all-posts page, page titles, index page

src/plugins.ts

@@ -0,0 +1,38 @@
+import type { Root, Paragraph, PhrasingContent } from 'mdast';
+import type { VFile } from 'vfile';
+import { visit } from 'unist-util-visit';
+import { toString } from 'mdast-util-to-string';
+import { writeFileSync } from 'node:fs';
+
+
+export function remarkDescription() {
+    return (tree: Root, vfile: VFile) => {
+        if (vfile.basename == 'advent-of-languages-2024-04.mdx') {
+            writeFileSync('tree.json', JSON.stringify(tree, undefined, 4));
+        }
+
+        let description: string | null = null;
+
+        visit(tree, 'paragraph', (node: Paragraph) => {
+            if (description !== null) return;
+            description = summarize(node);
+        });
+
+        // Astro exposes this as `remarkPluginFrontmatter` from render()
+        const astro = (vfile.data.astro ??= { frontmatter: {} }) as { frontmatter: Record<string, unknown> };
+        astro.frontmatter.description = description;
+    };
+}
+
+
+/**
+ * Convert a paragraph node to a plain-text string, stripping any
+ * MDX JSX elements (e.g. <Sidenote>) so their content doesn't
+ * leak into the summary.
+ */
+function summarize(par: Paragraph): string {
+    const filtered = par.children.filter(
+        (child: PhrasingContent) => !(child.type as string).startsWith('mdxJsx')
+    );
+    return toString({ type: 'paragraph', children: filtered });
+}