Generate a basic favicon dynamically

app/templates/layout.html

@@ -8,6 +8,7 @@
 <link rel="alternate" title="{{ local_actor.display_name}}'s microblog" type="application/json" href="{{ url_for("json_feed") }}" />
 <link rel="alternate" href="{{ url_for("rss_feed") }}" type="application/rss+xml" title="{{ local_actor.display_name}}'s microblog">
 <link rel="alternate" href="{{ url_for("atom_feed") }}" type="application/atom+xml" title="{{ local_actor.display_name}}'s microblog">
+<link rel="icon" type="image/x-icon" href="/static/favicon.ico">
 <style>
 {{ highlight_css }}
 </style>

app/utils/favicon.py

@@ -0,0 +1,22 @@
+import sass  # type: ignore
+from PIL import Image
+from PIL import ImageColor
+from PIL import ImageDraw
+
+
+def _get_primary_color() -> str:
+    """Small hack to get the theme primary color."""
+    compiled = sass.compile(
+        string=(
+            "@import 'app/scss/main.scss';\n"
+            "#favicon-color { color: $primary-color; }"
+        )
+    )
+    return compiled[len(compiled) - 11 : -4]
+
+
+def build_favicon() -> None:
+    """Builds a basic favicon with the theme primary color."""
+    im = Image.new("RGB", (32, 32), ImageColor.getrgb(_get_primary_color()))
+    ImageDraw.Draw(im)
+    im.save("app/static/favicon.ico")