From 95349ee4276450bb46f7765ff5f7ff4a442eed38 Mon Sep 17 00:00:00 2001
From: soloturn <soloturn@gmail.com>
Date: Wed, 11 Nov 2026 20:32:27 +0100
Subject: [PATCH] fix: fail the build when two blog posts share a slug

Slugs come from the title, and a repeat silently overwrote the earlier post. generateId now throws naming both directories. Checked with a planted duplicate. Refs #213.

Co-Authored-By: soloturn <soloturn@gmail.com>
---
 src/content.config.ts | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/content.config.ts b/src/content.config.ts
index 9a52bea7..55ef4073 100644
--- a/src/content.config.ts
+++ b/src/content.config.ts
@@ -13,12 +13,27 @@ const issue = z.object({
   url: z.string(),
 });
 
+// Slugs handed out so far, by post directory. Two posts with one slug would
+// silently overwrite each other, so a repeat fails the build instead.
+const blogSlugs = new Map<string, string>();
+
 const blog = defineCollection({
   // Slug = kebab-cased title, as on the Gatsby site (/blog/<slug>).
   loader: glob({
     base: "./blog",
     pattern: "*/index.md",
-    generateId: ({ data }) => kebabCase(String(data.title)),
+    generateId: ({ entry, data }) => {
+      const slug = kebabCase(String(data.title));
+      for (const [other, taken] of blogSlugs) {
+        if (taken === slug && other !== entry) {
+          throw new Error(
+            `Blog posts ${other} and ${entry} both map to /blog/${slug}; retitle one.`,
+          );
+        }
+      }
+      blogSlugs.set(entry, slug);
+      return slug;
+    },
   }),
   schema: ({ image }) =>
     z.object({