Allow generating empty feeds (#2850)

This enables blogs to be setup that people can subscribe to before the
first post is published.

Author: senekor

Diff for: components/site/src/feeds.rs

@@ -36,11 +36,6 @@ pub fn render_feeds(
 ) -> Result<Option<Vec<String>>> {
     let mut pages = all_pages.into_iter().filter(|p| p.meta.date.is_some()).collect::<Vec<_>>();
 
-    // Don't generate a feed if none of the pages has a date
-    if pages.is_empty() {
-        return Ok(None);
-    }
-
     pages.par_sort_unstable_by(|a, b| {
         let ord = b.meta.datetime.unwrap().cmp(&a.meta.datetime.unwrap());
         if ord == Ordering::Equal {
@@ -51,15 +46,14 @@ pub fn render_feeds(
     });
 
     let mut context = Context::new();
-    context.insert(
-        "last_updated",
-        pages
-            .iter()
-            .filter_map(|page| page.meta.updated.as_ref())
-            .chain(pages[0].meta.date.as_ref())
-            .max() // I love lexicographically sorted date strings
-            .unwrap(), // Guaranteed because of pages[0].meta.date
-    );
+    if let Some(last_updated) = pages
+        .iter()
+        .filter_map(|page| page.meta.updated.as_ref())
+        .chain(pages.first().and_then(|p| p.meta.date.as_ref()))
+        .max()
+    {
+        context.insert("last_updated", &last_updated);
+    }
     let library = site.library.read().unwrap();
     // limit to the last n elements if the limit is set; otherwise use all.
     let num_entries = site.config.feed_limit.unwrap_or(pages.len());

Diff for: components/templates/src/builtins/atom.xml

@@ -17,7 +17,7 @@
       {%- endif -%}
     "/>
     <generator uri="https://www.getzola.org/">Zola</generator>
-    <updated>{{ last_updated | date(format="%+") }}</updated>
+    {% if last_updated is defined %}<updated>{{ last_updated | date(format="%+") }}</updated>{% endif %}
     <id>{{ feed_url | safe }}</id>
     {%- for page in pages %}
     <entry xml:lang="{{ page.lang }}">

Diff for: components/templates/src/builtins/rss.xml

@@ -17,7 +17,7 @@
       <generator>Zola</generator>
       <language>{{ lang }}</language>
       <atom:link href="{{ feed_url | safe }}" rel="self" type="application/rss+xml"/>
-      <lastBuildDate>{{ last_updated | date(format="%a, %d %b %Y %H:%M:%S %z") }}</lastBuildDate>
+      {% if last_updated is defined %}<lastBuildDate>{{ last_updated | date(format="%a, %d %b %Y %H:%M:%S %z") }}</lastBuildDate>{% endif %}
       {%- for page in pages %}
       <item>
           <title>{{ page.title }}</title>