DEV: Add auto map from TL -> group site settings in DeprecatedSettings (#24959)

When setting an old TL based site setting in the console e.g.:

SiteSetting.min_trust_level_to_allow_ignore = TrustLevel[3]

We will silently convert this to the corresponding Group::AUTO_GROUP. And vice-versa, when we read the value on the old setting, we will automatically get the lowest trust level corresponding to the lowest auto group for the new setting in the database.

lib/site_settings/deprecated_settings.rb

@@ -35,9 +35,80 @@ module SiteSettings::DeprecatedSettings
     ["min_trust_level_to_allow_ignore", "ignore_allowed_groups", false, "3.3"],
   ]
 
+  OVERRIDE_TL_GROUP_SETTINGS = %w[
+    anonymous_posting_min_trust_level
+    shared_drafts_min_trust_level
+    min_trust_level_for_here_mention
+    approve_unless_trust_level
+    approve_new_topics_unless_trust_level
+    email_in_min_trust
+    min_trust_to_edit_wiki_post
+    allow_uploaded_avatars
+    min_trust_to_create_topic
+    min_trust_to_edit_post
+    min_trust_to_flag_posts
+    tl4_delete_posts_and_topics
+    min_trust_level_to_allow_user_card_background
+    min_trust_level_to_allow_invite
+    min_trust_level_to_allow_ignore
+  ]
+
+  def group_to_tl(old_setting, new_setting)
+    tl_and_staff = is_tl_and_staff_setting?(old_setting)
+
+    valid_auto_groups =
+      self.public_send("#{new_setting}_map") &
+        # We only want auto groups, no actual groups because they cannot be
+        # mapped to TLs.
+        Group.auto_groups_between(tl_and_staff ? :admins : :trust_level_0, :trust_level_4)
+
+    # We don't want to return nil because this could lead to permission holes;
+    # so we return the max available permission in this case.
+    return tl_and_staff ? "admin" : TrustLevel[4] if valid_auto_groups.empty?
+
+    if tl_and_staff
+      valid_auto_groups_excluding_staff_and_admins =
+        valid_auto_groups - [Group::AUTO_GROUPS[:staff], Group::AUTO_GROUPS[:admins]]
+
+      if valid_auto_groups_excluding_staff_and_admins.any?
+        return valid_auto_groups_excluding_staff_and_admins.min - Group::AUTO_GROUPS[:trust_level_0]
+      end
+
+      if valid_auto_groups.include?(Group::AUTO_GROUPS[:staff])
+        "staff"
+      elsif valid_auto_groups.include?(Group::AUTO_GROUPS[:admins])
+        "admin"
+      end
+    else
+      valid_auto_groups.min - Group::AUTO_GROUPS[:trust_level_0]
+    end
+  end
+
+  def tl_to_group(old_setting, val)
+    tl_and_staff = is_tl_and_staff_setting?(old_setting)
+
+    if val == "admin"
+      Group::AUTO_GROUPS[:admins]
+    elsif val == "staff"
+      Group::AUTO_GROUPS[:staff]
+    else
+      if tl_and_staff
+        "#{Group::AUTO_GROUPS[:admins]}|#{Group::AUTO_GROUPS[:staff]}|#{val.to_i + Group::AUTO_GROUPS[:trust_level_0]}"
+      else
+        "#{val.to_i + Group::AUTO_GROUPS[:trust_level_0]}"
+      end
+    end
+  end
+
+  def is_tl_and_staff_setting?(old_setting)
+    SiteSetting.type_supervisor.get_type(old_setting.to_sym) == :enum &&
+      SiteSetting.type_supervisor.get_enum_class(old_setting.to_sym).name ==
+        TrustLevelAndStaffSetting.name
+  end
+
   def setup_deprecated_methods
     SETTINGS.each do |old_setting, new_setting, override, version|
-      unless override
+      if !override
         SiteSetting.singleton_class.public_send(
           :alias_method,
           :"_#{old_setting}",
@@ -45,6 +116,12 @@ module SiteSettings::DeprecatedSettings
         )
       end
 
+      if OVERRIDE_TL_GROUP_SETTINGS.include?(old_setting)
+        define_singleton_method "_group_to_tl_#{old_setting}" do |warn: true|
+          group_to_tl(old_setting, new_setting)
+        end
+      end
+
       define_singleton_method old_setting do |warn: true|
         if warn
           Discourse.deprecate(
@@ -53,10 +130,14 @@ module SiteSettings::DeprecatedSettings
           )
         end
 
-        self.public_send(override ? new_setting : "_#{old_setting}")
+        if OVERRIDE_TL_GROUP_SETTINGS.include?(old_setting)
+          self.public_send("_group_to_tl_#{old_setting}")
+        else
+          self.public_send(override ? new_setting : "_#{old_setting}")
+        end
       end
 
-      unless override
+      if !override
         SiteSetting.singleton_class.public_send(
           :alias_method,
           :"_#{old_setting}?",
@@ -75,7 +156,7 @@ module SiteSettings::DeprecatedSettings
         self.public_send("#{override ? new_setting : "_" + old_setting}?")
       end
 
-      unless override
+      if !override
         SiteSetting.singleton_class.public_send(
           :alias_method,
           :"_#{old_setting}=",
@@ -91,7 +172,14 @@ module SiteSettings::DeprecatedSettings
           )
         end
 
-        self.public_send("#{override ? new_setting : "_" + old_setting}=", val)
+        if OVERRIDE_TL_GROUP_SETTINGS.include?(old_setting)
+          # We want to set both the new group setting here to the equivalent of the
+          # TL, as well as setting the TL value in the DB so they remain in sync.
+          self.public_send("_#{old_setting}=", val)
+          self.public_send("#{new_setting}=", tl_to_group(old_setting, val).to_s)
+        else
+          self.public_send("#{override ? new_setting : "_" + old_setting}=", val)
+        end
       end
     end
   end