Add "html_excerpts" flag to allow Atom <summary> tags to contain HTML

README.md

@@ -207,6 +207,17 @@ feed:
 The same flag can be used directly in post file. It will disable `<content>` tag for selected post.
 Settings in post file have higher priority than in config file.
 
+## HTML Excerpts flag
+
+By default, the `<summary>` portion of the feed—containing the post's excerpt or description—will be stripped of all HTML, and will have all its whitespace normalized. The optional flag `html_excerpts` turns that behaviour off, allowing your excerpts to contain full HTML content.
+
+```yml
+feed:
+  html_excerpts: true
+```
+
+This is useful in feeds where the excerpts have more complex content or formatting, such as when the post's `description` and `excerpt` front matter options are not set, causing Jekyll to [use the entire first paragraph of the post as the excerpt](https://jekyllrb.com/docs/posts/#post-excerpts).
+
 ## Tags
 
 To automatically generate feeds for each tag you apply to your posts you can add a tags setting to your config:

lib/jekyll-feed/feed.xml

@@ -96,7 +96,11 @@
 
       {% assign post_summary = post.description | default: post.excerpt %}
       {% if post_summary and post_summary != empty %}
-        <summary type="html"><![CDATA[{{ post_summary | strip_html | normalize_whitespace }}]]></summary>
+        {% if site.feed.html_excerpts %}
+          <summary type="html"><![CDATA[{{ post_summary | strip }}]]></summary>
+        {% else %}
+          <summary type="html"><![CDATA[{{ post_summary | strip_html | normalize_whitespace }}]]></summary>
+        {% endif %}
       {% endif %}
 
       {% assign post_image = post.image.path | default: post.image %}

spec/jekyll-feed_spec.rb

@@ -162,6 +162,34 @@
       expect(post.summary).to be_nil
     end
 
+    it "strips HTML in summaries by default" do
+      post = feed.items.detect { |item| item.title.content == "Pre" }
+      expect(post).to_not be_nil
+      expect(post.summary.content).to_not match "<pre>"
+    end
+
+    it "normalizes whitespace in summaries by default" do
+      post = feed.items.detect { |item| item.title.content == "Pre" }
+      expect(post).to_not be_nil
+      expect(post.summary.content).to_not match "\n"
+    end
+
+    context "with feed.html_excerpts set" do
+      let(:overrides) { { "feed" => { "html_excerpts" => true } } }
+
+      it "doesn't strip HTML in summaries" do
+        post = feed.items.detect { |item| item.title.content == "Pre" }
+        expect(post).to_not be_nil
+        expect(post.summary.content).to match "<pre>"
+      end
+
+      it "doesn't normalize whitespace in summaries" do
+        post = feed.items.detect { |item| item.title.content == "Pre" }
+        expect(post).to_not be_nil
+        expect(post.summary.content).to match "\n"
+      end
+    end
+
     context "with site.lang set" do
       lang = "en_US"
       let(:overrides) { { "lang" => lang } }