Avoid custom code for linebreaks

We want newlines to be treated as hard breaks; like StackOverflow and
GitHub flavored Markdown do. Previously this was done with a custom
hack, let's use an officially supported extension to our markdown
renderer instead.

Fixes knatten/cppquiz23#257 and helps with #345

quiz/templatetags/quiz_extras.py

@@ -27,21 +27,11 @@ def standard_ref(text):
     regex = re.compile('§(' + section_name + possible_paragraph + ')')
     return re.sub(regex, format_reference, text)
 
-
-def custom_linebreaks(text):
-    return (text
-            .replace("\n", "<br />")
-            .replace("</p><br />", "</p>")
-            .replace("<br /><p>", "<p>")
-            .replace("</pre><br />", "</pre>"))
-
-
 @register.filter(needs_autoescape=True)
 def to_html(text, autoescape=None):
     return mark_safe(
         standard_ref(
-            custom_linebreaks(
-                markdown.markdown(text))))
+            markdown.markdown(text, extensions=['nl2br'])))
 
 
 @register.filter()

requirements.in

@@ -1,5 +1,6 @@
 Django>=4.1,<5
 Markdown
+pymdown-extensions
 mock
 parameterized
 tweepy

requirements.txt

@@ -27,7 +27,9 @@ idna==3.7
 lxml==5.2.2
     # via splinter
 markdown==3.6
-    # via -r requirements.in
+    # via
+    #   -r requirements.in
+    #   pymdown-extensions
 mock==5.1.0
     # via -r requirements.in
 oauthlib==3.2.2
@@ -42,10 +44,14 @@ pip-tools==7.4.1
     # via -r requirements.in
 pycodestyle==2.12.0
     # via autopep8
+pymdown-extensions==10.9
+    # via -r requirements.in
 pyproject-hooks==1.1.0
     # via
     #   build
     #   pip-tools
+pyyaml==6.0.1
+    # via pymdown-extensions
 requests==2.32.3
     # via
     #   requests-oauthlib
@@ -54,7 +60,7 @@ requests-oauthlib==1.3.1
     # via tweepy
 splinter[django]==0.21.0
     # via -r requirements.in
-sqlparse==0.5.0
+sqlparse==0.5.1
     # via django
 tweepy==4.14.0
     # via -r requirements.in