[v6] disallow number in getStaticPaths params (#12608)

Co-authored-by: Florian Lefebvre <contact@florian-lefebvre.dev>
Co-authored-by: Armand Philippot <git@armand.philippot.eu>

Author: 3 people

src/content/docs/en/guides/upgrade-to/v6.mdx

@@ -840,6 +840,43 @@ If you want to keep the old ID generation for backward compatibility reasons, yo
 
 <ReadMore>Learn more about [Heading IDs](/en/guides/markdown-content/#heading-ids).</ReadMore>
 
+### Changed: `getStaticPaths()` cannot return `params` of type number
+
+<SourcePR number="14586" title="fix!: disallow number in getStaticPaths params"/>
+
+In Astro 5.x, `getStaticPaths()` could return `params` of type number, which would always be stringified by Astro. However, that could be confusing because it conflicted with `Astro.params` types.
+
+Astro 6.0 removes this behavior: `getStaticPaths()` must now return string or undefined `params` values.
+
+#### What should I do?
+
+Review your dynamic routes using `getStaticPaths()` and convert any number params to strings:
+
+```astro title="src/pages/post/[id]/[label].astro" del={6,13} ins={7,14}
+---
+export function getStaticPaths() {
+  return [
+    {
+      params: {
+        id: 1,
+        id: "1",
+        label: "foo",
+      }
+    },
+    {
+      params: {
+        id: 2,
+        id: "2",
+        label: "bar",
+      }
+    },
+  ]
+}
+---
+```
+
+<ReadMore>Learn more about [dynamic SSG routes with `getStaticPaths()`](/en/guides/routing/#static-ssg-mode).</ReadMore>
+
 ## Community Resources
 
 Know a good resource for Astro v5.0? [Edit this page](https://github.com/withastro/docs/edit/main/src/content/docs/en/guides/upgrade-to/v6.mdx) and add a link below!