Don't create an empty <summary> in Atom feeds (gorilla#83)

When creating an AtomEntry from an Item, only set Summary if
item.Description is non-empty, like we already do for Content.

Currently we always emit a `<summary>` element, even if the item has a
non-empty `<content>` element. Having an empty `<summary>` in this case
may
be confusing for feed consumers.

The Atom RFC explicitly says that a `<summary>` is not required in
general.
(There are a couple special cases where it is required, but they aren't
relevant here.)

https://tools.ietf.org/html/rfc4287#section-4.1.1.1

Fixes gorilla#82

Co-authored-by: Corey Daley <cdaley@redhat.com>

atom.go

@@ -89,8 +89,6 @@ type Atom struct {
 
 func newAtomEntry(i *Item) *AtomEntry {
 	id := i.Id
-	// assume the description is html
-	s := &AtomSummary{Content: i.Description, Type: "html"}
 
 	if len(id) == 0 {
 		// if there's no id set, try to create one, either from data or just a uuid
@@ -119,7 +117,11 @@ func newAtomEntry(i *Item) *AtomEntry {
 		Links:   []AtomLink{{Href: i.Link.Href, Rel: link_rel, Type: i.Link.Type}},
 		Id:      id,
 		Updated: anyTimeFormat(time.RFC3339, i.Updated, i.Created),
-		Summary: s,
+	}
+
+	// if there's a description, assume it's html
+	if len(i.Description) > 0 {
+		x.Summary = &AtomSummary{Content: i.Description, Type: "html"}
 	}
 
 	// if there's a content, assume it's html

feed_test.go

@@ -59,6 +59,13 @@ var atomOutput = `<?xml version="1.0" encoding="UTF-8"?><feed xmlns="http://www.
     <link href="http://example.com/strings" rel="alternate"></link>
     <summary type="html">How to use things like %s, %v, %d, etc.</summary>
   </entry>
+  <entry>
+    <title>Go Proverb #1</title>
+    <updated>2013-01-16T21:52:35-05:00</updated>
+    <id>tag:go-proverbs.github.io,2013-01-16:/</id>
+    <content type="html">Don&#39;t communicate by sharing memory, share memory by communicating.</content>
+    <link href="https://go-proverbs.github.io/" rel="alternate"></link>
+  </entry>
 </feed>`
 
 var rssOutput = `<?xml version="1.0" encoding="UTF-8"?><rss version="2.0" xmlns:content="http://purl.org/rss/1.0/modules/content/">
@@ -103,6 +110,13 @@ var rssOutput = `<?xml version="1.0" encoding="UTF-8"?><rss version="2.0" xmlns:
       <description>How to use things like %s, %v, %d, etc.</description>
       <pubDate>Wed, 16 Jan 2013 21:52:35 -0500</pubDate>
     </item>
+    <item>
+      <title>Go Proverb #1</title>
+      <link>https://go-proverbs.github.io/</link>
+      <description></description>
+      <content:encoded><![CDATA[Don't communicate by sharing memory, share memory by communicating.]]></content:encoded>
+      <pubDate>Wed, 16 Jan 2013 21:52:35 -0500</pubDate>
+    </item>
   </channel>
 </rss>`
 
@@ -154,6 +168,13 @@ var jsonOutput = `{
       "title": "String formatting in Go",
       "summary": "How to use things like %s, %v, %d, etc.",
       "date_published": "2013-01-16T21:52:35-05:00"
+    },
+    {
+      "id": "",
+      "url": "https://go-proverbs.github.io/",
+      "title": "Go Proverb #1",
+      "content_html": "Don't communicate by sharing memory, share memory by communicating.",
+      "date_published": "2013-01-16T21:52:35-05:00"
     }
   ]
 }`
@@ -209,6 +230,12 @@ func TestFeed(t *testing.T) {
 			Link:        &Link{Href: "http://example.com/strings"},
 			Description: "How to use things like %s, %v, %d, etc.",
 			Created:     now,
+		},
+		{
+			Title:   "Go Proverb #1",
+			Link:    &Link{Href: "https://go-proverbs.github.io/"},
+			Content: "Don't communicate by sharing memory, share memory by communicating.",
+			Created: now,
 		}}
 
 	atom, err := feed.ToAtom()
@@ -273,35 +300,30 @@ var atomOutputSorted = `<?xml version="1.0" encoding="UTF-8"?><feed xmlns="http:
     <updated>2013-01-18T21:52:35-05:00</updated>
     <id>tag:jmoiron.net,2013-01-18:/blog/limiting-concurrency-in-go/</id>
     <link href="http://jmoiron.net/blog/limiting-concurrency-in-go/" rel="alternate"></link>
-    <summary type="html"></summary>
   </entry>
   <entry>
     <title>Logic-less Template Redux</title>
     <updated>2013-01-17T21:52:35-05:00</updated>
     <id>tag:jmoiron.net,2013-01-17:/blog/logicless-template-redux/</id>
     <link href="http://jmoiron.net/blog/logicless-template-redux/" rel="alternate"></link>
-    <summary type="html"></summary>
   </entry>
   <entry>
     <title>Idiomatic Code Reuse in Go</title>
     <updated>2013-01-17T09:52:35-05:00</updated>
     <id>tag:jmoiron.net,2013-01-17:/blog/idiomatic-code-reuse-in-go/</id>
     <link href="http://jmoiron.net/blog/idiomatic-code-reuse-in-go/" rel="alternate"></link>
-    <summary type="html"></summary>
   </entry>
   <entry>
     <title>Never Gonna Give You Up Mp3</title>
     <updated>2013-01-17T07:52:35-05:00</updated>
     <id>tag:example.com,2013-01-17:/RickRoll.mp3</id>
     <link href="http://example.com/RickRoll.mp3" rel="alternate"></link>
-    <summary type="html"></summary>
   </entry>
   <entry>
     <title>String formatting in Go</title>
     <updated>2013-01-16T21:52:35-05:00</updated>
     <id>tag:example.com,2013-01-16:/strings</id>
     <link href="http://example.com/strings" rel="alternate"></link>
-    <summary type="html"></summary>
   </entry>
 </feed>`