Handle undefined variables in rss templates

These templates used to work when using the StrictUndefined undefined
behavior in the jinja2 environment, but in recent releases, this causes
the build to fail. This issue can be seen at
Python-Community-News/Site#38. Using the `is
defined` test results in similar behavior even when `StrictUndefined` is
set, allowing site developers to catch typos or other missing template
context without breaking their rss feeds.

This change also includes a new test and a test fixture to create a
jinja2 environment that can be modified with the scope of a single test.

Author: jonafato

src/render_engine/render_engine_templates/rss2.0.xml

@@ -6,13 +6,13 @@
     <description>{{description}}</description>
     <atom:link href="{{SITE_URL}}" rel="self" type="application/rss+xml" />
 
-{% if language %}<language>{{language}}</language>{% endif %}
-{% if copyright %}<copyright>{{copyright}}</copyright>{% endif %}
-{% if managing_editor %}<managingEditor>{{managing_editor}}</managingEditor>{% endif %}
-{% if web_master %}<webMaster>{{web_master}}</webMaster>{% endif %}
-{% if pub_date %}<pubDate>{{pub_date}}</pubDate>{% endif %}
-{% if last_build_date %}<lastBuildDate>{{last_build_date}}</lastBuildDate>{% endif %}
-{% if categories %}
+{% if language is defined %}<language>{{language}}</language>{% endif %}
+{% if copyright is defined %}<copyright>{{copyright}}</copyright>{% endif %}
+{% if managing_editor is defined %}<managingEditor>{{managing_editor}}</managingEditor>{% endif %}
+{% if web_master is defined %}<webMaster>{{web_master}}</webMaster>{% endif %}
+{% if pub_date is defined %}<pubDate>{{pub_date}}</pubDate>{% endif %}
+{% if last_build_date is defined %}<lastBuildDate>{{last_build_date}}</lastBuildDate>{% endif %}
+{% if categories is defined %}
 {% for category in categories %}
 {% if category['domain'] %}
 <category domain="{{category['domain']}}">{{category}}</category>
@@ -21,14 +21,14 @@
 {% endif %}
 {% endfor %}
 {% endif %}
-{% if generator %}<generator>{{generator}}</generator>{% endif %}
-{% if docs %}<docs>{{docs}}</docs>{% endif %}
-{% if cloud %}
+{% if generator is defined %}<generator>{{generator}}</generator>{% endif %}
+{% if docs is defined %}<docs>{{docs}}</docs>{% endif %}
+{% if cloud is defined %}
 <cloud domain="{{cloud.domain}}" port={{cloud.port}} path="{{cloud.path}}" registerProcedure="{{cloud.register_procedure}}" protocol="{{cloud.protocol}}" />
 {% endif %}
-{% if ttl %}<ttl>{{ttl}}</ttl>{% endif %}
-{% if image %}<image>{{image}}</image>{% endif %}
-{% if comments %}{{comments}}{% endif %}
+{% if ttl is defined %}<ttl>{{ttl}}</ttl>{% endif %}
+{% if image is defined %}<image>{{image}}</image>{% endif %}
+{% if comments is defined %}{{comments}}{% endif %}
 {% for item in pages %}
 {% include 'rss2.0_items.xml' %}
 {% endfor %}

src/render_engine/render_engine_templates/rss2.0_items.xml

@@ -1,16 +1,16 @@
 <item>
-{% if item.title %}<title>{{item.title}}</title>{% endif %}
-{% if item.description %}
+{% if item.title is defined %}<title>{{item.title}}</title>{% endif %}
+{% if item.description is defined %}
   <description><![CDATA[{{item.description}}]]></description>
 {% else %}
   <description><![CDATA[{{item._content|safe }}]]></description>
 {% endif %}
 
-{% if item.enclosure %}
+{% if item.enclosure is defined %}
   <enclosure url="{{item.enclosure}}" length="{{item.enclosure.length}}" type="{{item.enclosure.mime_type}}" />
 {% endif %}
-{% if item.category %}
-  {% if item.category['domain'] %}
+{% if item.category is defined %}
+  {% if item.category is defined['domain'] %}
     <category domain="{{item.category['domain']}}">{{item.category}}</category>
   {% else %}
     <category>{{item.category}}</category>
@@ -19,9 +19,9 @@
     <link>
       {{SITE_URL}}{{item.url_for()}}
     </link>
-{% if item.date_published %}<pubDate>{{item.date_published | to_pub_date }}</pubDate>{% endif %}
-{% if item.guid %}<guid isPermaLink="false">{{item.guid}}</guid>{% endif %}
-{% if item.author %}{{item.author}}{% endif %}
-{% if item.comments %}{{item.comments}}{% endif %}
-{% if item.source %}<source url="{{item.source.url}}">{{item.source}}</source>{% endif %}
+{% if item.date_published is defined %}<pubDate>{{item.date_published | to_pub_date }}</pubDate>{% endif %}
+{% if item.guid is defined %}<guid isPermaLink="false">{{item.guid}}</guid>{% endif %}
+{% if item.author is defined %}{{item.author}}{% endif %}
+{% if item.comments is defined %}{{item.comments}}{% endif %}
+{% if item.source is defined %}<source url="{{item.source.url}}">{{item.source}}</source>{% endif %}
 </item>

tests/conftest.py

@@ -0,0 +1,14 @@
+from jinja2 import Environment, select_autoescape
+import pytest
+
+from render_engine.engine import render_engine_templates_loader
+
+
+@pytest.fixture
+def engine() -> Environment:
+    return Environment(
+        loader=render_engine_templates_loader,
+        autoescape=select_autoescape(["xml"]),
+        lstrip_blocks=True,
+        trim_blocks=True,
+    )

tests/test_feeds.py

@@ -1,5 +1,7 @@
 import pluggy
 
+from jinja2 import StrictUndefined
+
 from render_engine.collection import Collection
 from render_engine.feeds import RSSFeed
 from render_engine.page import Page
@@ -64,4 +66,27 @@ class TestCollection(Collection):
 
     collection = TestCollection()
     print(collection._feed.template)
-    assert "http://localhost:8000//page.html" in collection._feed._render_content(engine=engine)
+    assert "http://localhost:8000//page.html" in collection._feed._render_content(engine=engine)
+
+
+def test_rss_feed_template_with_strictundefined(engine, tmp_path):
+    """Test that the RSS feed template works with the StrictUndefined undefined handler."""
+    tmp_dir = tmp_path / "content"
+    tmp_dir.mkdir()
+    file = tmp_dir / "#"
+    file.write_text("test")
+
+    class TestCollection(Collection):
+        pages = [Page(content_path=file)]
+        Feed = RSSFeed
+
+    collection = TestCollection()
+    engine.undefined = StrictUndefined
+    rendered_content = collection._feed._render_content(
+        engine=engine,
+        SITE_TITLE="Test Site Title",
+        SITE_URL="http://localhost:8000",
+        title="Test Feed Title",
+        description="Test Feed Description",
+    )
+    assert "http://localhost:8000/page.html" in rendered_content