FEATURE: Add category ignore list for GitHub linkbacks (discourse#35921)

Sometimes you have categories where posts mention GitHub URLs but you
don't actually want linkback comments posted to GitHub — think
AI-generated summaries or automated reports that reference commits but
would just create noise on the issue tracker.

This adds a `github_linkback_ignored_categories` site setting that lets
admins specify which categories should be skipped entirely when
processing linkbacks. Posts in those categories won't trigger any GitHub
comments, keeping things clean.

To make this work nicely, the setting uses the `category_list` type
which gives you a proper category picker in the admin UI rather than
having to type raw IDs. This required extending core's `_map`
metaprogramming helper (which previously only worked with `group_list`
settings) to also handle `category_list` — so now any `category_list`
setting automatically gets a `_map` variant that returns an array of
integers, just like group settings do.

Screenshot of new setting:
<img width="774" height="116" alt="discourse-github-ignore-cat"
src="https://github.com/user-attachments/assets/dd9a3c85-7f01-47c6-b1b7-fe6ef120ab8b"
/>

Ref: /t/141863

---------

Co-authored-by: zogstrip <regis@hanol.fr>

Author: ducks

lib/site_setting_extension.rb

@@ -963,10 +963,10 @@ def setup_methods(name)
       end
     end
 
-    # Any group_list setting, e.g. personal_message_enabled_groups, will have
-    # a getter defined with _map on the end, e.g. personal_message_enabled_groups_map,
-    # to avoid having to manually split and convert to integer for these settings.
-    if type_supervisor.get_type(name) == :group_list
+    # Any group_list or category_list setting will have a getter defined with _map
+    # on the end, e.g. personal_message_enabled_groups_map, to avoid having to
+    # manually split and convert to integer for these settings.
+    if %i[group_list category_list].include?(type_supervisor.get_type(name))
       define_singleton_method("#{clean_name}_map") do
         self.public_send(clean_name).to_s.split("|").map(&:to_i)
       end

plugins/discourse-github/app/lib/github_linkback.rb

@@ -20,6 +20,8 @@ def initialize(post)
   end
 
   def should_enqueue?
+    return false if ignored_category?
+
     !!(
       SiteSetting.github_linkback_enabled? && SiteSetting.enable_discourse_github_plugin? &&
         @post.present? && @post.post_type == Post.types[:regular] && @post.raw =~ /github\.com/ &&
@@ -125,6 +127,12 @@ def self.field_for(url)
 
   private
 
+  def ignored_category?
+    return false if @post&.topic&.category_id.blank?
+
+    SiteSetting.github_linkback_ignored_categories_map.include?(@post.topic.category_id)
+  end
+
   def post_pr_or_issue(link, type)
     pr_or_issue_number = link.pr_number || link.issue_number
     github_url =

plugins/discourse-github/config/settings.yml

@@ -13,6 +13,9 @@ discourse_github:
   github_linkback_maximum_links:
     default: 25
     min: 1
+  github_linkback_ignored_categories:
+    default: ""
+    type: category_list
   github_badges_enabled:
     default: false
   github_badges_repos:

plugins/discourse-github/spec/lib/github_linkback_spec.rb

@@ -109,6 +109,45 @@
         expect(GithubLinkback.new(unlisted_post).should_enqueue?).to eq(false)
       end
     end
+
+    describe "ignored categories" do
+      fab!(:category)
+      fab!(:post_in_category) do
+        topic = Fabricate(:topic, category:)
+        Fabricate(:post, topic:, raw: "https://github.com/discourse/discourse/commit/abc123")
+      end
+
+      before { SiteSetting.github_linkback_enabled = true }
+
+      it "doesn't enqueue posts in ignored categories" do
+        SiteSetting.github_linkback_ignored_categories = category.id.to_s
+        expect(GithubLinkback.new(post_in_category).should_enqueue?).to eq(false)
+      end
+
+      it "enqueues posts in non-ignored categories" do
+        other_category = Fabricate(:category)
+        SiteSetting.github_linkback_ignored_categories = other_category.id.to_s
+        expect(GithubLinkback.new(post_in_category).should_enqueue?).to eq(true)
+      end
+
+      it "handles multiple ignored categories" do
+        other_category = Fabricate(:category)
+        SiteSetting.github_linkback_ignored_categories = "#{category.id}|#{other_category.id}"
+        expect(GithubLinkback.new(post_in_category).should_enqueue?).to eq(false)
+      end
+
+      it "enqueues when ignored categories setting is empty" do
+        SiteSetting.github_linkback_ignored_categories = ""
+        expect(GithubLinkback.new(post_in_category).should_enqueue?).to eq(true)
+      end
+
+      it "enqueues posts without a category" do
+        SiteSetting.github_linkback_ignored_categories = category.id.to_s
+        uncategorized_post =
+          Fabricate(:post, raw: "https://github.com/discourse/discourse/commit/abc123")
+        expect(GithubLinkback.new(uncategorized_post).should_enqueue?).to eq(true)
+      end
+    end
   end
 
   describe "#github_links" do

spec/lib/site_setting_extension_spec.rb

@@ -1392,6 +1392,11 @@ def self.translate_names?
       expect(SiteSetting.personal_message_enabled_groups_map).to eq([1, 2])
     end
 
+    it "handles splitting category_list settings" do
+      SiteSetting.digest_suppress_categories = "3|4"
+      expect(SiteSetting.digest_suppress_categories_map).to eq([3, 4])
+    end
+
     it "handles splitting compact list settings" do
       SiteSetting.markdown_linkify_tlds = "com|net"
       expect(SiteSetting.markdown_linkify_tlds_map).to eq(%w[com net])