Reload gunicorn when site-icons CSS updates

This starts using webassets for the site-icons.css file inside the base
template so that a cache-busting "version" string is added after the
filename as a query variable (as was already being done with the other
CSS and JS files).

It also creates a new service that's triggered by a "path changed" event
on site-icons.css, which causes gunicorn to reload. This should mean
that whenever the site-icons.css file is updated by the cronjob that
generates it, gunicorn will automatically reload and update the
cache-busting string for the CSS file, causing users' browsers to update
to the newest version.

salt/salt/gunicorn/gunicorn_reloader.path

@@ -0,0 +1,5 @@
+[Path]
+PathChanged=/opt/tildes/static/css/site-icons.css
+
+[Install]
+WantedBy=multi-user.target

salt/salt/gunicorn/gunicorn_reloader.service

@@ -0,0 +1,10 @@
+[Unit]
+Description=gunicorn reloader
+After=network.target
+
+[Service]
+Type=oneshot
+ExecStart=/bin/systemctl reload gunicorn.service
+
+[Install]
+WantedBy=multi-user.target

salt/salt/gunicorn/init.sls

@@ -33,3 +33,27 @@
 gunicorn.socket:
   service.running:
     - enable: True
+
+# Set up the gunicorn_reloader service, which reloads gunicorn whenever certain files
+# are changed (such as static files, to update the cache-busting strings)
+/etc/systemd/system/gunicorn_reloader.service:
+  file.managed:
+    - source: salt://gunicorn/gunicorn_reloader.service
+    - user: root
+    - group: root
+    - mode: 644
+    - require_in:
+      - service: gunicorn_reloader.path
+
+/etc/systemd/system/gunicorn_reloader.path:
+  file.managed:
+    - source: salt://gunicorn/gunicorn_reloader.path
+    - user: root
+    - group: root
+    - mode: 644
+    - require_in:
+      - service: gunicorn_reloader.path
+
+gunicorn_reloader.path:
+  service.running:
+    - enable: True

tildes/tildes/__init__.py

@@ -33,6 +33,7 @@ def main(global_config: Dict[str, str], **settings: str) -> PrefixMiddleware:
     config.add_webasset("javascript", Bundle(output="js/tildes.js"))
     config.add_webasset("javascript-third-party", Bundle(output="js/third_party.js"))
     config.add_webasset("css", Bundle(output="css/tildes.css"))
+    config.add_webasset("site-icons-css", Bundle(output="css/site-icons.css"))
 
     config.scan("tildes.views")
 

tildes/tildes/templates/base.jinja2

@@ -37,7 +37,9 @@
   {% assets "css" %}
   <link rel="stylesheet" href="{{ ASSET_URL }}">
   {% endassets %}
-  <link rel="stylesheet" href="/css/site-icons.css">
+  {% assets "site-icons-css" %}
+  <link rel="stylesheet" href="{{ ASSET_URL }}">
+  {% endassets %}
 
   {# Favicons and other data for "pinning" the site on various platforms #}
   <link rel="icon" type="image/png" href="/favicon-16x16.png" sizes="16x16">