Allow categories: true to make feeds for all categories

README.md

@@ -153,6 +153,13 @@ feed:
     - updates
 ```
 
+Or, to generate a feed for all categories:
+
+```yml
+feed:
+  categories: true
+```
+
 ## Posts limit
 
 By default the plugin limits the number of posts in the feed to 10. Simply define a new limit in your config:
@@ -193,6 +200,16 @@ feed:
         - updates
 ```
 
+Or pass `categories: true` to generate a feed for all categories:
+
+```yml
+feed:
+  collections:
+    changes:
+      path: "/changes.atom"
+      categories: true
+```
+
 ## Excerpt Only flag
 
 Optional flag `excerpt_only` allows you to exclude post content from the Atom feed. Default value is `false` for backward compatibility.

lib/jekyll-feed/generator.rb

@@ -69,7 +69,16 @@ def collections
 
       @collections = normalize_posts_meta(@collections)
       @collections.each_value do |meta|
-        meta["categories"] = (meta["categories"] || []).to_set
+        meta_categories = meta["categories"]
+        for_collection = case meta_categories
+                         when Array
+                           meta_categories
+                         when true
+                           @site.categories.keys
+                         else
+                           []
+                         end
+        meta["categories"] = for_collection.to_set
       end
 
       @collections

spec/jekyll-feed_spec.rb

@@ -423,6 +423,20 @@ def to_s
       end
     end
 
+    context "with top-level post categories (using true to mean all)" do
+      let(:overrides) do
+        {
+          "feed" => { "categories" => true }
+        }
+      end
+
+      it "outputs feeds for all categories" do
+        site.categories.each_key do |category|
+          expect(Pathname.new(dest_dir("feed/#{category}.xml"))).to exist
+        end
+      end
+    end
+
     context "with collection-level post categories" do
       let(:overrides) do
         {