locale: user.effective_locale,
           ),
-        archetype: "private_message",
+        archetype: Archetype.private_message,
         user_id: user.id,
       )
 
@@ -506,7 +508,11 @@ class GroupsController < ApplicationController
         post_type: Post.types[:regular],
         topic_id: request_topic.id,
         raw:
-          (I18n.t "groups.request_accepted_pm.body", group_name: group.name, locale: user.locale),
+          I18n.t(
+            "groups.request_accepted_pm.body",
+            group_name: group.name,
+            locale: user.effective_locale,
+          ),
         reply_to_post_number: 1,
         target_usernames: user.username,
         skip_validations: true,

app/models/discourse_connect.rb

@@ -353,7 +353,7 @@ class DiscourseConnect < DiscourseConnectBase
       user.name = name || User.suggest_name(username.blank? ? email : username)
     end
 
-    if locale_force_update && SiteSetting.allow_user_locale && locale &&
+    if locale_force_update && SiteSetting.allow_user_locale && locale.present? &&
          LocaleSiteSetting.valid_value?(locale)
       user.locale = locale
     end

app/services/badge_granter.rb

@@ -102,7 +102,7 @@ class BadgeGranter
         user_id: user.id,
         badge_id: badge.id,
       )
-      notification = send_notification(user.id, user.username, user.locale, badge)
+      notification = send_notification(user.id, user.username, user.effective_locale, badge)
 
       DB.exec(<<~SQL, notification_id: notification.id, user_id: user.id, badge_id: badge.id)
         UPDATE user_badges

spec/requests/groups_controller_spec.rb

@@ -2276,7 +2276,7 @@ RSpec.describe GroupsController do
         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}",
+        target_usernames: user.username,
         skip_validations: true,
       ).create!
 
@@ -2312,15 +2312,10 @@ RSpec.describe GroupsController do
       # send the initial request PM
       PostCreator.new(
         other_user,
-        title:
-          (
-            I18n.t "groups.request_membership_pm.title",
-                   group_name: group.name,
-                   locale: other_user.locale
-          ),
+        title: I18n.t("groups.request_membership_pm.title", group_name: group.name, locale: "fr"),
         raw: "*French accent* Please let me in!",
         archetype: Archetype.private_message,
-        target_usernames: "#{user.username}",
+        target_usernames: user.username,
         skip_validations: true,
       ).create!
 
@@ -2346,6 +2341,34 @@ RSpec.describe GroupsController do
         I18n.t("groups.request_accepted_pm.body", group_name: group.name, locale: "fr").strip,
       )
     end
+
+    it "works even though the user has no locale" do
+      other_user.update!(locale: "")
+
+      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: "*Alien accent* Can I join?!",
+        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_not change { Topic.count }
+
+      expect(topic.posts.count).to eq(2)
+    end
   end
 
   describe "#histories" do