Indieweb draft, creates per-tag RSS feeds.

src/pages/blog/tag/[...tag].rss.xml.ts

@@ -0,0 +1,37 @@
+import { type CollectionEntry, getCollection } from "astro:content";
+import type { AstroUserConfig } from "astro";
+import { SITE_TITLE, SITE_DESCRIPTION } from "../../../consts";
+import rss from "@astrojs/rss";
+import { getPublishedPosts } from "../../../lib/blog";
+
+function publishedOnly(
+  p: CollectionEntry<"blog">,
+): p is CollectionEntry<"blog"> & { data: { pubDate: Date } } {
+  return p.data.pubDate !== undefined;
+}
+
+export async function GET(context: AstroUserConfig) {
+  const { tag: selectedTag } = context.params;
+  const posts = await getPublishedPosts(selectedTag);
+
+  return rss({
+    title: `${SITE_TITLE} - ${selectedTag}`,
+    description: SITE_DESCRIPTION,
+    site: context.site as string,
+    items: posts.map((post) => ({
+      ...post.data,
+      link: `/blog/${post.id}/`,
+    })),
+  });
+}
+
+export async function getStaticPaths() {
+  const posts = await getCollection("blog", publishedOnly);
+
+  const tags = posts.flatMap((p) => p.data.tags);
+
+  return tags.map((tag) => ({
+    params: { tag: tag },
+    props: { tag: tag },
+  }));
+}