[misc] use highlight.js for syntax highlighting in blog post (#18480)

svalentin · web-flow · commit 21156fdcd9ee · 2025-01-16T16:00:23.000Z
Toe get highlighting to work, we just need to import the CSS and run the highlight.js that does the highlighting in JS client side. We can add the lines at the top of the blog post to do this. I've made it only support bash and python for now to help with detection. But if we have a reason to, we can remove that and let it try them all. In a previous PR I've added the necessary `<code>` tags. Since we're highlighting nicely now, I also removed the extra indendation. I've also noticed that we're pretty good at specifying the language in code blocks in the changelog. So we can take that language and use it in the code block as a class to tell highlight.js exactly what language that code block is in. If this is useful, we can remove the limitation of only python and bash support from the top configuration in the future. This is useful for smaller blocks of a few lines where maybe it doesn't detect the language properly. Used on mypy 1.14 blog post - https://mypy-lang.blogspot.com/2024/12/mypy-114-released.html
diff --git a/misc/gen_blog_post_html.py b/misc/gen_blog_post_html.py
@@ -44,16 +44,23 @@ def format_code(h: str) -> str:
     while i < len(a):
         if a[i].startswith("    ") or a[i].startswith("```"):
             indent = a[i].startswith("    ")
+            language: str = ""
             if not indent:
+                language = a[i][3:]
                 i += 1
-            r.append("<pre><code>")
+            if language:
+                r.append(f'<pre><code class="language-{language}">')
+            else:
+                r.append("<pre><code>")
             while i < len(a) and (
                 (indent and a[i].startswith("    ")) or (not indent and not a[i].startswith("```"))
             ):
                 # Undo &gt; and &lt;
                 line = a[i].replace("&gt;", ">").replace("&lt;", "<")
-                if not indent:
-                    line = "    " + line
+                if indent:
+                    # Undo this extra level of indentation so it looks nice with
+                    # syntax highlighting CSS.
+                    line = line[4:]
                 r.append(html.escape(line))
                 i += 1
             r.append("</code></pre>")
@@ -64,7 +71,7 @@ def format_code(h: str) -> str:
             i += 1
     formatted = "\n".join(r)
     # remove empty first line for code blocks
-    return re.sub(r"<code>\n", r"<code>", formatted)
+    return re.sub(r"<code([^\>]*)>\n", r"<code\1>", formatted)
 
 
 def convert(src: str) -> str:
@@ -131,8 +138,18 @@ def convert(src: str) -> str:
         h,
     )
 
-    # Add missing top-level HTML tags
-    h = '<html>\n<meta charset="utf-8" />\n<body>\n' + h + "</body>\n</html>"
+    # Add top-level HTML tags and headers for syntax highlighting css/js.
+    # We're configuring hljs to highlight python and bash code. We can remove
+    # this configure call to make it try all the languages it supports.
+    h = f"""<html>
+<meta charset="utf-8" />
+<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/styles/a11y-light.min.css">
+<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.9.0/highlight.min.js"></script>
+<script>hljs.configure({{languages:["python","bash"]}});hljs.highlightAll();</script>
+<body>
+{h}
+</body>
+</html>"""
 
     return h
 
